RP6 ROBOT BASE
RP6-BASE
RP6v2-BASE
©2007 - 2012 AREXX Engineering
www.arexx.com
RP6
Robot System
Manual
- English -
Version RP6-BASE-EN-20120115
for RP6 and RP6v2
IMPORTANT INFORMATION!
Please read carefully!
Before you start operating the RP6, RP6v2 or any of the additional
equipment, you must read this manual and the manuals for add-on
modules completely! The documentation contains information about
how to operate the systems properly and how to avoid dangerous situations! Furthermore the manuals provide important details, which may
be unknown to average users.
Paying no attention to this manual will cause a loss of warranty! Additionally, AREXX Engineering cannot be made responsible for any damages caused by neglecting the manual's instructions!
Please pay special attention to the chapter “Safety instructions”!
Do not connect the USB Interface to your PC before you
have read chapter 3 – “Hardware and Software Setup”
and completed the software installation!
Legal Notice
©2007 - 2012 AREXX Engineering
Nervistraat 16
8013 RS Zwolle
The Netherlands
Tel.: +31 (0) 38 454 2028
Fax.: +31 (0) 38 452 4482
"RP6 Robot System" is a trademark of
AREXX Engineering.
All other trademarks used in this document
belong to their owners.
This manual is protected by copyright. No
part of it may be copied, reproduced or distributed without the prior written permission
of the editor!
Changes in product specifications and scope
of delivery are reserved. The contents of
this manual may change at any time without
prior notice.
New versions of this manual will be published on our website:
http://www.arexx.com/
Although we carefully control contents, we do not assume any liability for the contents of
external websites referred to in this manual. Solely the operators of these pages bear responsibility for the contents.
Limitations in Warranty and Liability
The warranty of AREXX Engineering is limited exclusively to the exchange of devices within
legal warranty periods in case of hardware defects, such as mechanical damage, missing or
wrong assembly of electronic components, excluding socketed circuits. To the extent permitted by applicable law, AREXX Engineering assumes no liability for any damage resulting
directly or indirectly from the use of the device.
Irreversible modifications (e.g. soldering additional components, drilling holes, etc.) or
damaging the devices by neglecting the instructions in this manual will void warranty.
No warranties can be given with respect to individual requirements to the included software, nor to the error-free and uninterrupted operation of the software.
Additionally, the software may be modified and loaded onto the system by the user. Therefore the user is responsible for software quality and the overall system performance of the
robot.
AREXX Engineering guarantees the functionality of supplied example software as long as
the specified operating conditions are respected. If the devices are operated beyond these
conditions and the device or the PC-software is malfunctioning or gets defective, the customer will be charged for all service costs, repairs and corrections. Please also pay attention to the corresponding license agreements on the CD-ROM!
Symbols
The following Symbols are used in this manual:
The “Attention!” Symbol is used to mark important details.
Neglecting these instructions may damage or destroy the robot and/or additional components and you may risk your own
or others health!
The "Information" Symbol is used to mark useful tips and
tricks or background information. In this case the information
is to be considered as “useful, but not necessary”.
Contents
1. Introduction ................................................................................. 6
1.1. Technical support .................................................................... 7
1.2. Scope of delivery – RP6 ........................................................... 7
1.3. Scope of delivery - RP6v2 ........................................................ 8
1.4. The RP6v2 and Expansion possibilities ....................................... 8
1.5. Features and technical Data .................................................... 11
1.6. What can the RP6 do? ............................................................ 14
1.7. Application proposals and ideas ............................................... 15
2. The RP6 in detail ......................................................................... 16
2.1. Control System ..................................................................... 17
2.1.1. Bootloader.......................................................................19
2.2. Power Supply ........................................................................ 19
2.3. Sensors ............................................................................... 20
2.3.1. Battery Voltage Sensor......................................................20
2.3.2. Light Sensors (LDRs).........................................................20
2.3.3. Anti Collision System (ACS)................................................21
2.3.4. Bumpers..........................................................................22
2.3.5. Motor Current Sensors.......................................................22
2.3.6. Encoders.........................................................................23
2.4. Drive System ........................................................................ 24
2.5. Expansion System ................................................................. 25
2.5.1. The I²C Bus.....................................................................26
2.5.2. Expansion Connectors.......................................................27
3. Hardware and Software Setup ....................................................... 29
3.1. Safety Instructions ................................................................ 29
3.1.1. Electrostatic Discharges and Shorts.....................................29
3.1.2. Environment of the Robot..................................................30
3.1.3. Supply Voltage.................................................................30
3.2. Software Setup ..................................................................... 31
3.2.1. The RP6 CD-ROM..............................................................31
3.2.2. WinAVR - for Windows.......................................................32
3.2.3. AVR-GCC, avr-libc and avr-binutils - for Linux ......................32
3.2.3.1. Automatic install script ...............................................34
3.2.3.2. Manual install procedure .............................................35
3.2.3.3. Setting the path ........................................................36
3.2.4. Java 6 ............................................................................37
3.2.4.1. Windows ..................................................................37
3.2.4.2. Linux .......................................................................37
3.2.5. RobotLoader.....................................................................38
3.2.6. RP6 Library, RP6 CONTROL Library and Example programs.....38
3.3. Connecting the USB Interface – Windows ................................. 39
3.3.1. Check if the device is properly connected.............................39
3.3.2. Driver uninstall.................................................................40
3.4. Connecting the USB Interface – Linux ...................................... 40
3.5. Finalizing Software installation ................................................ 40
3.6. Inserting Batteries ................................................................. 41
3.7. Charging the Batteries ........................................................... 43
3.8. The first test ......................................................................... 43
3.8.1. Connecting the USB Interface and start RobotLoader.............44
4. Programming the RP6 .................................................................. 53
4.1. Configuring the source code Editor .......................................... 53
4.1.1. Creating menu entries.......................................................53
4.1.2. Configure Syntax Highlighting.............................................56
4.1.3. Opening and compiling sample projects...............................58
4.2. Program upload to the RP6 ..................................................... 60
4.3. Why C? And what's “GCC”? .................................................... 61
4.4. C – Crash Course for beginners ............................................... 62
4.4.1. Literature.........................................................................62
4.4.2. First program...................................................................63
4.4.3. C basics...........................................................................65
4.4.4. Variables.........................................................................66
4.4.5. Conditional statements......................................................68
4.4.6. Switch-Case.....................................................................70
4.4.7. Loops..............................................................................71
4.4.8. Functions.........................................................................72
4.4.9. Arrays, Strings, Pointers....................................................75
4.4.10. Program flow and interrupts.............................................76
4.4.11. The C-Preprocessor.........................................................77
4.5. Makefiles .............................................................................. 78
4.6. The RP6 function library (RP6Library) ....................................... 79
4.6.1. Initializing the microcontroller.............................................79
4.6.2. UART Functions (serial interface)........................................80
4.6.2.1. Transmitting data ......................................................80
4.6.2.2. Receiving data ..........................................................82
4.6.3. Delay and timer functions..................................................83
4.6.4. Status LEDs and Bumpers..................................................86
4.6.5. Read ADC values (Battery, Motorcurrent and Light sensors)....91
4.6.6. ACS – Anti Collision System...............................................93
4.6.7. IRCOMM and RC5 Functions...............................................95
4.6.8. Power saving functions......................................................97
4.6.9. Drive system functions......................................................97
4.6.10. task_RP6System().........................................................103
4.6.11. I²C Bus Functions..........................................................104
4.6.11.1. I²C Slave ..............................................................104
4.6.11.2. I²C Master ............................................................107
4.7. Example Programs ............................................................... 111
5. Experiment Board ...................................................................... 123
6. Closing words ............................................................................ 124
APPENDIX .................................................................................... 125
A - Troubleshooting......................................................................125
B – Encoder calibration.................................................................133
C – Connector pinouts..................................................................135
D – Recycling and Safety instructions.............................................138
RP6 ROBOT SYSTEM - 1. Introduction
1. Introduction
The RP6 is a low cost autonomous mobile robot system, designed for beginners as
well as experienced electronics and software developers as an introduction to the
fascinating world of robotics.
The robot is delivered completely assembled. Thus it is very well suited for all users
who are unexperienced with soldering and tinkering and want to concentrate on software development. However, implementing your own circuits and adding additional
things to the robot is easily possible, too! In fact, the RP6 offers a lot of expansion
possibilities and may be used as a platform for a variety of interesting electronic experiments!
It is the successor of the very popular "C-Control Robby RP5", which had been released in 2003 by Conrad Electronic SE. The shortcut “RP5” is to be interpreted as
"Robot Project 5". The new robot and the predecessor system do not have too much
in common except for the mechanics. The C-Control 1 Microcontroller of Conrad Electronic has been replaced and thus the new robot cannot be programmed in Basic anymore. Instead, the far more powerful ATMEGA32 from Atmel, which is programmable
in C is used. Additionally there is an expansion module for adapting the newer C-Control PRO modules (e.g. CC-PRO MEGA128) to the robot. This module allows the system to be programmed in the more simple Basic language and provides a great number of additional interfaces and lots of additional memory.
The new design includes an USB interface, a new expansion system with improved
assembly options, high resolution odometry sensors (resolution is 150x higher compared to the predecessor system), a precise voltage regulator (this was only provided
as an expansion module for the old system), a bumper composed of two microswitches with long levers and many other things.
Basically the mechanical design has been adopted from the RP5 system. However, we
did optimize the design for lower noise operation and now it provides some additional
drilling holes for mechanical expansions.
The RP6 robot has been designed to be compatible with our other robots, ASURO and
YETI, both using the smaller ATMEGA8 and identical development tools (WinAVR, avrgcc). In contrast, ASURO and YETI are delivered as do-it-yourself construction kits
and have to be assembled by the user. The RP6 has been designed for the more demanding users, looking for good expansion options, bigger microcontrollers and more
sensors.
Beginning of 2012 the original RP6 (which was released in 2007) got a small refresh
and is now called RP6v2. The System itself did not require many changes, so the intention was not to develop a completely new Robot, but only to improve some details.
For more information take a look at chapter 1.4!
Several expansion modules are already available and can be used for expanding the
robot's capabilities. For example, there is the previously mentioned C-Control expansion, an expansion module providing an extra ATMEGA32 and of course the experiment expansion board for individual electronic circuitry. Soon there will be a Wireless
LAN Expansion module with the very large ATMEGA2560.
We wish you a lot of fun and success with your RP6 Robot System!
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RP6 ROBOT SYSTEM - 1. Introduction
1.1. Technical support
You may contact our support team via internet as follows (please read
this manual completely before contacting the support! Reading
the manual carefully will answer most of your possible questions
already! Please also read appendix A – Troubleshooting):
- through our forum: http://www.arexx.com/forum/
- by E-Mail: info@arexx.nl
You will find our postal address in the legal notice at the beginning of
this manual.
All software updates, new versions of this manual
and further informations will be published on our
homepage:
http://www.arexx.com/
and on the robot's homepage:
http://www.arexx.com/rp6
1.2. Scope of delivery – RP6
You should find the following items in your RP6 box (RP6v2 s. next page):
● Completely assembled Robot
● RP6 USB Interface
● USB A->B cable
● 10pin flat cable
● RP6 CD-ROM
● Quickstart manual
● RP6 Experiment board
● 4 pcs 25mm M3 distance bolts
● 4 pcs M3 screws
● 4 pcs M3 nuts
● 4 pcs 14pin connectors
● 2 pcs 14pin flat cable
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RP6 ROBOT SYSTEM - 1. Introduction
1.3. Scope of delivery - RP6v2
You should find the following items in your RP6v2 box:
● Completely assembled Robot
● RP6 USB Interface
● USB A->B cable
● 10pin flat cable
● RP6 CD-ROM
● Quickstart manual
Experiment board
NOT included!
1.4. The RP6v2 and Expansion possibilities
The RP6v2 is a slightly improved Version of the orignial RP6. There are new Encoders
and more expansion connectors and some other small improvements.
The main change are the new
Encoders. On the original RP6
the Encoders had to be adjusted to deliver a correct signal.
This was done in the factory,
but after shipping it could easily
happen that these had to be readjusted by the user. With the
new Encoder electronics, this is
no longer required (in rare
cases a readjustment may be
neccessary, but this is quite
simple now due to larger and
easier to access Potentiometers). The stickers with the encoder pattern are now made of
a more robust material and
have higher contrast, which increases the signal quality and
increases adjustment tolerence.
The motor and encoder cables
were directly soldered onto the
mainboard on the RP6. Now
these have connectors and can
be easily disconnected, which allows usage of the Chassis and Mainboard seperate
from each other (the RP6 already had these connectors since 2010). This makes it
easier to solder your own circuits to the Mainboard as it is more convenient to handle
without the whole chassis connected to it. In case of any defects, a replacement does
not require soldering anymore and repairing is easier.
There are now 9 additional connectors / pinheaders on the mainboard that offer various additional expansions options (s. appendix). Four of these have been there on the
RP6 as well, but were unpopulated and had to be soldered by the User.
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RP6 ROBOT SYSTEM - 1. Introduction
The main fuse has been changed from 2.5A to 3.15A, as there are now some additional power supply connectors and the power distribution has been improved. This allows
usage of slightly higher power expansions. The Motor Drivers have been improved
with new more powerful and more reliable MOSFETs. These have even lower resistance than the ones used before.
All these modifications increase the cost significantly. Over the last few years there
were also lots of increases in production cost, thus we can not include a Experiment
Expansion Board for free any longer, this has to be purchased seperately. The rest of
the Robot has not changed much, in order to keep the Software 100% compatible. If
you need more processing power or additional I/Os, you can choose frome three expansion boards: the RP6-M32, the RP6-CC128 and the new
RP6v2-M256-WIFI. These provide a lot of additional processing power and lots of interfaces for sensors and actors.
The RP6-M32 is the lowest cost option and adds another ATMEGA32, which runs at
twice the clock speed as the one on the Robot Base and has several free I/O ports. It
is also very well suited as an addtion to the two bigger expansion modules if the processing power of one of these alone is not sufficient for certain sensors or one needs
more I/O.
The RP6-CC128 module allows you to use a C-Control PRO MEGA128 Unit from Conrad
Electronic together with 64KB external SRAM. It comes with a quite comfortable IDE
and allows to use CompactC or BASIC as programming language.
The most powerful expansion module is the new RP6v2-M256-WIFI which will be released in 2012. Beneath the large ATMEGA2560 (16MHz, 256KB Flash, 8K SRAM) it
also contains a 2.4GHz 802.11g WLAN radio module. This allows you to monitor, control and remotely program the RP6 via a wireless computer network. The module features 60 free I/O Ports with lots of special purpose interfaces like several ADC, PWM,
SPI and UART channels. With all these I/Os you can virtually use any sensor and
actor combination on the RP6. The microSD Card slot allows to add large data
storage of > 2GByte (e.g. for maps, data logging, websites, etc.).
On the two images on this page you can see the RP6 with two expansion
modules (Experiment PCB and RP6-M32 with LCD) and the new RP6v2 with RP6v2M256-WIFI (of course it can also be used on the old RP6!), Antenna and LCD. The new
connectors are shown in more detail in the appendix.
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RP6 ROBOT SYSTEM - 1. Introduction
It is possible to combine the RP6v2-M256-WIFI, RP6-M32 and several of the experiment PCBs – in total you would then have a Robot with 3 AVR Processors and around
80 I/O Ports for your applications. These can be connected to the Experiment PCBs via
flat cables, where you can add your own sensor electronics or ready to use sensor
modules (e.g. Ultrasonic or Infrared Rangers, Temperature, etc.). In such a setup the
strongest processor takes control of the Robot as I2C Bus master and the other two
are used as I2C Bus slaves.
For the sake of completeness it shall be mentioned that the C-Control Unit is currently
not able to be used as a I2C Bus Slave. This means the combination of several processor modules requires the CC128 to be the I2C Busmaster. Combining the M256
and CC128 Boards is not really supported. It is theoretically possible if you use the
normal serial port (or one of the secondary ports) to command the CC128 Unit from
the M256 and put the I2C Bus into slave mode on the M256 - or not use the I2C Bus
on the C-Control Unit at all and deactivate that port.
For more information on the expansion modules, check the RP6 Website. There you
can find all related documentation and software.
Here we would like to repeat the note about the RP6 Website (this note in section 1.1
has often been overlooked in the past):
The CD-ROM can only be updated very rarely (if at all).
Software and Documentation Updates can only be found on our
Homepage:
http://www.arexx.com/
and on the robot's homepage:
http://www.arexx.com/rp6
Before you install any Software from the CD, you should check
for new Versions on the Internet!
And remember the note from the beginning of this manual:
FIRST install the USB Driver,
THEN attach the USB Interface!
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RP6 ROBOT SYSTEM - 1. Introduction
1.5. Features and technical Data
This section provides an overview of the robot's features and an introduction of some
basic keywords, to make you familiar with the terminology used in this manual. Most
of these keywords will be explained in later chapters.
Features, components and technical data of the RP6 and RP6v2:
● Powerful Atmel ATMEGA32 8-Bit Microcontroller
◊ Speed 8 MIPS (=8 Million Instructions per Second) at 8MHz clock frequency
◊ Memory: 32KB Flash ROM, 2KB SRAM, 1KB EEPROM
◊ Freely programmable in C (using WinAVR / avr-gcc)!
◊ ... and many more features! Further details will be given in chapter 2.
● Flexible expansion system, based on the I²C-Bus
◊ Only two signals required (TWI -> "Two Wire Interface")
◊ Transfer speed up to 400kBit/s
◊ Master->Slave architecture
◊ Up to 127 Slaves may be connected to the bus simultaneously
◊ Very popular bus system. The market provides a lot of standard ICs, sensors and
other components, which may often be connected directly.
● Symmetrical mounting possibilities for expansion modules at front and rear
◊ Theoretically you may stack any number of expansion modules, but the supply
capability and the overall weight allows a maximum of about 6 to 8 modules
(3 to 4 modules each at front and rear).
◊ The mainboard provides 22 free 3.2mm mounting holes and the chassis provides
another 16, summing up to 38 mounting holes in total – additionally the chassis
provides ample space for individual drills.
● USB PC Interface for program uploads from PC to microcontroller
◊ Wired connection for maximum transfer speed. Program upload will usually run at
500kBaud, filling the total free memory space (30KB, 2KB are reserved for the
Bootloader) within seconds.
◊ The interface may be used for programming all available expansion modules for
the RP6 with AVR Microcontrollers.
◊ It may be used for communication between the robot and expansion modules. For
example you can use this for debugging purposes by transferring measurement
data, text messages and other data to the PC.
◊ The interface driver provides a virtual comport (VCP) for all popular operating sys-
tems including Windows 2K/XP/Vista and Linux. The VCP can be used in standard
terminal programs and customized software.
◊ The RobotLoader Software (previous name was RP6Loader) for Windows and
Linux allows comfortable program uploads. It also contains a small terminal for
communicating with the robot through text messages.
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RP6 ROBOT SYSTEM - 1. Introduction
● Powerful caterpillar drive unit in combination with a new gearing system for
minimising noise (compared to the predecessor CCRP5...)
◊ Two powerful 7.2V DC-Motors
◊ Maximum speed ca. 25 cm/s – depending on charge state and quality of batteries,
total weight and other conditions!
◊ Self-lubing, sintered bearings at all four 4mm wheel-axles
◊ Two rubber tracks
◊ Capable of traversing small obstacles (up to ca. 2 cm height) like carpet edges,
thresholds or ramps of up to 30% steepness (with mounted bumper switches).
Removing the bumpers and restricting the number of modules to a maximum of 2
modules allows the robot to drive over ramps with up to 40% steepness.
● Two powerful MOSFET Motordrivers (H-Bridges)
◊ Rotational velocity and direction can be controlled by the Microcontroller system.
◊ Two current sensors providing a measurement range up to ca. 1.8A for each
motor. This allows to quickly sense blocked or heavily loaded motors.
◊ MOSFET Drivers have been slightly improved on RP6v2 (lower loss, more robust)
● Two high resolution encoders for speed- and motion-control
◊ Resolution 625 CPR ("Counts Per Revolution") which implies the system counts
625 segments of the codewheel per revolution of a wheel! (150x higher resolution
compared to the predecessor system CCRP5 with only ca. 4 CPR).
◊ Exact and fast speed measurement and control!
◊ High resolution of ca. 0.25mm per counted segment!
◊ RP6v2 features Encoders with improved electronics and new codewheels!
● Anti-collision-system (ACS) which can detect obstacles with an integrated IR
receiver and two IR diodes aligned to left and right
◊ Detects obstacles in the middle, left or right of the robot's front.
◊ Sensitivity and transmitter power are adjustable, allowing reliable detection of
badly reflecting objects.
● Infrared Communication-system (IRCOMM)
◊ Receives signals of standard universal infrared Remote Controls of TVs or Video
recoders. You may control your robot with a standard (RC5-) remote control! The
protocol may be changed in software, but we provide only an implementation of
the standard RC5-protocoll by default.
◊ May be used for communication with several robots (using direct line of sight or
reflections from the ceiling and walls) or for transmitting telemetry data.
● Two light sensors – e.g. for light intensity measurement and light source tracking
● Two bumper sensors for collision detection
● 6 Status LED's – for sensor and program status displays
◊ 4 of the LED Ports can also be used for other functions if necessary!
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RP6 ROBOT SYSTEM - 1. Introduction
● Two free Analog to Digital Converter (ADC) Channels for external sensor
systems (Alternatively useable as standard I/O Pins).
● Accurate 5V voltage regulation
◊ Maximum current supply: 1.5A
◊ Large copper-area for heat dissipation to the PCB
◊ Constant current should not get higher than 1A. More than this requires extra
cooling! We recommend a maximum constant current value below 800mA.
● Replaceable 2.5A fuse on RP6 and 3.15 A fuse on RP6v2
● Low standby current of less than 5mA (1mA typ. and ca. 17 up to 40mA in use,
of course this depends on system load and activity (LEDs, Sensors etc.). These
values only include electronic circuits and do not take motors and expansion
modules into account!).
● Power supply with 6 NiMH Mignon accumulator batteries (not included!)
◊ E.g. Panasonic or Sanyo (NiMH, 1.2V, 2500mAh, HR-3U , Size AA HR6) or Ener-
gizer (NiMH, 1.2V, 2500mAh, NH15-AA)
◊ Size AA, e.g. Sanyo (NiMH, 1.2V, 2500mAh, HR-3U), Sanyo Eneloop (High Capa-
city XX, 2500mAh, HR-3UWX) or Panasonic Infinium or Energizer (NiMH, 1.2V,
2500mAh, NH15-AA) or similar, minimum 2000mAh.
◊ Operating time ca. 3 up to 6 hours depending on usage and quality/capacity of
the batteries (if the engines are not being activated too much, the robot may be
operated a lot longer. These operating time specifications are only for the robot
system itself, without expansion modules).
● Connector for external battery chargers – the robot's main power switch
toggles between “Charge/Off” and “Operate/On”.
◊ This may be adapted by using a few solder pads on the PCB, allowing you to
connect the robot with external power supplies or additional batteries.
◊ Any external chargers that are suitable of charging 6 NiMH Cells in series may be
used. External chargers drastically vary in performance and additional options,
providing charging times between 3 and 14h. You need a charger with round
5.5mm plug.
● The Mainboard provides 6 small expansion areas (and additionally 2 very tiny
areas on the small sensor PCB on the front) for your own sensor circuits, e.g. for
implementing additional IR sensors to improve obstacle detection. Expansion areas
may also be used for mounting purposes, e.g. for fixing mechanical objects.
● Lots of expansion possibilities!
Furthermore we supply quite a few C example programs and an extensive function library, for comfortable software development.
The robot's Website will soon provide additional programs and software updates for
the robot system and its expansion modules. Of course we invite you to share your
own programs with other RP6 users via internet. The RP6Library and the example program files are released under the Open Source Licence GPL!
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RP6 ROBOT SYSTEM - 1. Introduction
1.6. What can the RP6 do?
Well, directly taken out of the box – not much!
It is the Software which enables the RP6 to actually do something – what this is exactly, is up to you and your creativity to teach the robot how to perform. The attraction of robotics bases on the fascinating process of implementing new ideas or optimizing and improving excisting things! Of course you may start by simply executing and
modifying the prepared sample programs to have a look at the standard features, but
it is not limited to that!
The following list mentiones only a few examples and it is up to you to expand the
RP6. There are hundreds of possibilities (s. next page for example).
Basically the RP6 can …:
● ... cruise around autonomously (this means independently, without remote control)
● ... avoid obstacles
● ... follow light sources and measure light intensity
● ... detect collisions, blocked engines, low battery level and react properly on that
● ... measure and control the rotational speed of the motors – virtually independently
of the power level of batteries, weight, etc. (this is performed with the high resolution encoders)
● ... move for a given distance, rotate for specific angles and measure the driven dis-
tance (see chapter 2 for deviations)
● ... move geometric figures, e.g. circles, polygons and others
● ... exchange data with other robots or devices. Commands may be received from
standard TV/Video/HiFi remote controls and you will be able to control your robot
just like a remote controlled car.
● ... transfer sensor data and other data to a PC with the USB Interface
● ... be expanded easily by using the flexible bus-system!
● ... modified according to your ideas. Just have a look at the schematics on the CD
and the PCB! But please restrict modifications to those you fully understand! It is
usually a better idea to start off by using an expansion board – particularly if you
are unexperienced in soldering circuits and electronics in general.
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RP6 ROBOT SYSTEM - 1. Introduction
1.7. Application proposals and ideas
The RP6 has been designed with good expansion possibilities. If you equip your RP6
with some additional sensor circuits, you can “teach” your Robot some of the following
things (some of the following tasks will turn out to be quite complex and the list is
roughly sorted in order of complexity):
● Expand the robot with additional controllers providing more CPU power, add addi-
tional memory or simply some I/O-ports and ADCs as it will be discussed in the example programs with simple I²C port expanders and ADCs.
● Output sensor data and text on a LC-Display
● React on noise and generate acoustic signals
● Measuring the distance to obstacles with additional ultrasonic sensors, infrared-
sensors or similar in order to achieve better collision avoidance
● Track black lines on the floor
● Track and trace other robots or objects
● Control the robot from your PC by using infrared signals (this needs extra hardware.
Unfortunately it does not work with standard IRDA interfaces). Alternatively you
might start straight away by using wireless RF modules.
● Control the RP6 by using a PDA or Smartphone (in this case we suggest to mount
these devices to the robot instead of using them as remote control. But that is possible, too!)
● Collect objects (e.g. tea lights, marbles, tiny metal objects …)
● Attach a tiny robot arm to grasp objects
● Navigate with the help of an electronic compass and/or infrared beacons (made up
of small towers equipped with a number of IR-LEDs and positioned at a well known
location), in order to determine the robot's position and head for a given location.
● Providing a number of robots equipped with a ball kick and handling mechanism and
some extra sensors you might be able to raise a team of robots playing soccer!
● … anything else, which might come to your thoughts!
However, first of all you have to read this manual and become familiar with robotics
and programming. The previous list of ideas is just meant as a little motivation.
And if programming does not succeed at first glance, please do not give up immeadiately and throw everything out of the window: all beginnings are difficult!
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
2. The RP6 in detail
This chapter describes the most important hardware components of the RP6 ROBOT
SYSTEM. We will discuss the electronics, the microcontroller and the interaction of
software and hardware. If you are already familiar with microcontroller technology
and electronics, you will probably just glance through this chapter. Beginners in robotics however should study this chapter to gain insight to the RP6 basics.
If you do not want to wait and rather like to test the robot, then please proceed to
chapter 3, but return to this chapter later on as it certainly contains a number of useful explanations of the robot's programming details. And you do want to know what is
controlled with the software and how this works, don't you?
We will not go deeply into details, but still a few topics in this chapter might be hard
to understand – the author tried to explain things as simple as possible.
If you wish to study special topics in detail you may also look for additional information at http://www.wikipedia.org/, which definitely is a good starting point for most
topics.
Images often tell more than words and that is why we start with an overview diagram
of the RP6. The diagram shows a drastically simplified schematic of the robot's electronic components and how they are connected together:
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
We can divide the Robot in five main functional units:
● Control System
● Power Supply
● Sensors, IR Communication and Displays (Sensors) – everything communicating
with the outside world and measureing physical values.
● Drive System
● Expansion System
2.1. Control System
As you can see in the diagram, the robot's central unit is an
ATMEL ATMEGA32 8-Bit Microcontroller (see fig.).
A microcontroller is a complete computer in a single chip. This
microcontroller differs from bigger computers (e.g. your PC) by
providing less peripherals than the big ones. Of course, the tiny
processor does not have a normal hard disk drive and Gigabytes
of RAM. A microcontroller does not need that much memory.
The MEGA32 provides “only” 32KB (32768 Bytes) Flash
ROM – which might be compared to a normal “hard disk drive” - or nowadays a flashdrive. This Flash ROM is used to store all program data. The Random Access Memory
(RAM) size is limited to 2KB (2048 Bytes) and is already more than sufficient for our
needs. Imagine for comparison the controller of the old CCRP5 Robot with only 240
Bytes RAM, which was almost completely reserved for the Basic Interpreter.
But what on earth enables a microcontroller to work with this tiny memory capacity?
That's simple: The processor neither handles huge amounts of data nor does it need
to provide an operating system such as Linux or even Windows and it does not need
to show a complex graphical interface or serve similar tasks. There will be just one
program running and that's our own one!
These limitations are by no way a disadvantage, but one of the main advantages of
microcontroller systems compared to large computers (additionally we may include
power consumption, size and cost)! The processor is designed to handle jobs in known
time slots (also called “realtime”). Usually we do not have to share the processor's
power with a great number of processes as in a standard PC and programmers are
able to carefully determine the time slot for any special function module.
The RP6 controller runs at 8MHz, which enables a processing speed of 8 Million instructions per second. The processor would even allow up to 16MHz clock, but we use
the slower clocking option which allows some power savings. The machine is still fast
enough for all of our standard jobs! Again we are comparing to the controller of the
old predecessor CCRP5 with a 4MHz clock, allowing only approximately 1000 (interpreted) Basic instructions per second. For this reason the ACS control had to be managed by another slave controller on that old Robot – we do not need this slave processor anymore! And whoever needs more processor power may add one or more
controllers to the expansion interface. The additionally available RP6 Control M32 Expansion module provides an additional MEGA32, which is clocked with the maximum
16MHz clock frequency.
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
The controller is communicating to the world outside via 32 I/O Pins ("Input/Output
Pins"), organized in "Ports", each composed of 8 I/O Pins. This way the MEGA32
provides 4 "Ports": PORTA to PORTD. The controller is able to read the logical status
of these ports and process the information in software. Of course, the processor will
equally use the ports to output logical signals in order to control small loads up to 20
mA currents (e.g. LEDs).
Additionally the controller provides a number of integrated hardware modules for special tasks. Implementing these tasks in software would normally be either very difficult or even impossible. One of these special tasks is timing. Three Timers for counting clock periods are available. The timer modules are completely independent from
program flow. In fact, the microcontroller may even process other jobs while waiting
for a programmed counter level.
RP6 is using one of the timers to generate PWM signals (PWM="Pulse Width Modulation") for speed-control of the motors and as soon as the timer has received appropriate input parameters it will manage this task in background. We will discuss more details of the PWM signal generation in the chapter “Drive System”.
For example some other modules of the MEGA32 are:
● A serial interface (UART) for PC-communication with the RP6 USB Interface. Using
this interface you might also connect another microcontroller with an UART, as long
as the USB Interface is not connected.
● The "TWI"-module (="Two Wire Interface") providing the I²C Bus for expansion
modules.
● An Analog-to-Digital Converter (ADC) providing 8 input-channels for measuring
voltages with 10bit resolution. RP6 is using the ADC for monitoring the battery
voltage level, motor current-sensors and light intensity with two light-dependant
resistors.
● Three external interrupt inputs for generating interrupt signals, which will interrupt
the program flow in the controller and force the program to jump to a special "Interrupt Service Routine". The microcontroller will then process this routine immeadiately and return back to the normal program. We will be using this programming
feature for the odometry sensors. We will discuss this sensor in detail later on.
The integrated hardware modules do not have their own individual pins, but may be
used alternatively instead of standard I/O Pins. Normally you may freely choose these
special function mapping for the I/O Pins, but the RP6 almost completely provides a
standard configuration (as it is hard-wired to all components) for pins and modifying
the standard configuration will hardly be useful.
The MEGA32 provides a lot of other things, which cannot be described in detail in this manual. You get more information on this in
the datasheet of the manufacturer (which can be found on the RP6
CD-ROM and on our Website).
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
2.1.1. Bootloader
There is a so called Bootloader located in a special memory area of the
microcontroller. This tiny program is responsible for loading new user programs into
the microcontroller's memory via the serial interface. The Bootloader communicates
with the the RobotLoader software (original name was RP6Loader) on the host PC.
Like this, no additional programming hardware is required. The USB Interface can be
used for communication with the controller through text messages and additionally to
program the controller. However there is one drawback in using a Bootloader: it needs
2KB of the flash memory, which will leave 30KB free memory for your own programs.
This does not bother us too much as there is plenty of room even for very complex
programs (compared to the 7KB free memory of the tiny ASURO robot)!
2.2. Power Supply
Of course the robot needs energy. The RP6 is carrying this energy in form of 6 accumulator batteries. Operating time will heavily depend on battery capacity and although the electronic systems will consume relatively small amounts of energy the
bulk load of energy will end up in the motors, depending on their load.
In order to provide long operating times you might favour batteries with ample capacities of up to 2500mAh. Capacities of 2000mAh however will be useable as well. High
quality batteries will provide between 3 to 6 operating hours, depending on motor
load and battery quality. You will need 6 batteries, summing up to a voltage of 6x
1.2V = 7.2Volts. The block schematic diagram labels this battery voltage "UB" (= "UBattery", U is the standard letter for voltage in electrical engineering formulas). "UB"
is defined as a nominal voltage only, as the voltage may vary over time. Completely
charged NiMH batteries can deliver up to 8.5V! The voltage drops while the Battery is
discharged and may change drastically, depending on load and quality as well. The
critical value for this is the internal resistance.
Of course, an altering supply voltage is not useable for sensor measurements. More
important however is the limited operating voltage range of semiconductor components. The microcontroller for instance might be destroyed by applying voltages too
high over 5V. Therefore we have to reduce and stabilize the voltage level to a well
defined level.
This is performed by an integrated voltage regulator capable of
supplying a current up to 1.5A (see figure). At 1.5A this device
would dissipate a lot of heat and therefore it is attached to a
large copper plane on the PCB. Even with this heat sink we sug-
gest to limit currents over 1A to a few seconds only. Otherwise
you will have to attach an additional heat sink.
Continuous current load should be limited to about 800mA. Such
a heavy load would quickly discharge batteries anyway.
Under normal load conditions and without expansion modules
the robot will not draw more than 40mA, unless the IRCOMM
transmitter is active. This current level will not cause any problems for the regulator
and it can supply enough power for lots of expansion board. Usually the expansions
will need something in the range of 50mA, if no motor loads, power LEDs, etc. are
used on them.
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
10V
1024
= 9.765625mV
2.3. Sensors
Most sensors have been mentioned in preceding chapters, but now we will have a
closer look at them.
In the overview diagram you will find sensors outside of the blue-coloured area
“Sensors”. Actually these sensors belong to other modules. However, the odometry
encoders, the motor current sensors and the battery voltage sensor are sensors and
will be discussed in this chapter, too!
2.3.1. Battery Voltage Sensor
Basically this sensor is a simple voltage divider consisting of two resistors in series.
We can assume to have a set of batteries with a maximum voltage of 10V. 6 NiMH
batteries will certainly never exceed this level. The ADC reference voltage, which is
compared to the monitored voltage, is set to 5V. The maximum 5V operating voltage
of the Microcontroller must not be exceeded at any time. For this reason the monitored voltage will have to be divided by 2. To achieve this we use the voltage divider
with two resistors, matching the monitored voltage to the ADC's voltage range.
The ADC measures the voltage at a resolution of 10 Bits (which implies a value range
between 0 and 1023 units), resulting in a voltage resolution of
A measurement value of 512 units corresponds to 5V and 1023 to approximately 10V!
These limits are usually not reached with 6 normal NiMH batteries!
The measurement is not too accurate, as we are not using precision resistors. A few
percent tolerance has to be taken into account. The reference voltage is not accurate
as well and may be fluctuating in heavy load conditions. We do not care about these
tolerances, as we only need an indicator for checking the discharging limit of the batteries. If you need to determine the exact voltages, you will need to use a Multimeter
to check the exact voltage values and then add correction values in software.
If you can accept tolerances you may even directly estimate the voltage from the ADC
value: 720 units are corresponding roughly to 7.2V, 700 to 7.0V and 650 to 6.5V. A
value of constantly 560 can be considered as empty batteries.
2.3.2. Light Sensors (LDRs)
At the front side of a small sensor-PCB you may spot two socalled LDRs (="Light Dependant Resistors"), which are aligned to
the left and to the right respectively. There is a black partition
wall between the two sensors in order to prevent light entering
the “wrong” side of the light sensor system. Just like the Voltage
sensor, both light sensors form a voltage divider together with a
resistor, but here to determine the light intensity. In this case, the 5V rail is divided as
well, but now we have a variable resistor. The division relation will change according
to the surrounding light intensity and provide a light dependant voltage level to one of
the ADC channels!
.
The voltage difference between both sensors may be used to determine at which side
of the robot the brightest source of light is located: left, right or in the middle. A suitable program can trace a bright torch in a darkened room or guide the robot to the
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
brightest spot in the room! For example if you illuminate the floor with a very bright
halogen-torch, the robot will follow the bright light spot on the floor.
Of course you may try the opposite: the robot could be programmed to hide from
bright light sources.
You can refine this by mounting one or two additional LDRs at the backside of the robot. By using only the two sensors which robot has by default, it can not distinguish
between bright light in the front and in the back too well. Two of the A/D-converter
channels are still free...
2.3.3. Anti Collision System (ACS)
From the software's point of view, the most complex Sensor is the
ACS – the “Anti Collision System”! The ACS consists of an integrated
infrared (IR)-receiver circuit (see fig.) and two IR LEDs, located at
the left and right front-side of the sensor PCB. The Microcontroller is
controlling the IR-LEDs directly. The controlling functions can be
changed and improved by yourself if necessary! The predecessor
model had a special controller for this purpose and the user could not
modify the software of this device.
The IR LEDs are transmitting short infrared pulses modulated with
36kHz, which can be detected by the IR-receiver. Whenever IRpulses are reflected by an object and received back by the IR-receiver, the microcontroller may react to the situation and start an escape manoeuvre. In order to avoid
too much sensitivity, the ACS routines will delay detection events until the system has
received a predefined number of pulses within a small period of time. Additionally, the
ACS synchronizes the detection with the RC5-receiver routines and will not react on
RC5-signals from TV/Hifi remote controls. Other codes however may interfere with the
ACS and the robot may try to avoid non-existent obstacles!
Given that the ACS has one IR LED aligned to the left and one to the right, it can
roughly determine whether the obstacle is in the middle, left or right.
The system allows you to change the pulsed intensity of both IR LEDs at three levels.
But even at the highest current level, the ACS may not detect all obstacles reliably.
This is greatly dependant on surface reflectivity of the obstacles!
Of course a black object will reflect less IR-light compared to a white obstacle and a
reflecting square-edged object may lead the IR-light mainly into a few special directions. Therefore the ACS range is drastically depend on obstacle-surface! This dependency must be considered as a basic drawback of all IR-sensor systems (at least in this
price-class).
However the robot can detect and avoid most obstacles flawlessly. If ACS-detection
fails, there are still the bumpers with touch sensor elements. And if the touch sensors
fails the robot may detect motor blocking by its current sensors or encoders!
If you are not satisfied with these sensor systems, you might consider mounting some
ultrasonic sensors for example.
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
U=R⋅I
2.3.4. Bumpers
There is a small PCB with two micro switches with long levers mounted in front of the
Robot. It protects the IR LEDs on the sensor-PCB from being damaged if the robot accidently hits an obstacle. With these switches the Microcontroller can detect collisions
and reverse the robot's direction, turn around and then go on with moving forwards.
The switches are connected to ports already used by LEDs. Thus they do not occupy
free ports of the Microcontroller. These dual usage causes the LEDs to light up as soon
as one of the switches is pressed down! However, the switches will only be hit occasionally and activated LEDs will not disturb anything then.
The bumper PCB may also be removed and for example replaced by a kick/collecting
device for balls or something else.
2.3.5. Motor Current Sensors
Each of the two motor current sensor circuits contains a
power resistor. Ohm's Law
tells us that the voltage
drop at a resistor is proportional to the current flow
through it!
In order to prevent excessive voltage drops at these resistors, they need to have a very small resistance value. Here
we used 0.1 Ohm.
With such a tiny value, the voltage drop is very small (0.1V at a 1A current) and has
to be amplified before the A/D-conversion can take place. This is performed by a socalled operational amplifier (opamp). The RP6 uses an opamp for each individual current sensor. The measureable current range is about 1.8A. This current results in a
voltage drop of 0.18V at the power resistor and an opamp output voltage of approximately 4V. This is the maximum output voltage for the opamp with 5V power supply.
The used power resistors are 10% tolerance types, the resistors at the opamp are 5%
ones. All components are non-precision components and you may observe measurement deviations of up to 270mA if you do not calibrate this! However we only need a
roughly estimated current level to detect critical motor load conditions. The robot will
reliably detect blocked/heavily loaded motors and even defective motors or odometer
wheel sensors! DC-Motors draw more current the higher the load is (Torque). With
blocked Motors, the current gets very high for our motors. This is detected by the
Software and an emergency shutdown is initiated. If this would not be done, the Motors would get very hot and and this (and the high torque) damages them over time.
If an encoder fails – whatever may have caused this - the system can reliably detect
this condition, too. Of course, the measured velocity would be zero. But if the motor
drivers run at full power and the current sensors detect only low currents (which implies that the motors are not blocked!) you may conclude either motor or encoder failure or both. For example such a condition can arise if you forget to activate the
sensors in software ...
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
50
12
⋅
50
12
=17
13
36
; 17
13
36
⋅36=625
2.3.6. Encoders
The encoders work completely different compared to the
previously discussed sensors. They consist of reflective interrupters and code wheels which are attached to one of
the gearwheels in each gearing system. This setup is used
to determine the rotational velocity of the Motors. Both encoder wheels have 36 segments (18 black and 18 white
fields, see figure). While the gears rotate, these segments
move along in front of the reflective interrupter. The white
segments reflect the IR-Light, whereas the black ones will
only refelct a minor amount of light. Just like the other
sensors the encoders produce an analog signal, but it will
be interpreted digitally. First of all the signal has to be
amplified and subsequently converted to a square wave signal by a so-called Schmitt
Trigger. Both rising and falling edges of the signal (changes of 5V to 0V and 0V to 5V)
trigger an interrupt event and these event are counted by software. This way the driven distance can be measured and together with a timer the rotational velocity can be
calculated.
Determination of the speed is the main application of the encoders. Encoder feedback
is the only reliable way to control the motor speed. In an uncontrolled system, the
motor speed would be depending on battery voltage, load and motor parameters. The
high resolution encoders even allow us to reliably control rather slow speeds.
Each of both cluster gears in the middle of the gearing system provide 50 teeth at the outer and 12
teeth at the smaller inner gearwheel (see figure).
The code wheels are located at the gearwheel next
to the motor pinion gear, thus we can calculate:
This is where the 36 Segments come from, because
this results in an integer number without fractional
part for a complete wheel revolution. The encoders
generate 625 egdes per revolution and whereas each represents one segment.
A wheel diameter of around 50mm including the rubber track theoretically results in a
wheel circumference of approximately 157mm and thus 0.2512mm for each counting
unit of the encoders. However the tracks may get deformed under pressure or they
may get pushed into flexible surfaces. Therefore we can directly assume a maximum
of 0.25mm for each counting unit. Often we will have to apply even less: 0.24 or
0.23mm. Calibration values may be determined by driving well defined test distances
as described in the Appendix. This is not accurate because of slippery and similar effects. Moving straight forward will cause minor encoder accuracy errors, but rotating
the robot will result in increased deviations. Especially rotating the robot on the point
will cause deviations.
Deviations can only be determined and corrected by testing, trial and error. This is a
drawback for all caterpillar drive systems – in our robot and in more expensive as
well. Compared to robots with a standard differential drive unit with two wheels and
an additional support wheel the caterpillar systems allows a far better behaviour in allterrain surroundings. The caterpillar drive system will easily overcome small
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
obstacles, ramps and uneven floors. On such surfaces, the encoders are extremely
helpful, as they allow optimal speed regulation under all load conditions, completely
independent of surface condition, motor load and Battery voltage.
At a rate of 50 segments per second we have a speed of 1.25 cm/s assuming a value
of 0.25mm per segment. This speed is the minimal speed, which can be controlled
reliably (at least with the standard software implementation). The exact value may
vary for individual robots. A rate of 1200 segments/second corresponds to the maximum possible 30 cm/s (at 0.25mm resolution, whereas 0.23 corresponds to 27.6 cm/s).
Maximum speed depends on battery charging status and 30cm/s will are not possible
for too long with usual Batteries. Because of this, the function library forces a limit of
1000 segments/second to be able to maintain a constant maximum speed for longer
battery discharge periods. Additionally, the life time of gears and motors will be prolonged when using lower speeds most of the time!
Whenever the robot has counted 4000 segments, it will have covered a distance of
approximately one meter. As already explained, this specification is valid for exactly
0.25mm resolution - without proper calibration you will notice more or less severe
deviations. If you do not care for precise distance calculations, you just do not need to
calibrate the encoders and simply assume a value of 0.25mm or better 0.24mm!
Good navigation systems usually do not rely completely on encoders for distance and
angle controls, but use external fixed markers such as infrared beacons and a precision electronic compass. So it is usually a good idea to use external systems to correct
odometry deviations as often as possible.
2.4. Drive System
The RP6 drive system consists of two DC motors with attached gearing systems for
powering the caterpillar wheels (see preceding figure). The motors can consume a
fairly high amount of power and a microcontroller can not directly serve such high currents.
Thus we need powerful motor drivers. We
use two so called H-Bridges for the RP6 Motors. The diagram on the left shows the basic principle. There you can also see why it
is called like this: The Switches and the Motor form the letter “H” together.
Now let us assume all switches are open. If
we close switches S1 and S4 (red) a voltage
will be applied to the motor and it will start
turning, say to the right. If we now open S1
and S4 again and subsequently close S2 and
S3 (green), we reverse the applied voltage
and the motor will start turning in the opposite direction (to the left). Of course we
will have to take care not to close S1 and S2
or S3 and S4 simultaneously. Each of these combinations would result in a short circuit and might destroy the activated switches.
Of course the RP6-design will not be using mechanical switches but so-called
MOSFETs, which are conductive if a suitable voltage is applied to the gate connection.
MOSFETs can switch very fast at a rate of several Kilohertz is possible.
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
Now we have found a way to reverse the motor's rotational direction. And how are we
going to accelerate or slow down the motor? A DC-Motor will rotate faster the higher
the voltage gets and we may control the motor speed by increasing or decreasing the
voltage. Let's have a closer look at the H-bridge again.
The figure shows what we can do. We
generate a square wave at a fixed frequency and apply pulse width modulation,
which changes the
duty cycle. “Duty
cycle” means the ratio
between high and low
signal periods.
The motor will now get
a lower median DCvoltage, corresponding
to the duty cycle.
The graph shows this
behaviour with a red
line (Ug) and the red areas under the lines. For example if a battery voltage of 7 Volts is applied to the motor controller circuit and
the motor is being controlled at a PWM duty cycle of 50% the
equivalent median DC-voltage would be roughly 3.5 Volts! This is
not completely corresponding to the real circuit conditions, but it is
good to visualize it like this.
The RP6 uses a rather high gear reduction ratio (~ 1:72) which results in a quite
strong driving system, enabling the robot to carry heavier loads, for example compared to the small ASURO robot. However with increasing weight, we must consider a
higher power supply load, resulting in an increased discharge rate…
Compared to remote controlled racing cars you might think the RP6 is a slow
vehicle - which is true - but we designed the robot to be slow! The robot is build to be
controlled by a microcontroller and if the programmer makes a mistake in the software it would be rather unfavourable if the robot crashes into a wall at a speed of
10mph! So by using a moderate speed, the RP6 will not run into trouble that easy and
at a slower movement the sensors will have ample of time to react on obstacles. Additionally the robot is more powerful and the speed control is more accurate! Slower
speed enables the RP6 robot to drive very very slowly at a constant speed!
2.5. Expansion System
One of the most useful features of the RP6 is the expansion
system, allowing you to easily add additional things to the
Robot. The basic RP6 platform includes rather few sensors.
Still this number of sensors is well above the average of
comparable robots in this price-class, but the robot will only
become really attractive with several additional sensor modules. The ACS for example will only detect the existence of
obstacles in front of the robot. Using ultrasonic sensors or
improved additional IR-sensors you might be able to determine the distance and start sophisticated manoeuvres to avoid
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
the obstacles!
Apart from sensor circuits, additional controllers could be useful to perform additional
tasks, e.g. the RP6 CONTROL M32 providing an extra MEGA32 microcontroller.
Of course the expansion system has to be capable of connecting several expansion
modules (see figure), while using a minimum number of signal lines and providing
sufficient communication speed.
2.5.1. The I²C Bus
The I²C Bus will satisfy these requirements. The name stands for Inter Integrated
Circuit Bus and is pronounced I-squared-C. Sometimes we may write “I2C” instead of
“I²C”, because in plain C language the “²” symbol is not allowed for variable names
and other things. The bus requires only two signal lines and may connect 127 participants communicating at a rate of 400kBit/s.
The extremely popular I²C Bus, designed by Philips Semiconductors during the
eighties and nineties, is used in a great number of electronic equipment, e.g. video recorders, televisions, but also in industrial systems. Most of the modern PCs and notebooks use a variant of this bus called SMBus to control air flow and temperature of the
internal devices. A great number of robots also uses the I²C Bus system and for this
reason a number of sensor modules like ultrasonic sensors, electronic compasses,
temperature sensors and similar devices are available on the market.
The I²C Bus is a master/slave-oriented bus. One or more master devices are controlling communication with up to 127 slave devices. But even though the bus is able
to handle multi-master communication, we will only describe a bus communication
with a single master device. Multi-master topology would only complicate things.
The two required signal lines are named SDA and SCL. SDA is to be read "Serial Data"
and SCL is named "Serial Clock" – which already explains we are using a data- and a
clock signal line. SDA is used as a bidirectional signal and therefore both master and
slave devices are allowed to output data. SCL is completely controlled by the master
device.
Data bits are always transferred synchronous to the clock signal as delivered by the
master. The SDA level is only allowed to change as long as SCL is low (except for
Start- and Stop-conditions, see below). Transfer rates are allowed to change between
0 and 400kBit/s even while data is being transmitted.
The preceding figures show usual transmission protocols. The first one shows a transmission from a master to a slave device, in which white boxes refer to data transmissions from master to slave and the dark boxes represent the responses from the slave
device.
Each transmission has to start with an initial start condition and must be ended by a
stop condition. The start condition is raised whenever at a high SCL-level the data line
SDA is pulled from high to low level. A reversed level pattern applies to the stop-condition: whenever at a high SCL-level the data line SDA is pulled from low to high level
we meet a stop-condition.
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
Immediately after the start-condition we have to send the 7 Bit long slave-address for
the device to be addressed, followed by a bit defining whether we want to write or
read data. The slave will respond by sending an ACK ("Acknowledge"). Any number of
data bytes may follow and each individual received byte will have to be acknowledged
by the slave (using the ACK-signal). Communication will be terminated with a
stop-condition.
This description is only a very short explanation of the I²C Bus. Interested readers
may find more information in the I²C Bus specification sheets by Philips. And also the
specs for the MEGA32 do contain more information to this topic.
The example programs demonstrate how to use the bus hardware. The RP6 library
already provides functions for controlling the I²C Bus. You will not have to go into details of the protocol, but it is useful to understand how bus the communication is basically working.
2.5.2. Expansion Connectors
The mainboard provides four expansion connectors.
Two of these devices are labelled “XBUS1” and
“XBUS2” respectively. “XBUS” is a shortcut for “eXpansion BUS”. “XBUS1” and “XBUS2” are interconnected
completely and have been arranged symmetrically on
the main board. For this reason you will be allowed to
mount expansion modules both at front and rear of the
robot. Each expansion module provides two XBUS connectors at one side of the module. A 14-pin flat cable is used for interconnecting the modules to each other and to
the mainboard. For interconnections each expansion module provides two identical interconnected plugs. The outer plug has to be used for downward interconnections,
whereas the inner plug has to be used for upward interconnections. This way you are
(theoretically) allowed to stack any number of modules (see figure, showing three
RP6 breadboard expansion modules, which may be used for your individual circuits).
The XBUS plugs provide power supply, the previously described I²C-Bus, a master
rest and interrupt signals.
The power supply provides two voltages at the connectors: first of all the stabilized 5V
from the voltage regulator, but the battery voltage as well. The battery voltage will
vary with time and load – usually between 5.5 (discharged batteries) up to approximately 8.5V (newly charged batteries – varying from manufacturer to manufacturer).
Voltages may however exceed these limits depending on load, type and charging
status of batteries.
The master reset signal is important for resetting all microcontroller devices when
pressing the Start/Stop-button or for programming. The boot loader programs in the
microcontrollers will start their user program at a low pulse (high-low-high) on SDA.
This way all programs on the (AVR) controllers will simultaneously start after pressing
and releasing the Start/Stop-button or by starting the program by boot loader software... (the boot loader does not only generate a low impulse to start, but also a
complete I²C General Call with 0 as data byte.)
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RP6 ROBOT SYSTEM - 2. The RP6 in detail
A few modules can use the interrupt lines for signalling the master microcontroller
either the arrival of new data, or whether a job has been completed and new commands are being expected. Not providing these lines would force the master device to
repeatingly query some specific expansion modules for new data. Of course this method would be possible, but the alternative design with additional interrupt lines will
usually reduce bus traffic and CPU load. As the number of interrupt lines is restricted
to 3 signals and one free line reserved for user signals, you may have to assign one
line to several modules (e.g. all ultrasound sensors) and poll all modules subsequently
when an interrupt is signalled.
The other two expansion connectors labelled “USRBUS1” and “USRBUS2” on the mainboard are not interconnected. All lines are routed to soldering pads on all expansion
modules and you may apply your own signals to these pads.
“USRBUS” is an abbreviation of “User-Bus”. You may use this 14-pin expansion connector for anything you want - your own bus system, additional power supply lines
(but be careful, the traces are rather thin and for low currents of max. 500mA only) or
anything else. Example given: you are able to interconnect two expansion modules
without providing connections to other modules. This might be useful for more complex circuits or sensors, which cannot be placed on a single expansion module. This
method will tidy up your wiring.
Of course you can not add any number of expansion modules – 6 stacked modules at
the front- or backside will definitely overload your vehicle. Too many modules will also
cause problems by overloading the battery supply. As a general rule you may mount a
maximal number of 8 modules to the RP6: 4 at the front side and 4 at the backside.
The figure shows the connection diagram for both expansion connectors. On the mainboard, pin 1 is always located
near the white label XBUS1 and XBUS2, respectively. Alternatively, the pin is labelled with “1” at the connectorposition.
+UB is the battery-voltage, VDD is the +5V rail, GND labels “Minus” or “Ground” (GND = Ground), MRESET labels
the Master Reset Signal, INTx are the Interrupt-lines, SCL
is the clock- and SDA the data-line of the I²C Bus.
Anything else you need has to be soldered to the USRBUS
connector pins.
Important note: Do not overload the supply lines VDD and +UB! These lines
can provide a maximum current of 1A each (this applies to both Pins TOGETHER! This means joined Pins 4+6 (+UB) and 3+5 (VDD) of the connectors)!
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RP6 ROBOT SYSTEM - 3. Hardware and Software Setup
3. Hardware and Software Setup
Before you start with setting up the RP6 or accessories, you have to
read the following safety instructions carefully. Especially if children
are handling the RP6 later on!
Please read this chapter extra carefully!
3.1. Safety Instructions
Due to the open frame architecture of the RP6, there are several sharp edges. Thus
the Robot may not be used as a toy for children aged less than 8 years! Please supervise children that are in the room while operating the RP6 and inform your children
about the described dangers!
Do not operate the robot in locations with freely moving animals, for example hamsters, as they may get hurt. The other way round, bigger animals like dogs and cats
might damage the robot...
The caterpillar drive system has some dangerous sectors between tracks and
wheels, where the caterpillar may draw in you fingers. These sectors are
largely covered by the wheel wells of the RP6 and therefore mostly secure. Still, take
care not to get your fingers between wheels and tracks! The motors are quite powerful and may easily hurt you! Also keep your fingers out of the area between PCB and
tracks!
ATTENTION: Even if you are using the standard software, the motors may automatically increase their power level! Depending on the programming style, motors may
start operation at any time and unforeseen reactions and movements may occur!
Never operate the robot without supervision!
3.1.1. Electrostatic Discharges and Shorts
The surface of the main PCB, the USB Interface and all expansion modules is uncovered and reveals a great number of unprotected components and PCB traces.
Please do not cause short circuits by deposition of metallic parts or tools on the surface of the Robot!
Supply voltages are at very low levels only and safe for human beings. A great num-
ber of components however may get damaged by electrostatic discharges
(ESD) and you should not touch these components unless necessary!
Especially in combination with synthetic clothing, dry air may cause electrostatic charging of the human body. And the robot as well may be charged, mainly depending on
the floor-covering. In touching metallic parts charged bodies will be discharged by tiny
sparks. These discharges may damage or destroy electronic components while manipulating these parts. To prevent damages by ESD please touch a large grounded device
(e.g. your PC's metal housing, a drainpipe or a heating pipe) before touching the electronic components. Touching a grounded device will discharge your body. Uncontrolled
discharges of the robot touching grounded obstacles will not damage the robot, but it
may cause program crashes or unforeseen reactions.
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RP6 ROBOT SYSTEM - 3. Hardware and Software Setup
All electric lines from and to the system must be connected before connecting and applying the supply voltage.
Unexpected connecting or disconnecting plugs, cables or modules in an operating robot may damage or destroy parts of the system and additional components.
3.1.2. Environment of the Robot
Do not operate the robot on table tops or in areas with high precipies, where it may
fall down to the ground. Please consider the climbing capability of caterpillar vehicles!
The robot may easily drive over small obstacles and push light parts ayway! Please remove all objects containing liquids from the robot's operating area, e.g. cups, bottles
and vases.
The robot's chassis will protect the mechanical parts against a number of environmental influences, but it is neither water- nor dustproof. The electronics are rather
unprotected as well. You should operate the robot in clean and dry in-house areas
only. Dirt, loose particles and humidity may damage or destroy mechanical and electronic components. Operating temperatures are to be restricted between 0°C and
40°C.
Especially inside operating DC-Motors, tiny sparks are generated. Do not operate
the robot at all in an environment with combustibles or explosives (liquids, gases or
dusts)!
If not operated for long periods of time, the robot should not be stored in locations
with high humidity! Please also remove the batteries to prevent damage by leaking
batteries!
3.1.3. Supply Voltage
The robot has been designed for a 7.2V supply voltage, provided by 6 rechargeable
NiMH batteries. Maximal supply voltage is 10V and shall not be exceeded at any time.
Only use charging devices with valid and legal safety certifications for charging batteries!
As a remedy you may also operate the robot with 6 heavy duty alkaline batteries.
Normal batteries however will discharge rapidly and cause high costs and environmental damages, so please use rechargeable batteries if possible! Rechargeable batteries will also provide higher maximum currents and may easily be charged inside the
robot!
Please pay attention to the safety and disposal remarks for batteries in the
appendix!
Modifications of the robot should only be done by users, who are completely
aware of what they are doing. You may irreversibly damage the robot or
harm yourself and others by modifications (e.g. overheating components may
cause fire in your house...)!
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