RoboteQ AX2850 User Manual

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AX2550 AX2850

Dual Channel High Power Digital Motor Controller

User’s Manual

v1.9b, June 1, 2007

visit www.roboteq.com to download the latest revision of this manual

2 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Revision History

Date Version Changes

June 1, 2007 1.9b Added Output C active when Motors On

Fixed Encoder Limit Switches

Protection in case of Encoder failure in Closed Loop Speed

Added Short Circuit Protection (with supporting hardware)

Added Analog 3 and 4 Inputs (with supporting hardware)

Added Operating Mode Change on-the-fly

Changeable PWM frequency

Selectable polarity for Dead Man Switch

Modified Flashing Pattern

Separate PID Gains for Ch1 and C2, changeable on-the-fly

Miscellaneous additions and correction

Added Amps Calibration option

January 10, 2007 1.9 Changed Amps Limit Algorithm

Miscellaneous additions and correction

Console Mode in Roborun

March 7, 2005 1.7b Updated Encoder section.

February 1, 2005 1.7 Added Position mode support with Optical Encoder

Miscellaneous additions and corrections

April 17, 2004 1.6 Added Optical Encoder support

March 15, 2004 1.5 Added finer Amps limit settings

Enhanced Roborun utility

August 25, 2003 1.3 Added Closed Loop Speed mode

Added Data Logging support

Removed RC monitoring

August 15, 2003 1.2 Modified to cover AX2550 controller design

Changed Power Connection section

April 15, 2003 1.1 Added analog mode section

Added position mode section

Added RCRC monitoring feature

Updated Roborun utility section

Modified RS232 watchdog

March 15, 2003 1.0 Initial Release

The information contained in this manual is believed to be accurate and reliable. However, it may contain errors that were not noticed at time of publication. User’s are expected to perform their own product validation and not rely solely on data contained in this manual.

AX2550 Motor Controller User’s Manual 3

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Revision History 3

SECTION 1 Important Safety Warnings 13

This product is intended for use with rechargeable batteries 13 Do not Connect to a RC Radio with a Battery Attached 13 Beware of Motor Runaway in Improperly Closed Loop 13

SECTION 2 AX2550

Quick Start 15

What you will need 15 Locating the Switches, Wires and Connectors 15 Connecting to the Batteries and Motors 17 Connecting to the 15-pin Connector 18 Connecting the R/C Radio 19 Powering On the Controller 20 Button Operation 20 Default Controller Configuration 21 Connecting the controller to your PC using Roborun 22 Obtaining the Controller’s Software Revision Number 23 Exploring further 24

SECTION 3 AX2550 Motor Controller Overview 25

Product Description 25 Technical features 26

SECTION 4 Connecting Power and Motors to the Controller 29

Power Connections 29 Controller Power 30 Controller Powering Schemes 32

Powering the Controller from a single Battery 32

Powering the Controller Using a Main and Backup Battery 33 Connecting the Motors 34 Single Channel Operation 35

Converting the AX2550 to Single Channel 35 Power Fu ses 36 Wire Length Limits 37 Electrical Noise Reduction Techniques 37 Power Regeneration Considerations 37 Overvoltage Protection 38 Undervoltage Protection 38 Using the Controller with a Power Supply 39

AX2550 Motor Controller User’s Manual 5

SECTION 5 General Operation 41

Basic Operation 41 Input Command Modes 41 Selecting the Motor Control Modes 42

Open Loop, Separate Speed Control 42 Open Loop, Mixed Speed Control 42 Closed Loop Speed Control 43

Close Loop Position Control 43 User Selected Current Limit Settings 44 Temperature-Based Current Limitation 44 Battery Current vs. Motor Current 45 Regeneration Current Limiting 46 Programmable Acceleration 47 Command Control Curves 48 Left / Right Tuning Adjustment 49 Activating Brake Release or Separate Motor Excitation 51 Emergency Shut Down Using Controller Switches 51 Emergency Stop using External Switch 51 Inverted Operation 52 Special Use of Accessory Digital Inputs 52

Using the Inputs to Activate the Buffered Output 52

Using the Inputs to turn Off/On the Power MOSFET

transistors 52 Self-Test Mode 53

SECTION 6 Connecting Sensors and Actuators to Input/Outputs 55

AX2550 Connections 55 AX2550’s Inputs and Outputs 57 I/O List and Pin Assignment 58 Connecting devices to Output C 59 Connecting Switches or Devices to Input E 60 Connecting Switches or Devices to Input F 61 Connecting Switches or Devices to EStop/Invert Input 62 Analog Inputs 63 Connecting Position Potentiometers to Analog Inputs 63 Connecting Tachometer to Analog Inputs 64 Connecting External Thermistor to Analog Inputs 66 Using the Analog Inputs to Monitor External Voltages 67 Connecting User Devices to Analog Inputs 67 Internal Voltage Monitoring Sensors 68 Internal Heatsink Temperature Sensors 68 Temperature Conversion C Source Code 69

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SECTION 7 Installing, Connecting and Using the Encoder Module 71

Optical Incremental Encoders Overview 71 Recommended Encoder Types 72 Installing the Encoder Module 73 Connecting the Encoder 75 Cable Length and Noise Considerations 76 Motor - Encoder Polarity Matching 76 Voltage Levels, Thresholds and Limit Switches 76 Wiring Optional Limit Switches 78 Wiring Limit Switches Without Encoders 79 Effect of Limit Switches 79 Using the Encoder Module to Measure Distance 80 Using the Encoder to Measure Speed 80 Using the Encoder to Track Position 81 RS232 Communication with the Encoder Module 82 Encoder Testing and Setting Using the PC Utility 83

SECTION 8 Closed Loop Position Mode 85

Mode Description 85 Selecting the Position Mode 85 Position Sensor Selection 86 Sensor Mounting 86 Feedback Potentiometer wiring 87

Feedback Potentiometer wiring in RC or RS232 Mode 87 Feedback Potentiometer wiring in Analog Mode 88

Analog Feedback on Single Channel Controllers 89

Feedback Wiring in RC or RS232 Mode on Single Channel Controllers 89

Feedback Wiring in Analog Mode on Single Channel

Controllers 89 Using Optical Encoders in Position Mode 90 Sensor and Motor Polarity 90 Encoder Error Detection and Protection 91 Adding Safety Limit Switches 91 Using Current Limiting as Protection 93 Control Loop Description 93 PID tuning in Position Mode 94

SECTION 9 Closed Loop Speed Mode 97

Mode Description 97 Selecting the Speed Mode 97 Using Optical Encoder for Speed Feedback (AX2850 only) 98

AX2550 Motor Controller User’s Manual 7

Tachometer or Encoder Mounting 98 Tachometer wiring 98 Speed Sensor and Motor Polarity 99 Adjust Offset and Max Speed 100 Control Loop Description 100 PID tuning in Speed Mode 10 2

SECTION 10 Normal and

Fault Condition LED Messages 103

Use of the LED Display 103 Motor Direction Status 104 Fault Messages 105

No Control 105 Tem po ra r y F a u lt s 106 Permanent Faults 106

Self-Test Display 106

SECTION 11 R/C Operation 109

Mode Description 109 Selecting the R/C Input Mode 110 Connector I/O Pin Assignment (R/C Mode) 110 R/C Input Circuit Description 111 Supplied Cable Description 111 Powering the Radio from the controller 11 2 Connecting to a Separately Powered Radio 114 Operating the Controller in R/C mode 11 4 Reception Watchdog 115 R/C Transmitter/Receiver Quality Considerations 116 Joystick Deadband Programming 117 Command Control Curves 11 8 Left/Right Tuning Adjustment 118 Joystick Calibration 11 8 Automatic Joystick Calibration 119 Activating the Accessory Outputs 120 Data Logging in R/C Mode 121

SECTION 12 Analog Control and Operation 123

Mode Description 123 Connector I/O Pin Assignment (Analog Mode) 124 Connecting to a Voltage Source 125 Connecting a Potentiometer 125 Selecting the Potentiometer Value 126

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Analog Deadband Adjustment 127 Power-On S afet y 128 Under Voltage Safety 128 Data Logging in Analog Mode 128

SECTION 13 Serial (RS-232) Controls and Operation 131

Use and benefits of RS232 131 Connector I/O Pin Assignment (RS232 Mode) 132 Cable configuration 133 Extending the RS232 Cable 133 Communication Settings 134 Establishing Manual Communication with a PC 134

RS232 Communication with the Encoder Module 135

Entering RS232 from R/C or Analog mode 136

Data Logging String in R/C or Analog mode 136

RS232 Mode if default 137 Commands Acknowledge and Error Messages 137

Character Echo 137

Command Acknowledgement 137

Command Error 137

Watchdog time-out 137 RS-232 Watchdog 138 Controller Commands and Queries 138

Set Motor Command Value 139

Set Accessory Output 139

Query Power Applied to Motors 140

Query Amps from Battery to each Motor Channel 140

Query Analog Inputs 140

Query Heatsink Temperatures 141

Query Battery Voltages 141

Query Digital Inputs 142

Reset Controller 142 Accessing & Changing Configuration Parameter in Flash 143

Apply Parameter Changes 143

Flash Configuration Parameters List 144

Input Control Mode 145

Motor Control Mode 145

Amps Limit 146

Acceleration 147

Input Switches Function 147

RC Joystick or Analog Deadband 148

Exponentiation on Channel 1 and Channel 2 148

Left/Right Adjust 149

Default Encoder Time Base 1 and 2 149

Default Encoder Distance Divider 150

AX2550 Motor Controller User’s Manual 9

Default PID Gains 150 Joystick Min, Max and Center Values 150

Reading & Changing Operating Parameters at Runtime 151

Operating Modes Registers 152 Read/Change PID Values 152 PWM Frequency Register 153 Controller Status Register 153 Controller Identification Register 154 Current Amps Limit Registers 154

RS232 Encoder Command Set 155

Read Encoder Counter 155 Set/Reset Encoder Counters and Destination Registers 155 Read Speed 156 Read Distance 157 Read Speed/Distance 157 Read Encoder Limit Switch Status 157 Read / Modify Encoder Module Registers and Parameters 158

Encoder Hardware ID code 160 Switch Status 160 Speed or Distance 1 or 2 160 Counter Read/Write Mailbox 161 Counter 1 and 2 161 Destination Register 1 and 2 161 Distance 1 and 2 162 Speed 1 and 2 162 Time Base 1 and 2 162 Encoder Threshold 162

Distance Divider 162 Counter Read Data Format 163 Encoder Testing and Setting Using the PC Utility 163 Automatic Switching from RS232 to RC Mode 165 Analog and R/C Modes Data Logging String Format 166 Data Logging Cables 166 Decimal to Hexadecimal Conversion Table 167

SECTION 14 Configuring the Controller using the Switches 171

Programming Methods 171 Programming using built-in Switches and Display 171

Entering Programming Mode 172

Changing parameters 173

The Special Case of Joystick Calibration 173

Restoring factory defaults 173

Exiting the Parameter Setting Mode 174 Programmable Parameters List 174

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SECTION 15 Using the Roborun Configuration Utility 177

System Requirements 177 Downloading and Installing the Utility 177 Connecting the Controller to the PC 178 Roborun Frame, Tab and Menu Descriptions 179 Getting On-Screen Help 180 Loading, Changing Controller Parameters 181

Control Settings 181 Power Settings 182 Analog or R/C Specific Settings 183 Closed Loop Parameters 184

Encoder Setting and Testing 184

Encoder Module Parameters Setting 185 Exercising the Motors 186 Viewing Encoder Data 186

Running the Motors 186

Logging Data to Disk 189

Connecting a Joystick 190 Using the Console 191 Viewing and Logging Data in Analog and R/C Modes 192 Loading and Saving Profiles to Disk 192 Operating the AX2550 over a Wired or Wireless LAN 193 Updating the Controller’s Software 194

Updating the Encoder Software 195 Creating Customized Object Files 195

SECTION 16 Mechanical Specifications 197

Mechanical Dimensions 197 Mounting Considerations 198 Thermal Considerations 199 Attaching the Controller Directly to a Chassis 199 Wire Dimensions 199 Weight 200

AX2550 Motor Controller User’s Manual 11

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SECTION 1 Important Safety

Warnings

Read this Section First

The AX2550 is a high power electronics device. Serious damage, including fire, may occur to the unit, motors, wiring and batteries as a result of its misuse. Please review the User’s Manual for added precautions prior to applying full battery or full load power.

This product is intended for use with rechargeable batteries

Unless special precautions are taken, damage to the controller and/or power supply may occur if operated with a power supply alone. See“Power Regeneration Considerations” on page 37 of the Users Manual. Always keep the controller connected to the Battery. Use the Power Control input to turn On/Off.

Do not Connect to a RC Radio with a Battery Attached

Without proper protection, a battery attached to an RC Radio may inject its voltage directly inside the controller’s sensitive electronics. See

Beware of Motor Runaway in Improperly Closed Loop

Wiring or polarity errors between the feedback device and motor in position or closed loop position mode may cause the controller to runaway with no possibility to stop it until power is turned off.

AX2550 Motor Controller User’s Manual 13

Important Safety Warnings

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SECTION 2 AX2550

Quick Start

This section will give you the basic information needed to quickly install, setup and run your AX2550 controller in a minimal configuration. The AX2850 is a version of the AX2550 controller with the addition of Optical Encoder inputs.

What you will need

For a minimal installation, gather the following components:

• One AX2550 Controller and its provided cables

• 12V to 40V high capacity, high current battery

• One or two brushed DC motors

• One R/C to DB15 connector (provided)

• Miscellaneous wires, connectors, fuses and switch

Locating the Switches, Wires and Connectors

Take a moment to familiarize yourself with the controller’s wires, switches and con- nectors.

AX2550 Motor Controller User’s Manual 15

AX2550 Quick Start

The front side (shown in Figure 1) contains the buttons and display needed to operate and monitor the controller. The 15-pin connector provides the connection to the R/C radio, joystick or microcomputer, as well as connections to optional switches and sensors.

Program Set

Controller Configuration buttons

Connector to Optical Encoders (AX2850 only)

FIGURE 1. Front Controller Layout

At the back of the controller (shown in the figure below) are located all the wires that must be connected to the batteries and the motors.

Controller Power

Power Control

Yellow

Reset

Operating Status and Program LED Display

Ground (-)

Black

Connector to Receiver/Controls and sensors

(top)

Motor (+)

White

Motor (-)

Green

Motor 1

12 to 40V (+)

Red

Ground (-)

Black

12 to 40V (+)

Red

Motor 2

Motor(+) Yellow or

White

Motor (-)

Green

FIGURE 2. Rear Controller Layout

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Connecting to the Batteries and Motors

Connection to the batteries and motors is shown in the figure below and is done by connecting the set of wires coming out from the back of the controller.

Motor2

Motor1

Power switch

VMot

M1-

M1+

PwrCtrl

Controller

GND

M2-

M2+

VMot

Optional

Diode

Off

Optional Emergency Disconnect

12V to 24V Motor Battery

Fuse

Notes:

- The Battery Power connection are doubled in order to provide the maximum current to the controller. If only one motor is used, only one set of motor power cables needs to be connected.

- Typically, 1, 2 or 3 x 12V batteries are connected in series to reach 12, 24 or 36V respectively.

- The Power Control wire MUST be used to turn On and Off the controller.

FIGURE 3. AX2550 Electrical Power Wiring Diagram

1- Connect each motor to one of the two M+ and M- cables pairs. Make sure to respect the polarity, otherwise the motor(s) may spin in the opposite direction than expected

2- Connect the two thick black wires to the minus (-) terminal of the battery that will be used to power the motors. Connect the two thick red wires the two VMot terminals to the plus (+) terminal of the battery. The motor battery may be of 12 to 40 Volts. There is no need to insert a separate switch on Power cables, although one is suggested for Emergency disconnect. See “Controller Power” on page 30 for a detailed discussion and more wiring options.

Avoid extending the length of wires from the battery to the controller as the added inductance may cause damage to the controller when operating at high currents. Try extending the motor wires instead since the added inductance on the motor side of the controller is not harmful.

The two red wires are connected to each other inside the controller. The same is true for the black wires. You should wire each pair together as shown in the diagram above.

3- The yellow Power Control wire and the thin black wire MUST be connected to Ground to turn the Controller Off. For turning the controller On, even though the Power Control may be left floating, whenever possible pull it to an unfused12V or higher voltage to keep the controller logic solidly On. You may use a separate battery to keep the controller alive as the main Motor battery discharges. Refer to the chapter “Connecting Power and Motors to

AX2550 Motor Controller User’s Manual 17

AX2550 Quick Start

the Controller” on page 29 for more information about batteries and other connection options.

Important Warning

Do not rely on cutting power to the controller for it to turn off if the Power Control is left floating. If motors are spinning because the robot is pushed are pushed or because of inertia, they will act as generators and will turn the controller, possibly in an unsafe state. ALWAYS ground the Power Control wire to turn the controller Off and keep it Off.

Important Warning

The controller includes large capacitors. When connecting the Motor Power Cables, a spark will be generated at the connection point. This is a normal occurrence and should be expected.

Connecting to the 15-pin Connector

The controller’s I/O are located on it’s standard 15-pin D-Sub Connector. The functions of some pins varies depending on controller model and operating mode. Pin assignment is

found in the table below.

Signal

1 2A Digital Output C (same as pin 9)

2TxData

3 RC Ch1 RxData Unused

4 RC Ch 2 Digital Input F

5 Ground Out

6 Ground In

7 +5V In

8 Digital Input E (Not available when Encoder module is present)

9 2A Digital Output C (same as pin 1)

10 Analog Input 2

11 Analog Input 1

12 Analog Input 3 (on RevB hardware)

13 Ground Out

14 +5V Out (100mA max.)

15 Emergency Stop or Invert Switch input

RC Mode RS232 Mode Analog Mode

(Unused on RevB Hardware)

and Analog Input 4 (on RevB hardware only)

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Connecting the R/C Radio

Connect the R/C adapter cables to the controller on one side and to two or three channels on the R/C receiver on the other side. If present, the third channel is for activating the accessory outputs and is optional.

When operating the controller in “Separate” mode, the wire labelled Ch1 controls Motor1, and the wire labelled Ch2 controls Motor2.

When operating the controller in “Mixed” mode, Ch1 is used to set the robot’s speed and direction, while Ch2 is used for steering.

See “R/C Operation” on page 109 of the User’s Manual for a more complete discussion on R/C commands, calibration and other options.

Channel 3

Channel 2

Channel 1

Pin 1

FIGURE 4. R/C connector wiring for 3 channels and battery elimination (BEC)

This wiring - with the wire loop uncut - assumes that the R/C radio will be powered by the AX2550 controller. Other wiring options are described in “R/C Operation” on page 109 of the User’s Manual.

Important Warning

Do not connect a battery to the radio when the wire loop is uncut. The RC battery voltage will flow directly into the controller and cause permanent damage if its voltage is higher than 5.5V.

3: Channel 1 Command Pulses 4: Channel 2 Command Pulses 6: Radio battery (-) Ground 7: Radio battery (+) 8: Channel 3 Command Pulses

Wire loop bringing power from controller to RC radio

Connecting the optional channel 3 will enable you to turn on and off the accessory output. See “Connecting Sensors and Actuators to Input/Outputs” on page 55 and “Activating the Accessory Outputs” on page 120 of the User’s Manual.

AX2550 Motor Controller User’s Manual 19

AX2550 Quick Start

Powering On the Controller

Important reminder: There is no On-Off switch on the controller. You must insert a switch on the controller’s power wire as described in section“Connecting to the Batteries and Motors” on page 17.

To power the controller, center the joystick and trims on the R/C transmitter. In Analog mode, center the command potentiomenter or joystick.Then turn on the switch that you have placed on the on the Power Control input.

If the R/C transmitter and/or receiver is powered off, the display on the controller will alternate the letters spelling “no ctrl” to indicate that it is On but is not receiving a control signal.

FIGURE 5. “no control” scroll message indicates no valid R/C signal is present

Turn the R/C transmitter On. The “no ctrl” scrolling message will disappear and the display will show steady patterns depending on the motor’s selected direction.

Move the joystick on the transmitter to activate the motors to the desired speed and direction.

See “R/C Operation” on page 109 of the User’s Manual for a detailed description of the many features and options available in the R/C mode.

Button Operation

The AX2550 has three buttons: Set, Program and Reset. These buttons are not needed for normal operation, as the controller is immediately operational upon power up.

The Reset button will restart the controller. This button is recessed and you will need a paper clip to press it. Reset is also accomplished by turning the controller’s power Off and back On.

The Set and Program buttons have the following functions depending how and when they are pressed:

TABLE 1. AX2550 Buttons Function

Prog and Set button status Function

Press and hold Program alone during reset or power up Enter the Programming Mode.

Press and hold Set alone during reset of power up Enter Self-Test mode. See “Self-Test

Mode” on page 53 of the User’s Manual

Press and hold Program and Set together during reset or power up

Reset configuration parameters to factory default

20 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Default Controller Configuration

TABLE 1. AX2550 Buttons Function

Prog and Set button status Function

Press Program while Programming Mode Accept previous parameter change and

select next parameter

Press Set while in Programming mode Change value of selected parameter

Press Program pressed alone during normal operation No effect

Press Set alone during normal operation No effect

Press Program and Set together during normal operation Emergency stop

Default Controller Configuration

Version 1.9b of the AX2550 software is configured with the factory defaults shown in the table below. Although Roboteq strives to keep the same parameters and values from one version to the next, changes may occur from one revision to the next. Make sure that you have the matching manual and software versions. These may be retrieved from the Roboteq web site. See “Configuring the Controller using the Switches” on page 171 of the

User Manual for a complete configuration parameter list and their possible values.

TABLE 2. AX2550 Default Settings

Parameter Default Values Letter

Input Command mode: (0) = R/C Radio mode I

Motor Control mode (0) = Separate A, B, speed control, open loop C

Amp limit (5) = 105A A

Acceleration (2) = medium-slow S

Input switch function (3) = no action U

Joystick Deadband (2) = 16% d

Exponentiation on channel 1 (0) = Linear (no exponentiation) E

Exponentiation on channel 2 (0) = Linear (no exponentiation) F

Left / Right Adjust (7) = no adjustment L

Any one of the parameters listed in Table 2, and others not listed, can easily be changed either using the controller’s buttons or the PC with the Roboteq Configuration Utility. See “Using the Roborun Configuration Utility” on page 177.

The example below shows how to use the buttons to select and change the Motor Control mode from “separate” to “mixed”. See “Configuring the Controller using the Switches” on page 171 of the User’s Manual for a complete list of all the AX2550’s parameters and their meanings.

AX2550 Motor Controller User’s Manual 21

AX2550 Quick Start

Press & hold Prog

Program mode entered

Press Prog to select

Press Set to select

next value for parameter

Press Prog to store change

and select next parameter

Restart

after 10 seconds

next parameter

Reset controller

to exit

Press and hold the Prog button for 10 seconds while resetting or powering on the controller

After 10 seconds, the controller will enter the programming mode and flash alternatively the current parameter (I= Input Mode) and its value (0= R/C mode).

Press the Prog button to move to the next parameter (C= Motor Control Mode) and its value (0= Separate)

Press the Set button to change the parameter’s value (1= Combined)

Press the Prog button record the change and move to the next parameter (A= Amps limit) and it’s value (2= 75A)

Press the Reset button or power off/on the control to restart the controller using the new parameters.

Connecting the controller to your PC using Roborun

Connecting the controller to your PC is not necessary for basic R/C operation. However, it is a very simple procedure that is useful for the following purposes:

• to Read and Set the programmable parameters with a user-friendly graphical inter-

face

• to obtain the controller’s software revision and date

• to send precise commands to the motors

• to read and plot real-time current consumption value

• Save captured parameters onto disk for later analysis

• to update the controller’s software

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Obtaining the Controller’s Software Revision Number

FIGURE 6. Roborun Utility screen layout

To connect the controller to your PC, use the provided cable. Connect the 15-pin connector to the controller. Connect the 9-pin connector to your PC’s available port (typically COM1) - use a USB to serial adapter if needed. Apply power to the controller to turn it on.

Load your CD or download the latest revision of Roborun software from www.Roboteq.com, install it on your PC and launch the program. The software will automatically establish communication with the controller, retrieve the software revision number and present a series of buttons and tabs to enable its various possibilities.

The intuitive Graphical User Interface will let you view and change any of the controller’s parameters. The “Run” tab will present a number of buttons, dials and charts that are used for operating and monitoring the motors.

Obtaining the Controller’s Software Revision Number

One of the unique features of the AX2550 is the ability to easily update the controller’s operating software with new revisions downloaded from Roboteq’s web site at www.roboteq.com. This is useful for adding features and/or improving existing ones.

Each software version is identified with a unique number. Obtaining this number can be done using the PC connection discussed previously.

AX2550 Motor Controller User’s Manual 23

AX2550 Quick Start

FIGURE 7. Press and hold “Set” to display version number and enter self-test

It is also possible to get the controller to display the software version number by following these simple steps

• Disconnect the power from the motor batteries. Power the controller only via the

Power Control input.

• Press and hold the Set button while powering or resetting the controller.

The LED will display a sequence of two numerical digits and an optional letter separated by dashes as shown in the examples below.

= Software version 1.9b

After these digits are displayed, the controller will attempt to power the motors as part of the self test mode (see “Self-Test Mode” on page 53 of the User’s Manual for a more detailed explanation). This is why the motor’s battery must be disconnected. After about 30 seconds, the software revision number will be displayed again the cycle will repeat.

You will need to reset, or power down and up, the controller to exit and resume normal operation.

Now that you know your controller’s software version number, you will be able to see if a new version is available for download and installation from Roboteq’s web site and which features have been added or improved.

Installing new software is a simple and secure procedure, fully described in “Updating the Controller’s Software” on page 194 of the User’s Manual.

Exploring further

By following this quick-start section, you should have managed to get your controller to operate in its basic modes within minutes of unpacking.

Each of the features mentioned thus far has numerous options which are discussed further in the complete User’s Manual, including:

• Self test mode

• Emergency stop condition

• Joystick calibration

• Using Inputs/Outputs

• Current limiting

• Closed Loop Operation

• Software updating

• and much more

24 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

SECTION 3 AX2550 Motor

Controller Overview

Congratulations! By selecting Roboteq’s AX2550 you have empowered yourself with the industry’s most versatile, powerful and programmable DC Motor Controller for mobile robots. This manual will guide you step by step through its many possibilities.

Product Description

The AX2550 is a highly configurable, microcomputer-based, dual-channel digital speed or position controller with built-in high power drivers. The controller is designed to interface directly to high power DC motors in computer controlled or remote controlled mobile robotics and automated vehicle applications.

The AX2550 controller can accept speed or position commands in a variety of ways: pulse-width based control from a standard Radio Control receiver, Analog Voltage commands, or RS-232 commands from a microcontroller or wireless modem.

The controller's two channels can be operated independently or can be combined to set the forward/reverse direction and steering of a vehicle by coordinating the motion on each side of the vehicle. In the speed control mode, the AX2550 can operate in open loop or closed loop. In closed loop operation, actual speed measurements from tachometers or optical encoders are used to verify that the motor is rotating at the desired speed and direction and to adjust the power to the motors accordingly.

The AX2550 can also be configured to operate as a precision, high torque servo controller. When connected to a potentiometer coupled to the motor assembly, the controller will command the motor to rotate up to a desired angular position. Depending on the DC motor's power and gear ratio, the AX2550 can be used to move or rotate steering columns or other physical objects with very high torque.

The AX2550 is fitted with many safety features ensuring a secure power-on start, automatic stop in case of command loss, over current protection on both channels, and overheat protection.

AX2550 Motor Controller User’s Manual 25

AX2550 Motor Controller Overview

The motors are driven using high-efficiency Power MOSFET transistors controlled using Pulse Width Modulation (PWM) at 16kHz. The AX2550 power stages can operate from 12 to 40VDC and can sustain up to 120A of controlled current, delivering up to 4,800W (approximately 6 HP) of useful power to each motor.

The many programmable options of the AX2550 are easily configured using the supplied PC utility or one-touch Program and Set buttons and a 7-segment LED display. Once programmed, the configuration data are stored in the controller's non-volatile memory, eliminating the need for cumbersome and unreliable jumpers.

The AX2850 is the AX2550 controller fitted with a dual channel optical encoder input module. Optical Encoders allow precise motor speed and position measurement and enable advance robotic applications.

Technical features

Fully Digital, Microcontroller-based Design

• Multiple operating modes

• Fully programmable using either built-in switches and 7 segment display or through

connection to a PC

• Non-volatile storage of user configurable settings

• Simple operation

• Software upgradable with new features

Multiple Command Modes

• Radio-Control Pulse-Width input

• Serial port (RS-232) input

• 0-5V Analog Command input

Multiple Advanced Motor Control Modes

• Independent operation on each channel

• Mixed control (sum and difference) for tank-like steering

• Open Loop or Closed Loop Speed mode

• Position control mode for building high power position servos

• Modes selectable independently for each channel

Automatic Joystick Command Corrections

• Joystick min, max and center calibration

• Selectable deadband width

• Selectable exponentiation factors for each joystick

• 3rd R/C channel input for accessory output activation (disabled when encoder mod-

ule present)

Special Function Inputs/Outputs

• 2 Analog inputs. Used as:

26 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Technical features

• Tachometer inputs for closed loop speed control

• Potentiometer input for position (servo mode)

• Motor temperature sensor inputs

• External voltage sensors

• User defined purpose (RS232 mode only)

• 2 Extra analog inputs (on RevB hardware). Used as:

• Potentiometer input for position while in analog command mode

• User defined purpose (RS232 mode only)

• One Switch input configurable as

• Emergency stop command

• Reversing commands when running vehicle inverted

• General purpose digital input

• One general purpose 24V, 2A output for accessories

• Up to 2 general purpose digital inputs

Optical Encoder Inputs (AX2850 only)

• Inputs for two Quadrature Optical Encoders

• up to 250khz Encoder frequency per channel

• two 32-bit up-down counters

• Inputs may be shared with four optional limit switches per channel

Internal Sensors

• Voltage sensor for monitoring the main 12 to 40V battery system operation

• Voltage monitoring of internal 12V

• Temperature sensors on the heat sink of each power output stage

• Sensor information readable via RS232 port

Low Power Consumption

• On board DC/DC converter for single 12 to 40V battery system operation

• Optional backup power input for powering safely the controller if the motor batteries

are discharged

• Max 200mA at 12V or 100mA at 24V idle current consumption

• Power Control wire for turning On or Off the controller from external microcomputer

or switch

• No power consumed by output stage when motors are stopped

• Regulated 5V output for powering R/C radio. Eliminates the need for separate R/C

battery

High Efficiency Motor Power Outputs

• Two independent power output stages

• Optional Single Channel operation at double the current

• Dual H bridge for full forward/reverse operation

• Ultra-efficient 2.5mOhm (1.25mOhm on HE version) ON resistance (RDSon) MOS-

FET transistors

• Synchronous Rectification H Bridge

AX2550 Motor Controller User’s Manual 27

AX2550 Motor Controller Overview

• 12 to 40 V operation

• High current 8 AWG cable sets for each power stages

• Temperature-based Automatic Current Limitation

• 120A up to 15 seconds (per channel)

• 100A up to 30 seconds

• 80A extended

• High current operation may be extended with forced cooling

• 250A peak Amps per channel

• 16kHz Pulse Width Modulation (PWM) output

• Auxiliary output for brake, clutch or armature excitation

• Heat sink extruded case

Advanced Safety Features

• Safe power on mode

• Optical isolation on R/C control inputs

• Automatic Power stage off in case of electrically or software induced program fail-

ure

• Overvoltage and Undervoltage protection

• Regeneration current limiting

• Watchdog for automatic motor shutdown in case of command loss (R/C and RS232

modes)

• Large, bright run/failure diagnostics on 7 segment LED display

• Programmable motor acceleration

• Built-in controller overheat sensor

• Emergency Stop input signal and button

Data Logging Capabilities

• 13 internal parameters, including battery voltage, captured R/C command, tempera-

ture and Amps accessible via RS232 port

• Data may be logged in a PC, PDA or microcomputer

Sturdy and Compact Mechanical Design

• Built from aluminum heat sink extrusion with mounting brackets

• Efficient heat sinking. Operates without a fan in most applications.

• 7” (178mm) long (excluding mounting brackets) by 5.5” wide (140mm) by 1.8”

(40mm) high

• -20o to +85o C case operating environment

• 3.3 lbs (1500g)

28 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Power Connections

SECTION 4 Connecting

Power and Motors to the Controller

This section describes the AX2550 Controller’s connections to power sources and motors.

Important Warning

Please follow the instructions in this section very carefully. Any problem due to wiring errors may have very serious consequences and will not be covered by the product’s warranty.

Power Connections

The AX2550 has three Ground (black), two Vmot (red) power cables and a Power Control wire (yellow). The power cables are located at the back end of the controller. The various power cables are identified by their position, wire thickness and color: Red is positive (+), black is negative or ground (-).

The power connections to the batteries and motors are shown in the figure below.

AX2550 Motor Controller User’s Manual 29

Connecting Power and Motors to the Controller

Controller Power

Power Control

Ye l l o w

Motor (+)

White

Motor (-)

Green

12 to 40V (+)

Red

Motor 1

FIGURE 8. Controller rear plate and power wiring

Ground (-)

Black

Ground (-)

Black

12 to 40V (+)

Red

Motor(+) Ye l l o w o r

Motor 2

(top)

Motor (-)

Green

White

Controller Power

The AX2550 uses a flexible power supply scheme that is best described in Figure 9. In this diagram, it can be seen that the power for the Controller’s microcomputer is separate from this of the motor drivers. The microcomputer circuit is connected to a DC/DC converter which takes power from either the Power Control wire or the VMot input. The diode circuit is designed to automatically select one power source over the other, letting through the source that is higher than the other.

30 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Controller Power

Mot1(-)

Mot1(+)

Channel 1 MOSFET Power Stage

Microcomputer &

MOSFET Drivers

Channel 2 MOSFET Power Stage

9.5V min 13V max

DC/DC

ENABLE

10.5V min 40V max

FIGURE 9. Representation of the AX2550’s Internal Power Circuits

When powered only via the Power Control input, the controller will turn On but motors will not be able to turn until power is also present on the VMot wires

The Power Control input also ser ves as the Enable signal for the DC/DC converter. When floating or pulled to above 1V, the DC/DC converter is active and supplies the AX2550’s microcomputer and drivers, thus turning it On. When the Power Control input is pulled to Ground, the DC/DC converter is stopped and the controller is turned Off.

5Vmin

40V max

5Vmin

40V max

VBatt Vmot

GND

Power Control &Backup

GND

VBatt Vmot

Mot2(+)

Mot2(-)

The yellow Power Control wire and the thin black wire MUST be connected to Ground to turn the Controller Off. For turning the controller On, even though the Power Control may be left floating, whenever possible pull it to an unfused12V or higher voltage to keep the controller logic solidly On. You may use a separate battery to keep the controller alive as the main Motor battery discharges.

The table below shows the state of the controller depending on the voltage applied to Power Control and Vmot.

TABLE 3. Controller Status depending on Power Control and VMot

Power Control input is connected to

And Main Battery Voltage is Action

Ground Any Voltage from 0V to 40V Controller is Off

Floating 0V Controller is Off. Not Recom-

mended Off Configuration.

Floating Between 8V and 10.5V Controller Logic is On

Power Stage is Disabled (undervoltage condition)

Floating Between 10.5 and 40V Controller is On.

Power Stage is Active

AX2550 Motor Controller User’s Manual 31

Connecting Power and Motors to the Controller

TABLE 3. Controller Status depending on Power Control and VMot

Power Control input is connected to

And Main Battery Voltage is Action

10.5V to 40V 0V Controller is On.

Power Stage is Off

10.5V to 40V 1V to 40V Controller is On.

Power Stage is Active

All 3 ground (-) are connected to each other inside the controller. The two main battery wires are also connected to each other internally. However, you must never assume that connecting one wire of a given battery potential will eliminate the need to connect the other.

Controller Powering Schemes

Powering the Controller from a single Battery

The diagram on Figure 12 show how to wire the controller to a single battery circuit and how to turn power On and Off.

Motor2

Power on/off

switch

Fuse

Optional

Emergency Disconnect

12V to 24V

Motor Battery

Motor1

VMot

M1+

M1-

GND

VCon

Controller

GND

M2-

M2+

VMot

Notes:

- The Battery Power connection are doubled in order to provide the maximum current to the controller. If only one motor is used, only one set of motor power cables needs to be connected.

- Typically, 1, 2 or 3 x 12V batteries are connected in series to reach 12V, 24V or 36V respectively.

FIGURE 10. Powering the AX2550 from a single battery

Connect the two thick black wires to the minus (-) terminal of the battery that will be used to power the motors. Connect the two thick red wires to the plus (+) terminal of the battery. The motor battery may be of 12 to 40 Volts.

32 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

There is no need to insert a separate switch on Power cables, although for safety reasons, it is highly recommended that a way of quickly disconnecting the Motor Power be provided in the case of loss of control and all of the AX2550 safety features fail to activate.

The two red wires are connected to each other inside the controller. The same is true for the black wires. You should wire each pair together as shown in the diagram above.

The yellow Power Control wire and the thin black wire MUST be connected to Ground to turn the Controller Off. When the controller is Off, the output transistors are in the Off position and no power is drawn on VMot.

For turning the controller On, even though the Power Control may be left floating, whenever possible pull it to an unfused12V or higher voltage to keep the controller logic solidly On. In applications where the motors could be made to run through external force (electric vehicle going downhill, for example), and generate 40V or more, a diode should be placed across the fuse & emergency switch to provide a path, under all circumstances, for the regeneration current. See “Power Regeneration Considerations” on page 37.

Important Warning

Controller Powering Schemes

Do not rely on cutting power to the controller for it to turn off if the Power Control is left floating. If motors are spinning because the robot is pushed are pushed or because of inertia, they will act as generators and will turn the controller On, possibly in an unsafe state. ALWAYS ground the Power Control wire to turn the controller Off and keep it Off.

Important Warning

On versions of the AX2550 with PCB revision number lower than 5.2, the backup power supply applied on the Power Control wire must NEVER EXCEED 13V. Permanent damage may otherwise occur. The PCB revision number can be found on the sticker on the case’s bottom.

Important Warning

Always connect the thick black wires to ground BEFORE connecting the red wires to the battery. If the motors are activated while the connection to ground is done solely via the thin black wire (or the ground wire in the RS232 cable), the ground wire will

overheat and/or melt .

Powering the Controller Using a Main and Backup Battery

In typical applications, the main motor batteries will get eventually weaker and the voltage will drop below the level needed for the internal microcomputer to properly operate. For all professional applications it is therefore recommended to add a separate 12V (to 40V) power supply to ensure proper powering of the controller under any conditions. This dual battery configuration is highly recommended in 12V systems.

AX2550 Motor Controller User’s Manual 33

Connecting Power and Motors to the Controller

Motor2

Motor1

M1-

M1+

VMot

PwrCtrl

Controller

Power switch

GND

FIGURE 11. Powering the AX2550 with a Main and Backup Supply

Important Warning

Unless you can ensure a steady 12V to 40V voltage in all conditions, it is recommended that the battery used to power the controller’s electronics be separate from the one used to power the motors. This is because it is very likely that the motor batteries will be subject to very large current loads which may cause the voltage to eventually dip below 12V as the batteries’ charge drops. The separate backup power supply should be connected to the Power Control input.

M2-

M2+

VMot

Off

12V to 40V

Motor Battery

12V to 40V

Backup Battery

Connecting the Motors

Connecting the motors is simply done by connecting each motor terminal to the M1+ (M2+) and M1- (M2-) wires. Which motor terminal goes to which of the + or - controller output is typically determined empirically.

After connecting the motors, apply a minimal amount of power using the Roborun PC utility with the controller configured in Open Loop speed mode. Verify that the motor spins in the desired direction. Immediately stop and swap the motor wires if not.

In Closed Loop Speed or Position mode, beware that the motor polarity must match this of the feedback. If it does not, the motors will runaway with no possibility to stop other than switching Off the power. The polarity of the Motor or off the feedback device may need to be changed.

Important Warning

Make sure that your motors have their wires isolated from the motor casing. Some motors, particularly automotive parts, use only one wire, with the other connected to the motor’s frame.

34 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Single Channel Operation

If you are using this type of motor, make sure that it is mounted on isolators and that its casing will not cause a short circuit with other motors and circuits which may also be inadvertently connected to the same metal chassis.

Single Channel Operation

The AX2550’s two channel outputs can be paralleled as shown in the figure below so that they can drive a single load with twice the power. To perform in this manner, the controller’s Power Transistor that are switching in each channel must be perfectly synchronized. Without this synchronization, the current will flow from one channel to the other and cause the destruction of the controller.

The controller may be ordered with the -SC (Single Channel) suffix. This version incorporates a hardware setting inside the controller which ensures that both channels switch in a synchronized manner and respond to commands sent to channel 1.

Warning:

Use this wiring only with

-SC versions (Single Channel) of the controller

VMot

FIGURE 12. Wiring for Single Channel Operation

Converting the AX2550 to Single Channel

The AX2550 can be easily modified into a Single Channel version by placing a jumper on the PCB. This step must be undertook only if you have the proper tooling and technical skills.

• Disconnect the controller from power

• Open the controller’s case by removing the front bracket and sliding the cover off

• Depending on the board’s revision, place a drop of solder on the PCB jumper pad

shown in Figure 13 or insert a jumper as shown in Figure 14.

• Place the cover and bracket back

M1-

M1+

VCon

Controller

GND

M2-

M2+

Pwr Ctrl

12V to 40V

GND

VMot

Before paralleling the outputs,

• Place the load on channel 1 and verify that it is activated by commands on channel

AX2550 Motor Controller User’s Manual 35

Connecting Power and Motors to the Controller

• Then place the load on channel 2 and verify that is also activated by commands on

channel 1.

• Commands on channel 2 should have no effects on either output.

It will be safe to wire in parallel the controller’s outputs only after you have verified that both outputs react identically to channel 1 commands.

MCU

Single Channel

FIGURE 13. Solder Jumper setting for Single Channel Operation

Jumper "open"

Xilinx

Place solder ball to close jumper and enable single channel mode

MCU

Jumper In for

Single Channel

FIGURE 14. Jumper setting for Single Channel Operation - RevB Hardware

Xilinx

Power Fuses

For low Amperage applications (below 30A per motor), it is recommended that a fuse be inserted in series with the main battery circuit as shown in the Figure 10 on page 32.

The fuse will be shared by the two output stages and therefore must be placed before the Y connection to the two power wires. Fuse rating should be the sum of the expected current on both channels. Note that automotive fuses are generally slow will be of limited effectiveness in protecting the controller and may be omitted in high current application. The fuse will mostly protect the wiring and battery against after the controller has failed.

Important Warning

Fuses are typically slow to blow and will thus allow temporary excess current to flow through them for a time (the higher the excess current, the faster the fuse will blow). This characteristic is desirable in most cases, as it will allow motors to draw surges

36 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

during acceleration and braking. However, it also means that the fuse may not be able to protect the controller.

Wire Length Limits

The AX2550 regulates the output power by switching the power to the motors On and Off at high frequencies. At such frequencies, the wires’ inductance produces undesirable effects such as parasitic RF emissions, ringing and overvoltage peaks. The controller has built-in capacitors and voltage limiters that will reduce these effects. However, should the wire inductance be increased, for example by extending the wire length, these effects will be amplified beyond the controller’s capability to correct them. This is particularly the case for the main battery power wires (thick red and black cables).

Important Warning

Avoid extending the black and red Motor Power wires beyond their original length, as the added inductance may cause damage to the controller when operating at high currents. Try extending the motor wires instead since the added inductance is less harmful on this side of the controller.

Wire Length Limits

If the controller must be located at a longer distance, the effects of the wire inductance may be reduced by using one or more of the following techniques:

• Twisting the power and ground wires over the full length of the wires

• Use the vehicle’s metallic chassis for ground and run the positive wire along the sur-

face

• Add a capacitor (5,000uF or higher) near the controller

Electrical Noise Reduction Techniques

As discussed in the above section, the AX2550 uses fast switching technology to control the amount of power applied to the motors. While the controller incorporates several circuits to keep electrical noise to a minimum, additional techniques can be used to keep the noise low when installing the AX2550 in an application. Below is a list of techniques you can try to keep noise emission low:

• Keep wires as short as possible

• Loop wires through ferrite cores

• Add snubber R/C circuit at motor terminals

• Keep controller, wires and battery enclosed in metallic body

Power Regeneration Considerations

When a motor is spinning faster than it would normally at the applied voltage, such as when moving downhill or decelerating, the motor acts like a generator. In such cases, the current will flow in the opposite direction, back to the power source.

AX2550 Motor Controller User’s Manual 37

Connecting Power and Motors to the Controller

It is therefore essential that the AX2550 be connected to rechargeable batteries. If a power supply is used instead, the current will attempt to flow back in the power supply during regeneration, potentially damaging it and/or the controller.

Regeneration can also cause potential problems if the battery is disconnected while the motors are still spinning. In such a case, and depending on the command level applied at that time, the regenerated current will attempt to flow back to the battery. Since none is present, the voltage will rise to potentially unsafe levels. The AX2550 includes an overvoltage protection circuit to prevent damage to the output transistors (see “Overvoltage Protection” on page 38). However, if there is a possiblity that the motor could be made to spin and generate a voltage higher than 40V, a path to the battery must be provided, even after a fuse is blown. This can be accomplished by inserting a diode across the fuse as shown in Figure 10 on page 32.

Please download the Application Note “Understanding Regeneration” from the www.roboteq.com for an in-depth discussion of this complex but important topic.

Important Warning

Use the AX2550 only with a rechargeable battery as supply to the Motor Power wires (thick black and red wires). If a transformer or power supply is used, damage to the controller and/or power supply may occur during regeneration. See “Using the Controller with a Power Supply” on page 39 for details.

Important Warning

Avoid switching Off or cutting open the main power cables (thick black and red wires) while the motors are spinning. Damage to the controller may occur.

Overvoltage Protection

The AX2550 includes a battery voltage monitoring circuit that will cause the output transistors to be turned Off if the main battery voltage applied on the thick red and black wires rises above 43V.

This protection is designed to prevent the voltage created by the motors during regeneration to be “amplified” to unsafe levels by the switching circuit.

The controller will resume normal operation when the measured voltage drops below 43V.

Undervoltage Protection

In order to ensure that the power MOSFET transistors are switched properly, the AX2550 monitors the internal 12V power supply that is used by the MOSFET drivers. If the internal voltage drops below 10V, the controller’s output stage is turned Off. The rest of the control- ler’s electronics, including the microcomputer, will remain operational as long as the internal voltage is above 8V.

The internal voltage will be the output of the DC/DC converter which will be a solid 12V as long as either of the main battery or backup voltage is higher than 12.5V. If the main and

38 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Using the Controller with a Power Supply

backup voltage drop below 12.V, the DC/DC converter’s output will be approximately 0.5V lower than the highest input.

Using the Controller with a Power Supply

Using a transformer or a switching power supply is possible but requires special care, as the current will want to flow back from the motors to the power supply during regeneration. As discussed in “Power Regeneration Considerations” on page 37, if the supply is not able to absorb and dissipate regenerated current, the voltage will increase until the overvoltage protection circuit cuts off the motors. While this process should not be harmful to the controller, it may be to the power supply, unless one or more of the protective steps below is taken:

• Use a power supply that will not suffer damage in case a voltage is applied at its

output that is higher than the transformer’s own output voltage. This information is seldom published in commercial power supplies, so it is not always possible to obtain positive reassurance that the supply will survive such a condition.

• Avoid deceleration that is quicker than the natural deceleration due to the friction in

the motor assembly (motor, gears, load). Any deceleration that would be quicker than natural friction means that braking energy will need to be taken out of the system, causing a reverse current flow and voltage rise. See “Programmable Acceleration” on page 47.

• Place a battery in parallel with the power supply output. This will provide a reservoir

into which regeneration current can flow. It will also be very helpful for delivering high current surges during motor acceleration, making it possible to use a lower current power supply. Batteries mounted in this way should be connected for the first time only while fully charged and should not be allowed to discharge. The power supply will be required to output unsafe amounts of current if connected directly to a discharged battery. Consider using a decoupling diode on the power supply’s output to prevent battery or regeneration current to flow back into the power supply.

• Place a resistive load in parallel with the power supply, with a circuit to enable that

load during regeneration. This solution is more complex but will provide a safe path for the braking energy into a load designed to dissipate it. To prevent current from flowing from the power supply into the load during normal operation, an active switch would enable the load when the voltage rises above the nominal output of the power supply.

AX2550 Motor Controller User’s Manual 39

Connecting Power and Motors to the Controller

40 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Basic Operation

SECTION 5 General

Operation

This section discusses the controller’s normal operation in all its supported operating modes.

Basic Operation

The AX2550’s operation can be summarized as follows:

• Receive commands from a radio receiver, joystick or a microcomputer

• Activate the motors according to the received command

• Perform continuous check of fault conditions and adjust actions accordingly

Multiple options are available for each of the above listed functions which can be combined to produce practically any desired mobile robot configuration.

Input Command Modes

The controller will accept commands from one of the following sources

• R/C radio

• Serial data (RS232)

• Analog signal (0 to 5V)

A detailed discussion on each of these modes and the available commands is provided in the following dedicated chapters: “R/C Operation” on page 109, “Serial (RS-232) Controls and Operation” on page 131, and “Analog Control and Operation” on page 123.

The controller’s factory default mode is R/C radio. The mode can be changed using any of the methods described in “Programming using built-in Switches and Display” on page 171 and “Loading, Changing Controller Parameters” on page 181.

AX2550 Motor Controller User’s Manual 41

General Operation

Selecting the Motor Control Modes

For each motor, the AX2550 supports multiple motion control modes. The controller’s fac- tory default mode is Open Loop Speed control for each motor. The mode can be changed using any of the methods described in “Programming using built-in Switches and Display” on page 171 and “Loading, Changing Controller Parameters” on page 181.

Open Loop, Separate Speed Control

In this mode, the controller delivers an amount of power proportional to the command information. The actual motor speed is not measured. Therefore the motors will slow down if there is a change in load as when encountering an obstacle and change in slope. This mode is adequate for most applications where the operator maintains a visual contact with the robot.

In the separate speed control mode, channel 1 commands affect only motor 1, while channel 2 commands affect only motor 2. This is illustrated in Figure 15 below.

Controller

FIGURE 15. Examples of effect of commands to motors in separate mode

Open Loop, Mixed Speed Control

This mode has the same open loop characteristics as the previously described mode. However, the two commands are now mixed to create tank-like steering when one motor is used on each side of the robot: Channel 1 is used for moving the robot in the forward or reverse direction. Channel 2 is used for steering and will change the balance of power on each side to cause the robot to turn.

Figure 16 below illustrates how the mixed mode works.

42 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Selecting the Motor Control Modes

Controller

FIGURE 16. Effect of commands to motors examples in mixed mode

Closed Loop Speed Control

In this mode, illustrated in Figure 18, an analog tachometer or an optical encoder (AX2850 only) is used to measure the actual motor speed. If the speed changes because of changes in load, the controller automatically compensates the power output. This mode is preferred in precision motor control and autonomous robotic applications. Details on how to wire the tachometer can be found in “Connecting Tachometer to Analog Inputs” on page 64. Closed Loop Speed control operation is described in “Closed Loop Speed Mode” on page 97.

FIGURE 17. Motor with tachometer or Encoder for Closed Loop Speed operation

Close Loop Position Control

In this mode, illustrated in Figure 18, the axle of a geared down motor is coupled to a potentiometer that is used to compare the angular position of the axle versus a desired position. This AX2550 feature makes it possible to build ultra-high torque “jumbo servos” that can be used to drive steering columns, robotic arms, life-size models and other heavy loads. Details on how to wire the position sensing potentiometers and operating in this mode can be found in “Closed Loop Position Mode” on page 85.

AX2550 Motor Controller User’s Manual 43

General Operation

Position Sensor

Gear box

FIGURE 18. Motor with potentiometer assembly for Position operation

User Selected Current Limit Settings

The AX2550 has current sensors at each of its two output stages. Every 16 ms, this current is measured and a correction to the output power level is applied if higher than the user preset value.

Position Feedback

The current limit may be set using the controller’s switches or the supplied PC utility. Using the switches, 7 limits may be selected as shown in the table below.

TABLE 4. Current limit settings using the switches

Setting Continuous High Amps

030A

145A

260A

375A

490A

5 - default 105A

6120A

Using the PC utility is it possible to set the limit with a 1A granularity from 15A to 120A

During normal operation, current limiting is further enhanced by the techniques described in the following sections.

Temperature-Based Current Limitation

The AX2550 features active current limitation that uses a combination of a user defined preset value (discussed above) which in turn may be reduced automatically based on measured operating temperature. This capability ensures that the controller will be able to work safely with practically all motor types and will adjust itself automatically for the various load conditions.

44 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Battery Current vs. Motor Current

When the measured temperature reaches 80oC, the controller’s maximum current limit begins to drop to reach 0A at 100oC. Above 100oC, the controller’s power stage turns itself off completely.

TABLE 5. Effect of Case temperature on Max Amps Limit

Temperature Max Amps

Below 80 oC 120A

80 oC 120A

85 oC 80A

90 oC 40A

95 oC 20A

100 oC 0

Above 100 oC Both Power Stages OFF

The numbers in the table are the max Amps allowed by the controller at a given temperature point. If the Amps limit is manually set to a lower value, then the controller will limit the current to the lowest of the manual and temperature-adjusted max values.

This capability ensures that the controller will be able to work safely with practically all motor types and will adjust itself automatically for the various load and environmental conditions. The time it takes for the heat sink’s temperature to rise depends on the current output, ambient temperature, and available air flow (natural or forced).

Note that the measured temperature is measured on the heat sink near the Power Transistors and will rise and fall faster than the outside surface.

Battery Current vs. Motor Current

The controller measures and limits the current that flows from the battery. Current that flows through the motor is typically higher. This counter-intuitive phenomenon is due to the “flyback” current in the motor’s inductance. In some cases, the motor current can be extremely high, causing heat and potentially damage while battery current appears low or reasonable.

The motor’s power is controlled by varying the On/Off duty cycle of the battery voltage 16,000 times per second to the motor from 0% (motor off) to 100 (motor on). Because of the flyback effect, during the Off time current continues to flow at nearly the same peak and not the average - level as during the On time. At low PWM ratios, the peak current and therefore motor current - can be very high as shown in Figure 20, “Instant and average current waveforms,” on page 46.

The relation between Battery Current and Motor current is given in the formula below:

Motor Current = Battery Current / PWM ratio

Example: If the controller reports 10A of battery current while at 10% PWM, the current in the motor is 10 / 0.1 = 100A.

AX2550 Motor Controller User’s Manual 45

General Operation

FIGURE 19. Current flow during operation

Vbat

Motor

Off

FIGURE 20. Instant and average current waveforms

The relation between Battery Current and Motor current is given in the formula below:

Motor Current = Battery Current / PWM Ratio

Example: If the controller reports 10A of battery current while at 10% PWM, the current in the motor is 10 / 0.1 = 100A.

Important Warning

Do not connect a motor that is rated at a higher current than the controller. While the battery current will never exceed the preset Amps limit, that limit may be reached at a PWM cycle lower than 100% resulting in a higher and potentially unsafe level through the motor and the controller.

Off

I mot Avg

I bat Avg

Regeneration Current Limiting

The AX2550’s current sensor is capable of measuring current in the reverse flow (regeneration). Using this capability, the controller will automatically relax the braking effect of the power output stage to keep the regeneration current within safe values. Because of the controller’s high current handling capabilities, this protection mechanism activates only when abrupt deceleration are applied to high-inertia, ultra-low impedance motors.

46 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Programmable Acceleration

When changing speed command, the AX2550 will go from the present speed to the desired one at a user selectable acceleration. This feature is necessary in order to minimize the surge current and mechanical stress during abrupt speed changes.

This parameter can be changed by using the controller’s front switches or using serial com- mands. When configuring the controller using the switches (see “Configuring the Controller using the Switches” on page 171), acceleration can be one of 6 available preset values, from very soft(0) to very quick (6). The AX2550’s factory default value is medium soft (2).

When using the serial port, acceleration can be one of 24 possible values, selectable using the Roborun utility or entering directly a value in the MCU’s configuration EEPROM. Table 6 shows the corresponding acceleration for all Switch and RS232 settings.

Numerically speaking, each acceleration value corresponds to a fixed percentage speed increment, applied every 16 milliseconds. The value for each setting is shown in the table below.

TABLE 6. Acceleration setting table

Acceleration Setting Using RS232

30 Hex 0.78% 2.05 seconds

20 Hex 1.56% 1.02 seconds

10 Hex 2.34% 0.68 second

00 Hex 0 3.13% 0.51 second

31 Hex 3.91% 0.41 second

21 Hex 4.69% 0.34 second

11 Hex 5.47% 0.29 second

01 Hex 1 6.25% 0.26 second

32 Hex - 7.03% 0.23 second

22 Hex - 7.81% 0.20 second

12 Hex - 8.59% 0.19 second

02 Hex 2 (default) 9.38% 0.17 second

33 Hex - 10.16% 0.16 second

23 Hex - 10.94% 0.15 second

13 Hex - 11.72% 0.14 second

03 Hex 3 12.50% 0.128 second

34 Hex - 13.28% 0.120 second

24 Hex - 14.06% 0.113 second

14 Hex - 14.84% 0.107 second

04 Hex 4 15.63% 0.102 second

35 Hex - 16.41% 0.097 second

25 Hex - 17.19% 0.093 second

Acceleration Setting Using Switches

%Acceleration per 16ms

Time from 0 to max speed

AX2550 Motor Controller User’s Manual 47

General Operation

TABLE 6. Acceleration setting table

Acceleration Setting Using RS232

15 Hex - 17.97% 0.089 second

05 Hex 5 18.75% 0.085 second

When configuring the acceleration parameter using the Roborun utility, four additional acceleration steps can be selected between the six ones selectable using the switch, extending the slowest acceleration to 2.04 seconds from 0 to max speed. See “Power Settings” on page 182 for details on how to configure this parameter using Roborun.

Acceleration Setting Using Switches

%Acceleration per 16ms

Time from 0 to max speed

Important Warning

Depending on the load’s weight and inertia, a quick acceleration can cause consider- able current surges from the batteries into the motor. A quick deceleration will cause an equally large, or possibly larger, regeneration current surge. Always experiment with the lowest acceleration value first and settle for the slowest acceptable value.

Command Control Curves

The AX2550 can also be set to translate the joystick or RS232 motor commands so that the motors respond differently whether or not the joystick is near the center or near the extremes.

The controller can be configured to use one of 5 different curves independently set for each chan nel.

The factory default curve is a “linear” straight line, meaning that after the joystick has moved passed the deadband point, the motor’s speed will change proportionally to the joystick position.

Tw o “exponential’ curves, a weak and a strong, are supported. Using these curves, and after the joystick has moved past the deadband, the motor speed will first increase slowly, increasing faster as the joystick moves near the extreme position. Exponential curves allow better control at slow speed while maintaining the robot’s ability to run at maximum speed.

Tw o “logarithmic” curves, a weak and a strong, are supported. Using these curves, and after the joystick has moved past the deadpoint, the motor speed will increase rapidly, and then increase less rapidly as the joystick moves near the extreme position.

The graph below shows the details of these curves and their effect on the output power as the joystick is moved from its center position to either extreme. The graph is for one joystick only. The graph also shows the effect of the deadband setting.

48 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Left / Right Tuning Adjustment

% Forward (Motor Output)

100

- 60

- 80

- 100

FIGURE 21. Exponentiation curves

The AX2550 is delivered with the “linear” curves selected for both joystick channels. To select different curves, the user will need to change the values of “E” (channel 1) and “F” (channel 2) according to the table below. Refer to the chapter “Configuring the Controller using the Switches” on page 171 or “Using the Roborun Configuration Utility” on page 177 for instructions on how to program parameters into the controller.

- 40

- 20

100

% Reverse

Logarithmic Strong

Logarithmic Weak

Linear (default)

Exponential Weak

Exponential Strong

% Command Input

100

Deadband

TABLE 7. Exponent selection table

Exponentiation Parameter Value Selected Curve

E or F = 0 Linear (no exponentiation) - default value

E or F = 1 strong exponential

E or F = 2 normal exponential

E or F = 3 normal logarithmic

E or F = 4 strong logarithmic

Left / Right Tuning Adjustment

By design, DC motors will run more efficiently in one direction than the other. In most situations this is not noticeable. In others, however, it can be an inconvenience. When operating in open loop speed control, the AX2550 can be configured to correct the speed in one direction versus the other by as much as 10%. Unlike the Joystick center trimming tab that

AX2550 Motor Controller User’s Manual 49

General Operation

is found on all R/C transmitters, and which is actually an offset correction, the Left/Right Adjustment is a true multiplication factor as shown in Figure 22

% Forward (Motor Output)

100

- 20

- 40

- 60

- 80

- 100

100

% Reverse

% Forward (Motor Output)

FIGURE 22. Left Right adjustment curves

The curves on the left show how a given forward direction command value will cause the motor to spin 3 or 5.25% slower than the same command value applied in the reverse direction. The curves on the right show how the same command applied to the forward direction will case the motor to spin 3 to 5.25% faster than the same command applied in the reverse direction. Note that since the motors cannot be made to spin faster than 100%, the reverse direction is the one that is actually slowed down.

-3%

-5.25%

% Command Input

100

5.25%

- 100

% Forward (Motor Output)

100

- 20

- 40

- 60

- 80

100

% Reverse

100

In applications where two motors are used in a mixed mode for steering, the Left/Right Adjustment parameter may be used to make the robot go straight in case of a natural tendency to steer slightly to the left or to the right.

The Left/Right adjustment parameter can be set from -5.25% to +5.25% in seven steps of

0.75%. See “Programmable Parameters List” on page 174 and “Loading, Changing Controller Parameters” on page 181 for details on how to adjust this parameter.

The Left/Right adjustment is performed in addition to the other command curves described in this section. This adjustment is disabled when the controller operates in any of the supported closed loop modes.

TABLE 8. Left/Right Adjustment Parameter selection

Parameter Value Speed Adjustment Parameter Value Speed Adjustment

7 None (default)

0 -5.25% 8 0.75%

1-4.5%91.5%

2 -3.75% 10 2.25%

3 -3% 11 3%

4 -2.25% 12 3.75%

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Activating Brake Release or Separate Motor Excitation

TABLE 8. Left/Right Adjustment Parameter selection

Parameter Value Speed Adjustment Parameter Value Speed Adjustment

5 -1.5% 12 4.5%

6 -0.75% 14 5.25%

Activating Brake Release or Separate Motor Excitation

The controller may be configured so that the Output C will turn On whenever one of the two motors is running. This feature is typically used to activate the mechanical brake release sometimes found on motors for personal mobility systems. Likewise, this output can be used to turn on or off the winding that creates the armature’s magnetic field in a separate excitation motor. This function is disabled by default and may be configured using the Roborun PC utility. See “Loading, Changing Controller Parameters” on page 181. See “Connecting devices to Output C” on page 59 for details on how to connect to the output.

Emergency Shut Down Using Controller Switches

In case of emergency, it is possibly to cause the controller to cut off the power to the motors by depressing the Program and Set buttons simultaneously as shown in the figure below. The controller will stop immediately without delay.

Program Set

Press the two buttons simultaneously to cause an emergency stop

FIGURE 23. Activating an Emergency Stop

After and Emergency Stop condition, the controller must be reset or powered Off and On to resume normal operation.

Reset

Emergency Stop using External Switch

An external switch can be added to the AX2550 to allow the operator to stop the controller’s output in case of emergency. This controller input can be configured as the “Inverted” detection instead of Emergency Stop. The factory default for this input is “No Action”.

AX2550 Motor Controller User’s Manual 51

General Operation

Inverted Operation

The switch connection is described in “Connecting Switches or Devices to EStop/Invert Input” on page 62. The switch must be such that it is in the open state in the normal situation and closed to signal an emergency stop command.

After and Emergency Stop condition, the controller must be reset or powered Off and On to resume normal operation.

For robots that can run upside-down, the controller can be configured to reverse the motor commands using a gravity activated switch when the robot is flipped. This feature is enabled only in the mixed mode and when the switch is enabled with the proper configuration of the “Input switch function” parameter. See “Programmable Parameters List” on page 174.

The switch connection is described in “Connecting Switches or Devices to EStop/Invert Input” on page 62. The switch must be such that it is in the open state when the robot is in the normal position and closed when inverted. When the status of the switch has changed, the controller will wait until the new status has remained stable for 0.5s before acknowledging it and inverting the commands. This delay is to prevent switch activation triggered by hits and bounces which may cause the controller to erroneously invert the commands.

Special Use of Accessory Digital Inputs

The AX2550 includes two general purpose digital inputs identified as Input E and Input F. When an Encoder Module is installed, input E is disabled. The location of these inputs on the DB15 connector can be found in the section “I/O List and Pin Assignment” on page 58, while the electrical signal needed to activate them is shown on “Connecting Switches or Devices to Input F” on page 61.

By default, these inputs are ignored by the controller. However, the AX2550 may be configured to cause either of the following actions:

• Activate the buffered Output C

• Turn Off/On the power MOSFET transistors

These alternate modes can only be selected using the Roborun Utility (see “Control Settings” on page 181. Each of these modes is detailed below.

Using the Inputs to Activate the Buffered Output

When this setting is selected, the buffered Output C will be On when the Input line is pulled to Ground (0V). The Output will be Off when the Input is pulled high.

This function makes it possible to drive solenoids or other accessories up to 2A at 24V using a very low current switch, for example.

Using the Inputs to turn Off/On the Power MOSFET transistors

When this setting is selected, the controller’s Power MOSFET transistors will be active, and the controller will be operating normally, only when the input is pulled to ground.

52 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

When the input is pulled high, all the power MOSFETs are turned Off so that the motors are effectively disconnected from the controller.

This function is typically used to create a “dead man switch” when the controller is driven using an analog joystick. The motors will be active only while the switch is depressed. If the switch is left off for any reason, the motors will be disconnected and allowed to freewheel rather than coming to an abrupt stop.

Self-Test Mode

The AX2550 incorporates a simple Self-Test mode that performs the following functions:

The Self Test mode can be conveniently initiated using only the controller’s switches so that no radio or computer is needed.

To enter the Self Test mode, press and hold the Set button while resetting or powering up the controller.

Self-Test Mode

• Display the software revision number on the LED display

• Ramp each motor up and down in both directions

• Internal parameters on the serial port output

After a few seconds, the LEDs will display a sequence of two numerical digits and an optional letter separated by dashes as shown in the examples below.

= Software version 1.9b

FIGURE 25. Press and hold “Set” to display version number and enter self-test

After these digits are displayed, the controller will attempt to power the motors. Motor 1 will be ramped from stop to full speed forward to full speed reverse and back to stop. Then the same operation will repeat on motor 2. After both motors have completed their ramps, the software revision will be displayed again and the motors will be ramped again. This sequence will repeat itself indefinitely until the controller is powered off or reset.

While in the Self Test mode, the AX2550 will continuously send a string of characters on the RS232 output line. This string will contain 12 or 13 two-digits hexadecimal number representing the 13 following operating parameters.

• Captured R/C Command 1 and 2

• Power Applied to Controller’s output stage

• Values applied to Analog inputs 1 and 2

• Amps on channel 1 and 2

• Internal Heat Sink temperatures 1 and 2

• Main Battery voltage

• Internal 12V voltage

AX2550 Motor Controller User’s Manual 53

General Operation

The entire string is repeated every 208 or 224 milliseconds (depending whether the encoder module is present) with the latest internal parameter values. This information can be logged using the Roborun Utility (see “Viewing and Logging Data in Analog and R/C Modes” on page 192).

The string and data format is described in “Analog and R/C Modes Data Logging String For- mat” on page 166.

Important Warning

Disconnect the Motor Power (thick red wires) from the battery and power the controller by applying 12V on the Power Control input if you do not wish the motors to be activated while in Self Test mode.

This could be the case if you only wish to use the Self Test sequence to read the software revision number or to monitor the joystick capture.

• Encoder Speed or Position if module is installed

54 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

AX2550 Connections

SECTION 6 Connecting

Sensors and Actuators to Input/Outputs

This section describes the various inputs and outputs and provides guidance on how to connect sensors, actuators or other accessories to them.

AX2550 Connections

The AX2550 uses a set of power wires (located on the back of the unit) and a DB15 connector for all necessary connections. The diagram on the figure below shows a typical wiring diagram of a mobile robot using the AX2550 controller.

The wires are used for connection to the batteries and motors and will typically carry large current loads. Details on the controller’s power wiring can be found at “Connecting Power and Motors to the Controller” on page 29

The DB15 connector is used for all low-voltage, low-current connections to the Radio, Microcontroller, sensors and accessories. This section covers only the connections to sensors and actuators.

For information on how to connect the R/C radio or the RS232 port, see “R/C Operation” on page 109 and “Serial (RS-232) Controls and Operation” on page 131.

AX2550 Motor Controller User’s Manual 55

Connecting Sensors and Actuators to Input/Outputs

t e

gram

1- DC Motors

2- Optional sensors:

- Tachometers (Closed loop Speed mode)

- Potentiometers (Servo mode)

- Optical Encoder (AX2850 only - all closed loop modes)

3- Motor Power supply wires

4- Power Control wire

FIGURE 26. Typical controller connections

56 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

5- Controller

6- R/C Radio Receiver, microcomputer, or

wireless modem

7- Command: RS-232, R/C Pulse

8- Miscellaneous I/O

9- Running Inverted, or emergency stop

switch

AX2550’s Inputs and Outputs

In addition to the RS232 and R/C channel communication lines, the AX2550 includes several inputs and outputs for various sensors and actuators. Depending on the selected operating mode, some of these I/Os provide feedback and/or safety information to the controller.

When the controller operates in modes that do not use these I/O, these signals become available for user application. Below is a summary of the available signals and the modes in which they are used by the controller or available to the user.

TABLE 9. AX2550 IO signals and definitions

Signal I/O type Use Activated

Out C 2A Digital Output User

defined

Inp F Digital Input User

defined

Activate Output C

Turn FETs On/Off

Inp E Digital Input Same as Input F - (Not available when encoder module present)

EStop/Invert Digital Input Emer-

gency stop

Invert Controls

User defined

Analog In 1 Analog Input Tachome-

ters input

Position sensing

User defined

Analog In 2 Analog Input 2 Same as Analog 1 but for Channel 2

Analog In 3 Analog Input 3 Position

sensing

User defined

Analog In 4 Analog Input 4 Same as Analog 3 but for Channel 4

Activated using R/C channel 3 (R/C mode), or serial command (RS232 mode)

Activated when any one motor is powered (when enabled)

Active in RS232 mode only. Read with serial command (RS232)

When Input is configured to drive Output C

When Input is configured as “dead man switch” input

When Input is configured as Emergency Stop switch input.

When Input is configured as Invert Controls switch input.

When input is configured as general purpose. Read with serial command (RS232).

When Channel 1 is configured in Closed Loop Speed Control with Analog feedback

When Channel 1 is configured in Closed Loop Position Control with RC or RS232 command and Analog feedback

Read value with serial command (RS232).

When Channel 1 is configured in Closed Loop Position Control with Analog command and Analog feedback

Read value with serial command (RS232).

AX2550 Motor Controller User’s Manual 57

Connecting Sensors and Actuators to Input/Outputs

I/O List and Pin Assignment

The figure and table below lists all the inputs and outputs that are available on the AX2550.

Pin1

FIGURE 27. Controller’s DB15 connector pin numbering

TABLE 10. DB15 connector pin assignment

Pin Number

1 and 9 Output Output C 2A Accessory Output C

2Output

3 Input

4 Input

5 and 13 Power Out Ground Controller ground (-)

6 GND In

Input or Output

Unused in RevB Hardware

Signal depending on Mode Description

R/C: Data Out RS232 Data Logging Output

RS232: Data Out RS232 Data Out

Analog: Data Out RS232 Data Logging Output

R/C: Ch 1 R/C radio Channel 1 pulses

RS232: Data In RS232 Data In (from PC/MCU)

Analog: Unused Unused

R/C: Ch 2 R/C radio Channel 2 pulses

RS232/Analog: Input F Digital Input F readable RS232 mode

Dead man switch activation

Ground

Unused in RevB Hardware

Optocoupler GND Input, Connect to pin 5**

Unused in RevB Hardware

58 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Connecting devices to Output C

TABLE 10. DB15 connector pin assignment

Pin Number

7+5V In

8 Digital In

10 Ana l og i n

11 Analog in RC/RS232: Ana in 1 Channel 1 speed or position feedback input

12 RC: Unused

14 Power Out +5V +5V Power Output (100mA max.)

15 Input Input EStop/Inv Emergency Stop or Invert Switch input

Input or Output

Unused in RevB Hardware

and Analog In

Signal depending on Mode Description

+5V

Unused in RevB Hardware

R/C: Ch 3 R/C radio Channel 3 pulses - (Not available on

RS232: Input E / Ana in 4Accessory input E

Ana: Input E / Ana in 4 Accessory input E

RC/RS232: Ana in 2 Channel 2 speed or position feedback input

Analog: Command 2 Analog command for channel 2

Analog: Command 1 Analog command for channel 1

RS232: Ana in 3 Analog input 3

Ana: Ana in 3 Channel 1 speed or position feedback input in

Optocoupler +5V Input. Connect to pin 14**

Unused in RevB Hardware

AX2850)

Dead man Switch Input Activate Output C Analog Input 4 in RevB Hardware

Dead man Switch Input Activate Output C Channel 2 speed or position feedback input in RevB Hardware

RevB Hardware

**These connections should only be done in RS232 mode or R/C mode with radio powered from the controller.

Connecting devices to Output C

Output C is a buffered, Open Drain MOSFET output capable of driving over 2A at up to 24V.

The diagrams on Figure 28 show how to connect a light or a relay to this output:

AX2550 Motor Controller User’s Manual 59

Connecting Sensors and Actuators to Input/Outputs

Relay, Valve Motor, Solenoid or other Inductive Load

Lights, LEDs, or any other non-inductive load

5 to 24V DC

Output C 1,9

Ground 5

Internal Transistor

FIGURE 28. Connecting inductive and resistive loads to Output C

This output can be turned On and Off using the Channel 3 Joystick when in the R/C mode. See “Activating the Accessory Outputs” on page 120 for more information.

When the controller is used in RS232 mode, this output can be turned On and Off using the !C (On) and !c (Off) command strings. See “Controller Commands and Queries” on page 138 for more information.

Important warning:

Overvoltage spikes induced by switching inductive loads, such as solenoids or relays, will destroy the transistor unless a protection diode is used.

5 to 24V DC

Output C 1,9

Ground 5

Internal Transistor

Connecting Switches or Devices to Input E

Input E is a general purpose, digital input. This input is only available if no encoder module is present and is active when in the RS232 and Analog modes. In R/C mode, this line is used as the radio channel 3 input.

60 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Connecting Switches or Devices to Input F

Input E is a high impedance input with a pull-up resistor built into the controller. Therefore it will report an On state if unconnected, and a simple switch as shown on Figure 29 is necessary to activate it.

+5V Out 14

50kOhm

Input E 8

10kOhm

50kOhm

Ground 5

FIGURE 29. Switch wirings to Input E

The status of Input E can be read in the RS232 mode with the ?i command string. The controller will respond with three sets of 2 digit numbers. The status of Input E is contained in the first set of numbers and may be 00 to indicate an Off state, or 01 to indicate an On state.

This input is not available on the AX2850 or on the AX2550 with the Encoder Module installed.

Remember that, in RevB hardware, InputE is shared with the Analog Input 4. If an analog sensor is connected, the controller will return a Digital value of 0 if the voltage is lower than 0.5V and a value of 1 if higher

Connecting Switches or Devices to Input F

Input F is a general purpose digital input. This input is only active when in the RS232 or Analog modes. In R/C mode, this line is used as the radio channel 2 input.

Internal Buffer

When left open, Input F is in an undefined stage. As shown in the figure below, a pull down or pull up resistor must be inserted when used with a single pole switch. The resistor may be omitted when used with a dual pole switch.

AX2550 Motor Controller User’s Manual 61

Connecting Sensors and Actuators to Input/Outputs

On controllers prior to RevB, Input F is an opto-coupled input and requires the buffer to be powered with a connection between pin 14 and 7, and between 13 and 6, to operate.This power connection in not needed on RevB hardware.

+5V Out 14

+5V In 7

10kOhm

+5V In 7

Input F 4

GND In 6

GND Out 5

10kOhm

Internal

Internal Buffer

Buffer

FIGURE 30. Switch wiring to Input F

The status of Input F can be read in the RS232 mode with the ?i command string. The controller will respond with three sets of 2 digit numbers. The status of Input F is contained in the second set of numbers and may be 00 to indicate an Off state, or 01 to indicate an On state.

10kOhm

+5V Out 14

+5V In 7

Input F 4

GND In 6

GND Out 5

10kOhm

Internal

Internal Buffer

Buffer

Connecting Switches or Devices to EStop/Invert Input

This input is used to connect various switches or devices depending on the selected controller configuration.

The factory default for this input is “No Action”.

This input can also be configured to be used with an optional “inverted” sensor switch. When activated, this will cause the controls to be inverted so that the robot may be driven upside-down.

When neither Emergency Stop or Inverted modes are selected, this input becomes a general purpose input like the other two described above.

This input is a high impedance input with a pull-up resistor built into the controller. Therefore it will report an On state (no emergency stop, or not inverted) if unconnected. A simple switch as shown on Figure 31 is necessary to activate it. Note that to trigger an Emergency Stop, or to detect robot inversion this input must be pulled to ground. Figure 31 show how to wire the switch to this input.

62 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Analog Inputs

+5V 14

Input EStop/Inv 15

Ground 5

FIGURE 31. Emergency Stop / Invert switch wiring

The status of the EStop/Inv can be read at all times in the RS232 mode with the ?i com- mand string. The controller will respond with three sets of 2 digit numbers. The status of the ES/Inv Input is contained in the last set of numbers and may be 00 to indicate an Off state, or 01 to indicate an On state.

AX2500 Internal Buffer and Resistor

10kOh m

Analog Inputs

The controller has (2 on pre-RevB hardware) 4 Analog Inputs that can be used to connect position, speed, temperature, voltage or most other types of analog sensors. These inputs can be read at any time using the ?p query for Analog inputs 1 and 2 and the ?r query for Inputs 3 and 4. The following section show the various uses for these inputs.

Connecting Position Potentiometers to Analog Inputs

When configured in the Position mode, the controller’s analog inputs are used to obtain position information from a potentiometer coupled to the motor axle. This feature is useful in order to create very powerful servos as proposed in the figure below:

Position Feedback

Potentiometer

Gear box

FIGURE 32. Motor and potentiometer assembly for position servo operation

AX2550 Motor Controller User’s Manual 63

Connecting Sensors and Actuators to Input/Outputs

Connecting the potentiometer to the controller is as simple as shown in the diagram on Figure 33.

+5V 14

Ana 1: 11 Ana 2: 10 Ana 3: 12

Ana 4: 8

10kOhm

Ground 5

FIGURE 33. Potentiometer wiring in Position mode

The potentiometer must be attached to the motor frame so that its body does not move in relationship with the motor. The potentiometer axle must be firmly connected to the gear box output shaft. The gearbox must be as tight as possible so that rotation of the motor translates into direct changes to the potentiometers, without slack, at the gearbox’s out- put.

Internal Resistors and Converter

47kOhm

10kOhm

47kOhm

A/D

TABLE 11. Analog Position Sensor connection depending on operating mode

Operating Mode

Ana 1 pin 11

Ana2 pin 10

Ana 3 pin 12

Ana 4 pin 8

RC or RS232 - Dual Channel Position 1 Position 2 Unused Unused

Analog - Dual Channel Command 1 Command 2 Position 1 Position 2

RC or RS232 - Single Channel Position Unused Unused Unused

RC or RS232 - Dual Channel Command Unused Position Unused

See “Closed Loop Position Mode” on page 85 for complete details on Position Mode wir- ing and operation.

Important Warning

Beware that the wrong + and - polarity on the potentiometer will cause the motor to turn in the wrong direction and not stop. The best method to figure out the right potentiometer is try one way and change the polarity if incorrect. Note that while you are doing these tests, the potentiometer must be loosely attached to the motor’s axle so that it will not be forced and broken by the motor’s uncontrolled rotation in case it was wired wrong.

Connecting Tachometer to Analog Inputs

When operating in closed loop speed mode, tachometers must be connected to the controller to report the measured motor speed. The tachometer can be a good quality brushed DC motor used as a generator. The tachometer shaft must be directly tied to that of the motor with the least possible slack.

64 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Connecting Tachometer to Analog Inputs

Since the controller only accepts a 0 to 5V positive voltage as its input, the circuit shown in Figure 34 must be used between the controller and the tachometer: a 10kOhm potentiometer is used to scale the tachometer output voltage to -2.5V (max reverse speed) and +2.5V (max forward speed). The two 1kOhm resistors form a voltage divider that sets the idle voltage at mid-point (2.5V), which is interpreted as the zero position by the controller. The voltage divider resistors should be of 1% tolerance or better. To precisely adjust the

2.5V midpoint value it is recommended to add a 100 ohm trimmer on the voltage divider.

With this circuitry, the controller will see 2.5V at its input when the tachometer is stopped, 0V when running in full reverse, and +5V in full forward.

+5V 14

1kOhm

Zero Adjust 100 Ohm pot

1kOhm

Max Speed Adjust 10kOhm pot

Ta c h

Ana 1: 11 Ana 2: 10 Ana 3: 12 Ana 4: 8

Ground 5

Internal Resistors and Converter

47kOhm

A/D

10kOhm

47kOhm

FIGURE 34. Tachometer wiring diagram

The tachometers can generate voltages in excess of 2.5 volts at full speed. It is important, therefore, to set the potentiometer to the minimum value (cursor all the way down per this drawing) during the first installation.

Since in closed loop control the measured speed is the basis for the controller’s power out- put (i.e. deliver more power if slower than desired speed, less if higher), an adjustment and calibration phase is necessary. This procedure is described in “Closed Loop Speed Mode”

on page 97.

TABLE 12. Analog Speed Sensor connection depending on operating mode

Operating Mode Ana 1 (p11) Ana2 (p10) Ana 3 (p12) Ana 4 (p8)

RC or RS232 - Dual Channel Speed 1 Speed 2 Unused Unused

Analog - Dual Channel Command 1 Command 2 Speed 1 Speed 2

RC or RS232 - Single Channel Speed Unused Unused Unused

RC or RS232 - Dual Channel Command Unused Speed Unused

Important Warning

The tachometer’s polarity must be such that a positive voltage is generated to the controller’s input when the motor is rotating in the forward direction. If the polarity is inverted, this will cause the motor to run away to the maximum speed as soon as the controller is powered with no way of stopping it other than pressing the emergency stop button or disconnecting the power.

AX2550 Motor Controller User’s Manual 65

Connecting Sensors and Actuators to Input/Outputs

Connecting External Thermistor to Analog Inputs

Using external thermistors, the AX2550 can be made to supervise the motor’s tempera- ture and adjust the power output in case of overheating. Connecting thermistors is done according to the diagram show in Figure 35. The AX2550 is calibrated using a 10kOhm Negative Coefficient Thermistor (NTC) with the temperature/resistance characteristics shown in the table below.

TABLE 13. Recommended NTC characteristics

Temp (oC) -25 0 25 50 75 100

Resistance (kOhm) 86.39 27.28 10.00 4.16 1.92 0.93

+5V 14

Ana 1: 11

10kOhm

NTC

Thermistor

Ana 2: 10 Ana 3: 12 Ana 4: 8

47kOhm

Internal Resistors and Converter

A/D

10kOhm

Ground 5

FIGURE 35. NTC Thermistor wiring diagram

Thermistors are non-linear devices. Using the circuit described on Figure 35, the controller will read the following values (represented in signed binary) according to the temperature.

100

-50

Analog Input Reading

-100

-150

-20

-10

Temperature in Degrees C

FIGURE 36. Signed binary reading by controller vs. NTC temperature

100

110

66 AX2550 Motor Controller User’s Manual Version 1.9b. June 1, 2007

Using the Analog Inputs to Monitor External Voltages

To read the temperature, use the ?p command to have the controller return the A/D converter’s value. The value is a signed 8-bit hexadecimal value. Use the chart data to convert the raw reading into a temperature value.

Using the Analog Inputs to Monitor External Voltages

The analog inputs may also be used to monitor the battery level or any other DC voltage. In this mode, the controller does not use the voltage information but merely makes it available to the host microcomputer via the RS232 port. The recommended schematic is shown in Figure 37.

To Battery + Terminal

47kOhm

4.7kOhm

+5V 14

Ana 1: 11 Ana 2: 10 Ana 3: 12 Ana 4: 8

Ground 5

FIGURE 37. Battery voltage monitoring circuit

Using these resistor values, it is possible to measure a voltage ranging from -5V to +60V with a 0.25V resolution. The formula for converting the A/D reading into a voltage value is as follows.

Measured volts = ((controller reading + 128) * 0.255) -5

Note: The A/D converter’s reading is returned by the ?p command and is a signed 8-bit hexadecimal value. You must add 128 to bring its range from -127/+127 to 0/255.

Connecting User Devices to Analog Inputs

Internal Resistors and Converter

47kOhm

A/D

10kOhm

47kOhm

The two analog inputs can be used for any other purpose. The equivalent circuit for each input is shown in Figure 38. The converter operates with an 8-bit resolution, reporting a value of 0 at 0V and 255 at +5V. Care should be taken that the input voltage is always positive and does not exceed 5V. The converter’s intrinsic diodes will clip any negative voltage or voltage above 5V, thus providing limited protection. The value of the analog inputs can be read through the controller’s RS232 port.

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Connecting Sensors and Actuators to Input/Outputs

+5V 14

Ana 1: 11

Ana 2: 10 Ana 3: 12 Ana 4: 8

Ground 5

47kOhm

FIGURE 38. AX2550 Analog Input equivalent circuit

Internal Voltage Monitoring Sensors

The AX2550 incorporates voltage sensors that monitor the Main Battery voltage and the Internal 12V supply. This information is used by the controller to protect it against overvoltage and undervoltage conditions (see “Overvoltage Protection” on page 38 and “Under- voltage Protection” on page 38). These voltages can also be read from the RS232 serial port using the ?e query.

The returned value are numbers ranging from 0 to 255. To convert these numbers into a Voltage figure, the following formulas must be used:

Measured Main Battery Volts = 55 * Read Value / 256

Measured Internal Volts = 28.5 * Read Value / 256

A/D

10kOhm

Internal Heatsink Temperature Sensors

The AX2550 includes temperature sensors making contact with the each of the two Heatsink sides of the controller.

These sensors are used to automatically reduce the maximum Amps that the controller can deliver as it overheats. However, the temperature can be read using the RS232 port using the ?m query, or during data logging (see “Analog and R/C Modes Data Logging String Format” on page 166)

The analog value that is reported will range from 0 (warmest) to 255 (coldest). Because of the non-linear characteristics of NTC thermistors, the conversion from measured value to temperature must be done using the correction curve below.

It should be noted that the temperature is measured inside the controller and that it may be temporarily be different than the temperature measured outside the case.

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Temperature Conversion C Source Code

300

250

200

150

100

Reported Analog Value

-40

-30

-20

-10

100

110

120

130

140

150

Temperature in Degrees C

FIGURE 39. Analog reading by controller vs. internal heat sink temperature

Temperature Conversion C Source Code

The code below can be used to convert the analog reading into temperature. It is provided for reference only. Interpolation table is for the internal thermistors.

int ValToHSTemp(int AnaValue) {

// Interpolation table. Analog readings at -40 to 150 oC, in 5o intervals

int TempTable[39] ={248, 246, 243, 240, 235, 230, 224, 217, 208, 199, 188, 177, 165, 153, 140, 128, 116, 104,93, 83, 74, 65, 58, 51, 45, 40, 35, 31, 27, 24, 21, 19, 17, 15, 13, 12, 11, 9, 8};

int LoTemp, HiTemp, lobound, hibound, temp, i;

i=38;

while (TempTable[i] < AnaValue &&i>0)

i--;

if (i < 0)

i=0;

if (i == 38)

return 150; else {

LoTemp =i*5-40;

HiTemp = LoTemp + 5;

lobound = TempTable[i];

hibound = TempTable[i+1];

temp = LoTemp + (5 * ((AnaValue - lobound)*100/ (hibound - lobound)))/100;

return temp; }

}

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Optical Incremental Encoders Overview

SECTION 7 Installing,

Connecting and Using the Encoder Module

This section describes the Encoder input module that is factory installed inside the AX2850 or that may be added onto the AX2550.

Optical Incremental Encoders Overview

Optical incremental encoders are a means for capturing speed and travelled distance on a motor. Unlike absolute encoders which give out a multi-bit number (depending on the resolution), incremental encoders output pulses as they rotate. Counting the pulses tells the application how many revolutions, or fractions of, the motor has turned. Rotation velocity can be determined from the time interval between pulses or by the number of pulses within a given time period. Because they are digital devices, incremental encoders will measure distance and speed with perfect accuracy.

Since motors can move in forward and reverse directions, it is necessary to differentiate the manner that pulses are counted so that they can increment or decrement a position counter in the application. Quadrature encoders have dual channels, A and B, which are electrically phased 90° apart. Thus, direction of rotation can be determined by monitoring the phase relationship between the two channels. In addition, with a dual-channel encoder, a four-time multiplication of resolution can be achieved by counting the rising and falling edges of each channel (A and B). For example, an encoder that produces 250 Pulses per Revolution (PPR) can generate 1,000 Counts per Revolution (CPR) after quadrature.

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Installing, Connecting and Using the Encoder Mod-

A Channel

1 Pulse = 4 Transitions

B Channel

= 4 Counts

Quadrature Signal

FIGURE 40. Quadrature encoder output waveform

The figure below shows the typical construction of a quadrature encoder. As the disk rotates in front of the stationary mask, it shutters light from the LED. The light that passes through the mask is received by the photo detectors. Two photo detectors are placed side by side at so that the light making it through the mask hits one detector after the other to produces the 90o phased pulses.

Count Up

Count Down

LED light source

Rotating

encoder disk

FIGURE 41. Typical quadrature encoder construction

Unlike absolute encoders, incremental encoders have no retention of absolute position upon power loss. When used in positioning applications, the controller must move the motor until a limit switch is reached. This position is then used as the zero reference for all subsequent moves.

Recommended Encoder Types

The module may be used with most incremental encoder module as long as they include the following features:

• Two quadrature outputs (Ch A, Ch B), single ended signal

• 2.5V minimum swing between 0 Level and 1 Level on quadrature output

• 5VDC operation. 100mA or less current consumption per encoder

Stationary mask

Photodetector

More sophisticated incremental encoders with differential outputs, index, and other features may be used, however these additional capabilities will be ignored.

The choice of encoder resolution is very wide and is constrained by the module’s maxi- mum pulse count at the high end and measurement resolution for speed at the low end.

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Installing the Encoder Module

Specifically, the encoder module can process 250,000 counts per seconds. As discussed in the previous section, a count is generated for each transition on the Channel A and Channel B. Therefore the module will work with encoders outputting up to 62,500 pulses per second.

Commercial encoders are rated by their numbers of “Pulses per Revolution” (also sometimes referred as “Cycles per Revolution). Carefully read the manufacturer’s datasheet to understand whether this number represents the number of pulses that are output by each channel during the course of a 360o revolution rather than the total number of transitions on both channels during a 360o revolution. The second number is 4 times larger than the first one.

The formula below gives the pulse frequency at a given RPM and encoder resolution in Pulses per Revolution.

Pulse Frequency in Hz = RPM / 60 * PPR * 4

Example: a motor spinning at 10,000 RPM max, with an encoder with 200 Pulses per Revolution would generate:

10,000 / 60 * 200 * 4 = 133.3 kHz which is well within the 250kHz maximum supported by the encoder module.

An encoder with a 200 Pulses per Revolutions is a good choice for most applications.

A higher resolution will cause the counter to count faster than necessary and possibly reach the encoder module’s maximum frequency limit.

An encoder with a much lower resolution will cause speed to be measured with less precision.

Installing the Encoder Module

The Encoder module is available in kit form for installation by the user inside the AX2550 controller. It may also be ordered factory-installed in the controller by using the product reference AX2850.

FIGURE 42. Encoder Module for AX2550. Factory installed in AX2850

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Installing, Connecting and Using the Encoder Mod-

Follow these simple steps to install:

1- With the power removed, remove the controller’s face plate and slide off the cover.

2- Carefully insert the encoder module on top of the two headers present on the controller’s main board and shown in Figure 43. Beware that the two matting connectors are precisely aligned.

FIGURE 43. Position of Encoder Module on Controller’s main board

3- The encoder module will be held in place by the connectors and the new front bracket’s opening around the RJ11 connector. For added stability, place the foam pad on top of the Encoder module as shown in Figure 44 so that it is held in place by the sliding cover. For use in harsh shock and vibration environments, you may instead solder a metal wire inside the 0.1” hole found on the main board (next to one of the two header) and solder the other en inside the matching hole on the encoder module, as shown on Figure 45.

Cover

Place Foam Block on Encoder module

Encoder Module

Main Board

FIGURE 44. Place foam block between module and cover to hold in place

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Connecting the Encoder

FIGURE 45. Solder wire for robust assembly

4- Slide the cover back on. Install the new face plate.

Connecting the Encoder

The Encoder module uses a widely available 8-pin RJ45 connector identical to those found on all Ethernet devices. The connector provides 5V power to the encoders and has inputs for the two quadrature signals from each encoder. Using multi-level signaling, it is also possible to share the quadrature inputs with limit switches. The figure and table below describe the connector and its pin assignment.

Encoder Module

Solder wire

Main Board

FIGURE 46. Encoder connector

TABLE 14. Encoder Connector Pinout

Cable Color

Pin Name

(when using standard network cable)

1 Encoder 2 - Channel B. Optional Limit Switch 4 Orange/White

2 Encoder 2 - Channel A. Optional Limit Switch 3 Orange

3 Ground (same as pin 7) Green/White

4 5V Out (same as pin 8) Blue

5 Encoder 1 - Channel B. Optional Limit Switch 2 Blue/White

6 Encoder 1 - Channel A. Optional Limit Switch 1 Green

7 Ground (same as pin 3) Brown/White

8 5V Out (same as pin 4) Brown

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Installing, Connecting and Using the Encoder Mod-

Cable Length and Noise Considerations

Cable should not exceed one 3’ (one meter) to avoid electrical noise to be captured by the wiring. A ferrite core filter must be used for length beyond 2’ (60 cm). For longer cable length use an oscilloscope to verify signal integrity on each of the pulse channels and on the power supply.

Ferrite Core

FIGURE 47. Use ferrite core on cable length beyond 2’ or 60cm

Important Warning

Excessive cable length will cause electrical noise to be captured by the controller and cause erratic functioning that may lead to failure. In such situation, stop operation immediately.

Motor - Encoder Polarity Matching

When using the Encoder module for closed loop speed control, it is imperative that when the motor is turning in the forward direction, the counter increments its value and a positive speed value is measured.

Encoder

Using the PC utility, it is possible to exercise the motors and view the encoder readings. See “Encoder Testing and Setting Using the PC Utility” on page 83.

If the Encoder counts backwards when the motor moves forward, correct this by either:

1- Swapping Channel A and Channel B on the encoder connector. This will cause the encoder module to reverse the count direction, or

2- Swapping the leads on the motor. This will cause the motor to rotate in the opposite direction.

Voltage Levels, Thresholds and Limit Switches

The encoder module’s input uses a comparator to reshape the encoder’s output signal. If the signal is below a programmable threshold level, then it is considered to be 0. If above, it is considered to be 1. The output of this comparator feeds the quadrature detector and counters.

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Voltage Levels, Thresholds and Limit Switches

On the 2850 family of controllers, the threshold voltage may be changed under software control to any value between 0 and 5V in order to meet unusual encoder specifications. By default, the threshold level is 2.5V.

Another set of comparators on the same input signals detects pulses that are above and below a fixed 0.5V threshold. Using a special circuitry for creating multi-level signaling (see next section below), the output of these comparators serves to detect the status of optional limit switches.

Figure 49 and Figure 48 show the conditioned signals as seen by the encoder.

In Figure 49, the encoders are connected directly to the Channel A and B inputs. In this case, it will cause a Switch Detection condition because the encoder’s 0 level is below

0.5V, which should be ignored.

Signal on Channel A or B

Quadrature Signal

Switch Detect Signal (Not meaningful)

FIGURE 48. Signals seen by encoder using direct connection and no limit switches

In Figure 48, the encoder and switches are wired to the encoder module using a set of resistors designed to create a multi-level signal combining both pieces of information. Details on the necessary wiring is provided in the next section.

Since the encoder output signal is “shifted-up” by a few volts, it always stays above the Limit Switch comparator’s threshold, and no Switch Detection condition is generated. However, since the limit switches connect to ground when On, the level will dip below the

0.5V and generate a Switch Detection condition.

Signal on Channel A or B

2.5V

0.5V

2.5V

0.5V

Quadrature Signal

Switch Detect Signal

FIGURE 49. Signals seen by encoder using multi-levels and limit switches

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Installing, Connecting and Using the Encoder Mod-

Important Warning

When a limit switch is activated, the encoder signal that is shared with the switch is no longer visible by the encoder module, and pulse counting and speed measurement stops.

Wiring Optional Limit Switches

If limit switches are needed by the application, additional circuitry is required in order to create a multi-level signal that shares the encoder and the switch information. The figure below shows the electrical diagram of the required wiring.

4.7kOhm

5V Out

4.7kOhm

GND

1kOhm

Ch A

Encoder

Ch B

1kOhm

SW1

Ch A In

Ch B In

SW2

GND

FIGURE 50. Signals seen by encoder using multi-levels and limit switches

Using this circuit when the switch is open, a 0V (low-level) output from the encoder goes through a 1k and 4.7k voltage divider, thus creating a voltage that will never be below 0.8V at the encoder module’s input.

When the switch is activated, the module’s input is pulled to 0V.

It is recommended that a voltmeter and/or oscilloscope be used to verify that the right voltage levels are created as the encoder rotates and the switches activate.

Encoder Module

You may also use the Encoder setup/test function in the Roborun utility (see “Encoder Testing and Setting Using the PC Utility” on page 83). If the wiring is correct, the counters should increment/decrement as the motor rotate. The switch indicators should be always off unless the switches are actually activated.

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Wiring Limit Switches Without Encoders

If no encoder is used, the Encoder Module’s inputs can be used to wire limit switches directly with solely a pull-up resistor as shown in the diagram below.

5V Out

4.7kOhm

SW1

4.7kOhm

SW2

4.7kOhm

SW3

4.7kOhm

Ch B In

Ch A In

Ch B In

Ch A In

SW4

FIGURE 51. Signals seen by encoder using multi-levels and limit switches

Effect of Limit Switches

Each pair of limit switches will stop the motion of a given motor in a given direction. This will have the effect of stopping the motor when a limit is reached while allowing motion in the other direction, away for that limit.

GND

8 - 4

Encoder Input

7 - 3

TABLE 15. Effects of Limit Switches 1 and 2 on Motor 1

SW1 SW2 Motor 1 Fwd Motor 1 Rev

OFF OFF Allowed Allowed

ON OFF Stopped Allowed

OFF ON Allowed Stopped

ON ON Stopped Stopped

TABLE 16. Effects of Limit Switches 3 and 4 on Motor 2

SW3 SW4 Motor 2 Fwd Motor 2 Rev

OFF OFF Allowed Allowed

ON OFF Stopped Allowed

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Installing, Connecting and Using the Encoder Mod-

TABLE 16. Effects of Limit Switches 3 and 4 on Motor 2

SW3 SW4 Motor 2 Fwd Motor 2 Rev

OFF ON Allowed Stopped

ON ON Stopped Stopped

In Single Channel Mode, limit switches 3 and 4 are used. This is to allow direct connection of an encoder on the inputs for channel 1 and direct connection of switches on the inputs

for channel 2

TABLE 17. Effects of Limit Switches 3 and 4 on Motor 2 in Single Channel Configuration

SW3 SW4 Motor Fwd Motor Rev

OFF OFF Allowed Allowed

ON OFF Stopped Allowed

OFF ON Allowed Stopped

ON ON Stopped Stopped

Using the Encoder Module to Measure Distance

As the encoders rotate, their quadrature outputs is automatically processed and increments/decrements two 32-bit counter inside the Encoder Module. There is one 32-bit counter for each of the encoders.

The counter values are stored as a signed binary numbers, ranging from -2,147,836,648 to +2,147,836,647 (Hexadecimal format of value 80000000 to 7FFFFFFF respectively. When the maximum or minimum counter values are reached, the counters automatically roll over to zero.

The counters can be read and set using the commands described in “The Encoder Module contains its own Microcontroller and firmware in Flash. When present, it responds to a large set of dedicated commands and queries via the controller’s serial port. See “RS232 Encoder Command Set” on page 155.” on page 82.

Using the Encoder to Measure Speed

The encoder module will automatically compute rotation speed for each encoder. The resulting measured speed is a value ranging from 0 to + 127 and 0 to -127, where 127 represent a relative ratio of a maximum speed value chosen by the user.

For example, if the encoder module is configured so that the highest measured speed value is 3,000 RPM, then a reading of 63 (127/2) would be 1,500 RPM.

The relationship between the measured speed and the actual speed is a factor of two variable parameters: a Time Based period value stored inside the Encoder module and the Encoder’s number of Pulses per Revolution. Note: the Encoder’s number of Pulses per Revolution is not stored in the controller.

The Time Base is a number of 256us time intervals between two counter reads.

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Using the Encoder to Track Position

A simple procedure is included in the Roborun PC utility to easily determine and set these parameters.

For information, the exact formula is shown below:

Measured Speed Value = RPM * PPR * 4 * (Time Base+1) * 256 / (60 * 1000000)

or Measured Speed Value = RPM * PPR * (Time Base + 1) / 58593.75

Example: a motor spinning at 1,000 RPM, with an encoder with 200 Pulses per Revolution, and a Time Base set at 4 will produce the following measurement:

1000 *200 * (4 + 1) / 58593.75 = 17

The same formula modified to show the actual RPM at a given Measure Speed Value is as follows:

RPM = Measured Speed Value * 60 * 1000000 / (PPR * 4 * 256 * (Time Base+1))

or RPM = Measured Speed Value * 58593.75 /((Time Base + 1) * PPR)

In our example, a measured speed value of 127 corresponds to the following measurable max actual RPM values.

RPM at Max Measurable Speed Value = 127 * 58593.75 / ((4 + 1) * 200) = 7441 RPM

A measured speed value of 1 corresponds to the following measurable min. actual RPM values.

RPM at Min. Measurable Speed Value = 1 * 58593.75 / ((4 + 1) * 200) = 58.6 RPM

The Roborun Utility automatically makes the above calculations when setting up the encoder.

Important Notice

The time base value should not exceed 63 so that a new speed value can be measured at every 16ms loop. The roborun utility automatically limits the time base value that can be entered.

Using the Encoder to Track Position

The encoder module can be used to report the distance between the actual motor position and a desired destination. The resulting measured “distance” can then be used by the con- troller in the position mode to move the motor in the right direction until the destination is reached. This movement is controlled by the PID position algorithm inside the controller and is therefore best suited at tracking position.

Since the controller uses a signed 8-bit value (-127 to +127) for the distance measurement in the Position Mode, a special algorithm is used to convert the real distance which can be much higher than -127 to +127, as both the counter and destination registers are 32-bit wide.

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Installing, Connecting and Using the Encoder Mod-

The actual formula is as follows:

Distance = (Destination - Counter value) / Divider

Where: divider is a configurable parameter of value 1, 2, 4, 8, 16, 32, 64 or 127

If computed distance is less than -127, then reported distance is -127

If computed distance is larger than +127, then reported distance is +127

Counter= 50,000

FIGURE 52. Small distance computation example

Destination= 50,050

distance at divider 50 1 25 2 12 4 6 8 3 16 1 32 0 64 0 128

Destination= 50,000

Counter= 45,000

distance at divider 127 1 127 2 127 4 127 8 127 16 127 32 78 64 39 128

FIGURE 53. Large distance computation example

Important Notice

Encoders do not report an absolute position value but a count that is relative to the point where the motor shaft was at power up. It is typically necessary to have the motors moved to a “home” position and reset the counters at that reference point.

RS232 Communication with the Encoder Module

The Encoder Module contains its own Microcontroller and firmware in Flash. When present, it responds to a large set of dedicated commands and queries via the controller’s serial port. See “RS232 Encoder Command Set” on page 155.

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Encoder Testing and Setting Using the PC Utility

Extensive diagnostic, calibration, setting and testing support is provided in the Roborun PC utility. Basic instructions on how to install and run the PC utility can be found in “Encoder Setting and Testing” on page 184.

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Installing, Connecting and Using the Encoder Mod-

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Mode Description

SECTION 8 Closed Loop

Position Mode

This section describes the AX2550 Position mode, how to wire the motor and position sensor assembly and how to tune and operate the controller in this mode.

Mode Description

In this mode, the axle of a geared-down motor is coupled to a position sensor that is used to compare the angular position of the axle versus a desired position. The controller will move the motor so that it reaches this position.

This unique feature makes it possible to build ultra-high torque “jumbo servos” that can be used to drive steering columns, robotic arms, life-size models and other heavy loads.

The AX2550 incorporates a full-featured Proportional, Integral, Differential (PID) control algorithm for quick and stable positioning.

Selecting the Position Mode

The position mode is selected by changing the Motor Control parameter in the controller to either

• A Open Loop Speed, B Position

• A Closed Loop Speed, B Position

• A and B Position

Note that in the first two modes, only the second motor will operate in the Position mode.

Changing the parameter is best done using the Roborun Utility. See “Loading, Changing Controller Parameters” on page 181.

For safety reasons and to prevent this mode from being accidentally selected, Position modes CANNOT be selected by configuring the controller using the built-in switches and display.

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Closed Loop Position Mode

Position Sensor Selection

The AX2550 may be used with the following kind of sensors:

• Potentiometers

• Hall effect angular sensors

• Optical Encoders (with Encoder Module)

The first two are used to generate an analog voltage ranging from 0V to 5V depending on their position. They will report an absolute position information at all times.

Optical encoders report incremental changes from a reference which is their initial position when the controller is powered up or reset. Using Optical Encoders in this mode is possible but requires special handling that is described in Figure , “Using the Encoder to Track Pos i tion,” on page 81.

Sensor Mounting

Proper mounting of the sensor is critical for an effective and accurate position mode operation. Figure 54 shows a typical motor, gear box, and sensor assembly.

Position Sensor

Gear box

FIGURE 54. Typical motor/potentiometer assembly in Position Mode

The sensor is composed of two parts:

• a body which must be physically attached to a non-moving part of the motor assem-

bly or the robot chassis, and

• an axle which must be physically connected to the rotating part of the motor you

wish to position.

A gear box is necessary to greatly increase the torque of the assembly. It is also necessary to slow down the motion so that the controller has the time to perform the position control algorithm. If the gearing ratio is too high, however, the positioning mode will be very sluggish.

Position Feedback

A good ratio should be such that the output shaft rotates at 1 to 10 rotations per second (60 to 600 RPM) when the motor is at full speed.

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Feedback Potentiometer wiring

The mechanical coupling between the motor and the sensor must be as tight as possible. If the gear box is loose, the positioning will not be accurate and will be unstable, potentially causing the motor to oscillate.

Some sensor, such as potentiometers, have a limited rotation range of typically 270 degrees (3/4 of a turn), which will in turn limit the mechanical motion of the motor/potentiometer assembly. Consider using a multi-turn potentiometer as long as it is mounted in a manner that will allow it to turn throughout much of its range, when the mechanical assembly travels from the minimum to maximum position.

Important Notice:

Potentiometers are mechanical devices subject to wear. Use better quality potentiometers and make sure that they are protected from the elements. Consider using a solid state hall position sensor in the most critical applications. Optical encoders may also be used when operated as discussed in “Using the Encoder to Measure Speed” on page 80.

Feedback Potentiometer wiring

When using a potentiometer, it must be wired so that it creates a voltage that is proportional to its angular position: 0V at one extreme, +5V at the other. A 10K potentiometer value is recommended for this use.

Analog Feedback is normally connected to the Analog Inputs 1 and 2, except when the controller is configured in Analog Mode. In Analog mode, Analog Inputs 1 and 2 are already used to supply the command. Therefore Analog inputs 3 and 4 are used for feedback

Feedback Potentiometer wiring in RC or RS232 Mode

In RC or RS232 mode, feedback is connected to Analog Inputs 1 and 2. Connecting the potentiometer to the controller is as simple as shown in the diagram on below.

Note that this wiring must not be used if the controller is configured in Analog mode but is switched in RS232 after power up using the method discussed in “Entering RS232 from R/ C or Analog mode” on page 136. Instead, used the wiring for Analog mode discussed in the next section.

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Closed Loop Position Mode

2k - 10k 2k - 10k

14 +5V

5 Ground

Feedback 1

Feedback 2

FIGURE 55. Pot wiring for RS232 or RC Command and Analog Feedback

Feedback Potentiometer wiring in Analog Mode

When the controller is configured in Analog mode, the analog inputs 1 and 2 are used for commands while the analog inputs 3 and 4 are used for feedback. Analog inputs 3 and 4 have different characteristics than inputs 1 and 2, and so require a lower resistance potentiometer in order to guarantee accuracy

Note that the analog inputs 3 and 4 are only available on the AX2550 with PCB revision 6.1 or above. The PCB revision can be found on the sticker affixed at the bottom of the case. Roborun will detect the new hardware revision and display Rev B on the screen.

2k 2k 2k - 10k 2k - 10k

11 Ana1

10 Ana2

12 Ana3*

8 Ana4*

14 +5V

5 Ground

FIGURE 56. Pot wiring for Analog Command and Analog Feedback

Analog inputs 3 and 4 have different characteristics than inputs 1 and 2, and so require a lower resistance potentiometer in order to guarantee accuracy.

Important Notice

This wiring is also the one to use when the controller is in Analog mode but switched to RS232 after reset using the method discussed in “Entering RS232 from R/C or Analog mode” on page 136

Command 1

Command 2

Feedback 1

Feedback 2

11 Ana1

10 Ana2

12 Ana3*

8 Ana4*

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Analog Feedback on Single Channel Controllers

On Single Channel controllers (SC Version - not to be confused with Dual Channel controllers of which only one channel is used for position control - See “Single Channel Operation” on page 177.), the controller accepts one command and uses one input for feedback.

Feedback Wiring in RC or RS232 Mode on Single Channel Controllers

When the controller is configured for RS232 or RC command, the wiring of the feedback must be done as shown in the figure below.

14 +5V

2k - 10k

Feedback

5 Ground

11 Ana1

10 Ana2

12 Ana3*

8 Ana4*

FIGURE 57. Pot wiring on Single Channel controllers (SCversion) and Analog Command

Feedback Wiring in Analog Mode on Single Channel Controllers

When the controller is configured in Analog mode, the analog input 1 is used for commands while the analog input 4 is used for feedback. Note that the analog inputs 3 and 4 are only available on the AX2550 with PCB revision 6.1 or above. The PCB revision can be found on the sticker affixed at the bottom of the case. Roborun will detect the new hardware revision and display Rev B on the screen.

14 +5V

2k 2k - 10k

Command

Feedback

FIGURE 58. Pot wiring on Single Channel controllers (SC version) and Analog Command

5 Ground

11 Ana1

10 Ana2

12 Ana3*

8 Ana4*

Analog inputs 3 and 4 have different characteristics than inputs 1 and 2, and so require a lower resistance potentiometer in order to guarantee accuracy.

Important Notice

AX2550 Motor Controller User’s Manual 89

Closed Loop Position Mode

This wiring is also the one to use when the controller is in Analog mode but switched to RS232 after reset using the method discussed in “Entering RS232 from R/C or Analog mode” on page 136

Using Optical Encoders in Position Mode

The AX2550 and AX1500 may be equipped with an optional Optical Encoder Module. Optical Encoders require special handling. See Figure 7, “Installing, Connecting and Using the Encoder Module,” on page 71 for a detailed discussion.

Sensor and Motor Polarity

The sensor polarity (i.e. which rotation end produces 0 or 5V) is related to the motor’s polarity (i.e. which direction the motor turns when power is applied to it).

In the Position mode, the controller compares the actual position, as measured by the sensor, to the desired position. If the motor is not at that position, the controller will apply power to the motor so that it turns towards that destination until reached.

Important Warning:

If there is a polarity mismatch, the motor will turn in the wrong direction and the position will never be reached. The motor will turn continuously with no way of stopping it other than cutting the power or hitting the Emergency Stop button.

Determining the right polarity is best done experimentally using the Roborun utility (see “Using the Roborun Configuration Utility” on page 177) and following these steps:

1. Disconnect the controller’s Motor Power (thick power wires).

2. Configure the controller in Position Mode using the PC utility.

3. Loosen the sensor’s axle from the motor assembly.

4. Launch the Roborun utility and click on the Run tab. Click the “Start” button to

begin communication with the controller. The sensor values will be displayed in the Ana1 and Ana2 boxes.

5. Move the sensor manually to the middle position until a value of “0” is measured

using Roborun utility

6. Verify that the motor sliders are in the “0” (Stop) position. Since the desired posi-

tion is 0 and the measured position is 0, the controller will not attempt to move the motors. The Power graph on the PC must be 0.

7. Apply power to the Motor Power input (thick power wires). The motor will be

stopped.

8. With a hand ready to disconnect the Motor Power cable or ready to press the “Pro-

gram” and “Set” buttons at the same time (Emergency Stop), SLOWLY move the sensor off the center position and observe the motor’s direction of rotation.

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Encoder Error Detection and Protection

9. If the motor turns in the direction in which the sensor was moved, the polarity is

correct. The sensor axle may be tighten to the motor assembly.

10. If the motor turns in the direction away from the sensor, then the polarity is

reversed. The wire polarity on the motors should be exchanged. If using a potentiometer as sensor, the GND and +5V wires on the potentiometer may be swapped instead. If using an Optical Encoder, ChA and ChB outputs can be swapped.

11. Move the sensor back to the center point to stop the motor. Cut the power if con-

trol is lost.

12. If the polarity was wrong, invert it and repeat steps 8 to 11.

13. Tighten the sensor.

Important Safety Warning

Never apply a command that is lower than the sensor’s minimum output value or higher than the sensor’s maximum output value as the motor would turn forever try- ing to reach a position it cannot. For example, if the max position of a potentiometer is 4.5V, which is a position value of 114, a destination command of 115 cannot be reached and the motor will not stop.

Encoder Error Detection and Protection

The AX2550 contains an Encoder detection and protection mechanism that will cause the controller to halt if no motion is detected on either Encoder while a power level of 25% or higher is applied to the motor. If such an error occurs, the controller will halt permanently until its power is cycled or it is reset. An Encoder error is one of the conditions that is signaled by the LED rapidly flashing an “8” character (see “Permanent Faults” on page 106).

Adding Safety Limit Switches

The Position mode depends on the position sensor providing accurate position information. If the potentiometer is damaged or one of its wire is cut, the motors may spin continuously in an attempt to reach a fictitious position. In many applications, this may lead to serious mechanical damage.

To limit the risk of such breakage, it is recommended to add limit switches that will cause the motors to stop if unsafe positions have been reached independent of the potentiometer reading.

If the controller is equipped with and Encoder module, the simplest solution is to implement limit switches as shown in “Wiring Optional Limit Switches” on page 78. This wiring can be used whether or not Encoders are used for feedback.

If no Encoder module is present, an alternate method is shown in Figure 59. This circuit uses Normally Closed limit switches in series on each of the motor terminals. As the motor reaches one of the switches, the lever is pressed, cutting the power to the motor. The diode in parallel with the switch allows the current to flow in the reverse position so that the motor may be restarted and moved away from that limit.

AX2550 Motor Controller User’s Manual 91

Closed Loop Position Mode

The diode polarity depends on the particular wiring and motor orientation used in the application. If the diode is mounted backwards, the motor will not stop once the limit switch lever is pressed. If this is the case, reverse the diode polarity.

The diodes may be eliminated, but then it will not be possible for the controller to move the motor once either of the limit switches has been triggered.

The main benefit of this technique is its total independence on the controller’s electronics and its ability to work in practically all circumstances. Its main limitation is that the switch and diode must be capable of handling the current that flows through the motor. Note that the current will flow though the diode only for the short time needed for the motor to move away from the limit switches.

SW1 SW2

Motor

Controller

FIGURE 59. Safety limit switches interrupting power to motors

Another method uses the AX2550’s Emergency Stop input to shut down the controller if any of the limit switches is tripped. Figure 60 shows the wiring diagram used in this case. Each of the limit switches is a Normally Open switch. Two of these switches are typically required for each motor. Additional switches may be added as needed for the second motor and/or for a manual Emergency Stop. Since very low current flows through the switches, these can be small, low cost switches.

The principal restriction of this technique is that it depends on the controller to be fully functioning, and that once a switch is activated, the controller will remain inactive until the switch is released. In most situations, this will require manual intervention. Another limitation is that both channels will be disabled even if only one channel caused the fault.

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Using Current Limiting as Protection

Manual Emergency Stop Switch

FIGURE 60. Safety limit using AX2550’s Emergency Stop input

SW1

Important Warning

Limit switches must be used when operating the controller in Position Mode. This will significantly reduce the risk of mechanical damage and/or injury in case of damage to the position sensor or sensor wiring.

Using Current Limiting as Protection

It is a good idea to set the controller’s current limit to a low value in order to avoid high cur- rent draws and consequential damage in case the motor does not stop where expected. Use a value that is no more than 2 times the motor’s draw under normal load conditions.

Motor

Controller

SW2

Emergency Stop InputGround

Control Loop Description

The AX2550 performs the Position mode using a full featured Proportional, Integral and Differential (PID) algorithm. This technique has a long history of usage in control systems and works on performing adjustments to the Power Output based on the difference measured between the desired position (set by the user) and the actual position (captured by the position sensor).

Figure 61 shows a representation of the PID algorithm. Every 16 milliseconds, the controller measures the actual motor position and substracts it from the desired position to compute the position error.

The resulting error value is then multiplied by a user selectable Proportional Gain. The resulting value becomes one of the components used to command the motor. The effect of this part of the algorithm is to apply power to the motor that is proportional with the distance between the current and desired positions: when far apart, high power is applied, with the power being gradually reduced and stopped as the motor moves to the final position. The Proportional feedback is the most important component of the PID in Position mode.

AX2550 Motor Controller User’s Manual 93

Closed Loop Position Mode

A higher Proportional Gain will cause the algorithm to apply a higher level of power for a given measured error, thus making the motor move quicker. Because of inertia, however, a faster moving motor will have more difficulty stopping when it reaches its desired position. It will therefore overshoot and possibly oscillate around that end position.

Analog Position Sensor

or Optical Encoder

Desired Position

A/D

Measured Position

Proportional Gain

E= Error

Integral Gain

dE dt

Output

FIGURE 61. PID algorithm used in Position mode

The Differential component of the algorithm computes the changes to the error from one 16 ms time period to the next. This change will be a relatively large number every time an abrupt change occurs on the desired position value or the measured position value. The value of that change is then multiplied by a user-selectable Differential Gain and added to the output. The effect of this part of the algorithm is to give a boost of extra power when starting the motor due to changes to the desired position value. The differential component will also help dampen any overshoot and oscillation.

The Integral component of the algorithm performs a sum of the error over time. In the position mode, this component helps the controller reach and maintain the exact desired position when the error would otherwise be too small to energize the motor using the Proportional component alone. Only a very small amount of Integral Gain is typically required in this mode.

PID tuning in Position Mode

As discussed above, three parameters - Proportional Gain, Integral Gain and Differential Gain - can be adjusted to tune the position control algorithm. The ultimate goal in a well tuned PID is a motor that reaches the desired position quickly without overshoot or oscillation.

Differential Gain

Because many mechanical parameters such as motor power, gear ratio, load and inertia are difficult to model, tuning the PID is essentially a manual process that takes experimentation.

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PID tuning in Position Mode

The Roborun PC utility makes this experimentation easy by providing one screen for changing the Proportional, Integral and Differential gains and another screen for running and monitoring the motors.

When tuning the motor, first start with the Integral Gain at zero, increasing the Proportional Gain until the motor overshoots and oscillates. Then add Differential gain until there is no more overshoot. If the overshoot persists, reduce the Proportional Gain. Add a minimal amount of Integral Gain. Further fine tune the PID by varying the gains from these positions.

To set the Proportional Gain, which is the most important parameter, use the Roborun utility to observe the three following values:

• Command Value

• Actual Position

• Applied Power

With the Integral Gain set to 0, the Applied Power should be:

Applied Power = (Command Value - Actual Position) * Proportional Gain

Experiment first with the motor electrically or mechanically disconnected and verify that the controller is measuring the correct position and is applying the expected amount of power to the motor depending on the command given.

Verify that when the Command Value equals the Actual Position, the Applied Power equals to zero. Note that the Applied Power value is shown without the sign in the PC utility.

In the case where the load moved by the motor is not fixed, the PID must be tuned with the minimum expected load and tuned again with the maximum expected load. Then try to find values that will work in both conditions. If the disparity between minimal and maximal possible loads is large, it may not be possible to find satisfactory tuning values.

Note that the AX2550 uses one set of Proportional, Integral and Differential Gains for both motors, and therefore assumes that similar motors, mechanical assemblies and loads are present at each channel.

AX2550 Motor Controller User’s Manual 95

Closed Loop Position Mode

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Mode Description

SECTION 9 Closed Loop

Speed Mode

This section discusses the AX2550 Close Loop Speed mode.

Mode Description

In this mode, an analog or digital speed sensor measures the actual motor speed and compares it to the desired speed. If the speed changes because of changes in load, the controller automatically compensates the power output. This mode is preferred in precision motor control and autonomous robotic applications.

The AX2550 incorporates a full-featured Proportional, Integral, Differential (PID) control algorithm for quick and stable speed control.

Selecting the Speed Mode

The speed mode is selected by changing the Motor Control parameter in the controller to either:

• A and B Closed Loop Speed, Separate

• A and B Closed Loop Speed, Mixed

• A Closed Loop Speed, B Position

Note that in the last selection, only the first motor will operate in the Closed Loop Speed mode.

Changing the parameter to select this mode is done using the Roborun Utility. See “Load- ing, Changing Controller Parameters” on page 181.

For safety reasons and to prevent this mode from being accidentally selected, Closed Loop Speed modes CANNOT be selected by configuring the controller using the built-in switches and display.

AX2550 Motor Controller User’s Manual 97

Closed Loop Speed Mode

Using Optical Encoder for Speed Feedback (AX2850 only)

Digital Optical Encoders may be used to capture accurate motor speed. This capability is only available on controllers fitted with the optional encoder module.

Detailed information on how to install and wire optical encoders is provided at “Installing, Connecting and Using the Encoder Module” on page 71.

If using optical encoders, omit the Analog Tachometer discussion in this section and resume reading from “Control Loop Description” on page 100. Optical Encoders require special handling. See “Installing, Connecting and Using the Encoder Module” on page 71 for a detailed discussion.

Tachometer or Encoder Mounting

Proper mounting of the speed sensor is critical for an effective and accurate speed mode operation. Figure 62 shows a typical motor and tachometer or encoder assembly.

Analog Tachometer or Optical Encoder

Speed feedbackSpeed feedback

FIGURE 62. Motor and speed sensor assembly needed for Close Loop Speed mode

Tachometer wiring

The tachometer must be wired so that it creates a voltage at the controller’s analog input that is proportional to rotation speed: 0V at full reverse, +5V at full forward, and 0 when stopped.

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Speed Sensor and Motor Polarity

Connecting the tachometer to the controller is as simple as shown in the diagram below.

1kOhm

Zero Adjust 100 Ohm pot

1kOhm

Max Speed Adjust 10kOhm pot

Ta c h

FIGURE 63. Tachometer wiring diagram

Speed Sensor and Motor Polarity

The tachometer or encoder polarity (i.e. which rotation direction produces a positive of negative speed information) is related to the motor’s rotation speed and the direction the motor turns when power is applied to it.

+5V 14

Ana 1: 11 Ana 2: 10 Ana 3: 12 Ana 4: 8

Ground 5

Internal Resistors and Converter

47kOhm

A/D

10kOhm

47kOhm

In the Closed Loop Speed mode, the controller compares the actual speed, as measured by the tachometer, to the desired speed. If the motor is not at the desired speed and direction, the controller will apply power to the motor so that it turns faster or slower, until reached.

Important Warning:

If there is a polarity mismatch, the motor will turn in the wrong direction and the speed will never be reached. The motor will turn continuously at full speed with no way of stopping it other than cutting the power or hitting the Emergency Stop buttons.

Determining the right polarity is best done experimentally using the Roborun utility (see “Using the Roborun Configuration Utility” on page 177) and following these steps:

1. Disconnect the controller’s Motor Power.

2. Configure the controller in Open Loop Mode using the PC utility. This will cause the

motors to run in Open Loop for now.

3. Launch the Roborun utility and click on the Run tab. Click the “Start” button to

begin communication with the controller. The tachometer values will be displayed in the appropriate Analog input value boxe(s) which will be labeled Ana 1 and Ana 2. If encoders are used, look for the reported speed value in the Enc boxes.

4. Verify that the motor sliders are in the “0” (Stop) position.

5. If a tachometer is used, verify that the measured speed value read is 0 when the

motors are stopped. If not, trim the “0” offset potentiometer.

6. Apply power to the Motor Power wires. The motor will be stopped.

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Closed Loop Speed Mode

7. Move the cursor of the desired motor to the right so that the motor starts rotating,

and verify that a positive speed is reported. Move the cursor to the left and verify that a negative speed is reported.

8. If the tachometer or encoder polarity is the same as the applied command, the wir-

ing is correct.

9. If the tachometer polarity is opposite of the command polarity, then either reverse

the motor’s wiring, or reverse the tachometer wires. If an encoder is used, swap its CHA and ChB outputs

10. If a tachometer is used, proceed to calibrate the Max Closed Loop speed.

11. Set the controller parameter to the desired Closed Loop Speed mode using the

Roborun utility.

Adjust Offset and Max Speed

For proper operation, the controller must see a 0 analog speed value (2.5V voltage on the analog input).

To adjust the 0 value when the motors are stopped, use the Roborun utility to view the analog input value while the tachometer is not turning. Move the 0 offset potentiometer until a stable 0 is read. This should be right around the potentiometer’s middle position.

The tachometer must also be calibrated so that it reports a +127 or -127 analog speed value (5V or 0V on the analog input, respectively) when the motors are running at the maximum desired speed in either direction. Since most tachometers will generate more than +/- 2.5V, a 10kOhm potentiometer must be used to scale its output.

To set the potentiometer, use the Roborun utility to run the motors at the desired maximum speed while in Open Loop mode (no speed feedback). While the tachometer is spinning, adjust the potentiometer until the analog speed value read is reaching 126.

Note: The maximum desired speed should be lower than the maximum speed that the motors can spin at maximum power and no load. This will ensure that the controller will be able to eventually reach the desired speed under most load conditions.

Important Warning:

It is critically important that the tachometer and its wiring be extremely robust. If the tachometer reports an erroneous voltage or no voltage at all, the controller will consider that the motor has not reached the desired speed value and will gradually increase the applied power to the motor to 100% with no way of stopping it until power is cut off or the Emergency Stop is activated.

Control Loop Description

The AX2550 performs the Closed Loop Speed mode using a full featured Proportional, Integral and Differential (PID) algorithm. This technique has a long history of usage in control systems and works on performing adjustments to the Power Output based on the differ-

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RoboteQ AX2850 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Revision History

Read this Section First

This product is intended for use with rechargeable batteries

Do not Connect to a RC Radio with a Battery Attached

Beware of Motor Runaway in Improperly Closed Loop

What you will need

Locating the Switches, Wires and Connectors

Connecting to the Batteries and Motors

Important Warning

Important Warning

Connecting to the 15-pin Connector

Connecting the R/C Radio

Important Warning

Powering On the Controller

Button Operation

Default Controller Configuration

Connecting the controller to your PC using Roborun

Obtaining the Controller’s Software Revision Number

Exploring further

Product Description

Technical features

Power Connections

Important Warning

Controller Power

Controller Powering Schemes

Powering the Controller from a single Battery

Important Warning

Important Warning

Important Warning

Powering the Controller Using a Main and Backup Battery

Important Warning

Connecting the Motors

Important Warning

Single Channel Operation

Converting the AX2550 to Single Channel

Power Fuses

Important Warning

Wire Length Limits

Important Warning

Electrical Noise Reduction Techniques

Power Regeneration Considerations

Important Warning

Important Warning

Overvoltage Protection

Undervoltage Protection

Using the Controller with a Power Supply

Basic Operation

Input Command Modes

Selecting the Motor Control Modes

Open Loop, Separate Speed Control

Open Loop, Mixed Speed Control

Closed Loop Speed Control

Close Loop Position Control

User Selected Current Limit Settings

Temperature-Based Current Limitation

Battery Current vs. Motor Current

Important Warning

Regeneration Current Limiting

Programmable Acceleration

Important Warning

Command Control Curves

Left / Right Tuning Adjustment

Activating Brake Release or Separate Motor Excitation

Emergency Shut Down Using Controller Switches

Emergency Stop using External Switch

Inverted Operation

Special Use of Accessory Digital Inputs

Using the Inputs to Activate the Buffered Output

Using the Inputs to turn Off/On the Power MOSFET transistors

Self-Test Mode

Important Warning

AX2550 Connections

AX2550’s Inputs and Outputs

I/O List and Pin Assignment

Connecting devices to Output C

Important warning: