TruTrak Digitrak User Manual

DigiTrak Autopilots

Installation & User Guide

8300-009 Rev B

TRUTRAK FLIGHT SYSTEMS

1500 S. Old Missouri Road

Springdale, AR 72764

Ph. 479-751-0250 Fax [phone]

www.trutrakflightsystems.com

INSTALLATION MANUAL

for

DigiTrak Autopilots

TABLE OF CONTENTS

Power Up........................................................................................................................................................1

Basic Operation..............................................................................................................................................1

Nav Mode Operation......................................................................................................................................1

Mechanical Considerations ............................................................................................................................2

Magnetic Considerations................................................................................................................................3

RFI / EMI Considerations ..............................................................................................................................3

Connecting GPS Units

GPS Setup Guide ...........................................................................................................................................3

Portable GPS’s............................................................................................................................................3

Panel mount GPS’s .....................................................................................................................................5

Ground Checkout ...........................................................................................................................................7

First Flight......................................................................................................................................................8

Magnetic Calibration......................................................................................................................................9

Definitions....................................................................................................................................................10

DigiTrak Settings .........................................................................................................................................10

Electrical Pin-out..........................................................................................................................................11

Trouble Shooting..........................................................................................................................................11

DigiTrak Wiring Diagram............................................................................................................................12

DigiTrak Block Diagram .............................................................................................................................12

Revision Date Description Page #

A 1/1/2008 Initial Release

B 10/14/09 Updated warranty and pictures 13,14,16

Power Up

NOTE: When powering up the autopilot ensure that the aircraft is as still as possible
for 10 seconds.

The power up of the autopilot takes approximately ten seconds. During the power cycle it is very important that the aircraft be
as still as possible for the initialization of the internal gyro. While the autopilot is in the power up the display will show three

flashing
valid GPS signal present the display will show three non-flashing

(“–”) characters. If there is a GPS signal present the display will now change to read (“OFF”). If there is not a

(“–”) characters.

Basic Operation

Once the aircraft is off the ground and at a safe altitude, the autopilot can be engaged. There are two ways to engage the
autopilot. Pressing the button will engage the autopilot. If a GPS signal is present, the autopilot will display the current

track and will now hold the track. If there is no GPS signal the display will show
mode instead of track hold mode. The second way to engage the autopilot is with the Control-Wheel Switch, pushing and
holding the control wheel switch for approximately 1-1/2 seconds and releasing will engage the autopilot.

Changing the selected track can be done several different ways. One way in which the track can be changed is to momentarily
push and release the
signal present momentary push and release the
heading. The second way to change the selected track is to push and hold the or button. After approximately
1-1/2 seconds the autopilot will enter a constant-rate turn. While turning, if a GPS signal is present, the display of the autopilot
will be a digital DG displaying a gyroscopically smoothened GPS track throughout the turn. When the desired track is
displayed on the autopilot, push and release the opposite
the new selected track. Note that when the button is pushed to stop the turn, the aircraft is still in a bank; therefore the
autopilot will have to stop the turn and fly back

into the constant rate turn mode, the display will show a stroboscopically-moving symbol in the direction of the selected turn.

The final way to change the selected track is with the Control-Wheel Switch. Pushing and holding the Control-Wheel Switch
will disengage the servo and the display on the autopilot will be a Digital DG .While holding the Control-Wheel Switch, fly the
aircraft manually to the desired track using the Digital DG display as a reference. Upon release of the Control-Wheel Switch,
the servo will re-engage and the autopilot will now fly the new selected track. If there is no GPS signal present the Digital DG
will not be displayed.

or button. This will result in a one-degree change in selected track. If there is no GPS

or button will result in approximately a one degree change in

or button. The autopilot will now stop the turn and fly

to the selected track. If there is no GPS signal present, and the autopilot is put

“–| – |–” and will be in “heading hold”

Disengaging the autopilot can be done in two different ways. Pressing the
second way to disengage the autopilot is with the Control-Wheel Switch. Momentarily pushing and releasing the Control­Wheel Switch will disengage the autopilot.

button will disengage the autopilot. The

Nav Mode Operation

When the autopilot is engaged and there is a flight plan present in the GPS, every 3-4 seconds the display will flash (“– F –”).
This is to alert the pilot that the autopilot is receiving a valid GPS flight plan. To enter the Nav Mode, momentarily push the

and buttons at the same time. (Take care not to hold both buttons in for too long a time, or the autopilot will
enter the setup mode instead.) The autopilot display will now begin flashing the Digital DG reading as it maneuvers to
intercept the course line at about a 45 degree angle. Once the course-line is intercepted and the autopilot has turned within a

few degrees of the desired track, the display will change from the flashing DG to
tracking the course line. Pushing any button on the autopilot will exit the Nav Mode. When on course, 1 or 2-degree
excursions are normal. When the end of the flight plan is reached or the flight plan is cancelled on the GPS unit, the autopilot
will continue flying the track it was flying when the flight plan ended. If the flight plan has multiple waypoints, the autopilot
will make the necessary turn at each waypoint. Because, typically, the information from the GPS to the autopilot does not
change until the waypoint is crossed, the autopilot will over-fly the waypoint, and then will fly back to intercept the new course
line. Some GPS units have a “turn anticipation” feature, and if this feature is enabled on the GPS the autopilot may turn prior
to reaching a given waypoint.

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(“– 0 –”) indicating that the autopilot is now

Mechanical Considerations

The installation information in this section is extremely important and must be clearly
understood by the installer. Improper servo installation or failure to observe and diagnose

installation problems prior to flight can result in extremely serious consequences, including
loss of ability to control the aircraft. If there are any questions on the part of the installer it

is mandatory to resolve these questions prior to flight of the aircraft.

Most modern experimental aircraft use push-pull tubes to drive the primary controls. These tubes generally have a total travel
of 3” or less; therefore, it is best to connect the autopilot servo to the primary control by the same method. This connection
consists of an arm on the servo connected by a push-pull rod to the primary control. Rod-end bearings are required on each
end of the push-pull rod.

The servo arm must not rotate even near to the point called OVER CENTER, the point at which the primary
aircraft control would lock up. Some aircrafts mechanical primary control installations will not allow this to

occur and do not need the servo stops.

This is a condition that would result from the servo being back driven when the pilot operates the controls, or
from the servo itself driving the controls to a stop. To protect against this mechanical stops are supplied with the
servos. These stops are drilled so that they can be mounted at different angles as required (18° intervals).

In addition to the proper use of the stop it is important to know the amount of travel on the primary control that
the servo can handle. With the push rod connected to the outermost hole (1 ½”) the travel on the primary cannot
exceed 2 ½”, the intermediate hole 2 1/16”, and the inner hole 1 5/8”.

It is important to note that the servo travel should be very nearly the same in both directions. In most cases this
means that the servo arm needs to be perpendicular to the push rod but there are exceptions such as the RV-4 and
RV-8 installations.

There will be installations in which space does not permit the use of the stop. When this is done the aircraft’s primary control
stops must be positive and care must be taken to be sure that the servo drives the push rod the same distance in both directions,
and that the travel limits of the servo arm are not exceeded.

There are installations in which the travel of the push-pull tube exceeds the allowable 2 ½”. For such installations, the drive
can be applied to a bell crank at a radius point that moves the desired 2 ½” of maximum allowed travel in the outermost hole of
the arm.

When there is no way to have a drive point of less than 2 ½” or when the primary control is cable-driven it is necessary to use
the capstan-cable servo drive. When this is done the servo should be mounted so that the 1/16” diameter cable which wraps
around the capstan when extended parallel to the primary cable is approximately 3/16” from the primary cable. If the primary
control travel does not exceed 5” the cable-locking pin will be 180° away from the point at which the cable leaves the capstan.
When the primary control is at the neutral point this means the total cable wrap around the capstan is 360°. If the primary
control travel is greater than 5” the cable wrap is 720°and the pin is adjacent to the output point when the primary control is at
the neutral point.

The cable clamps when properly installed will not slip and thus get loose, but it is desirable to nicopress or swedge a fitting on
to the cable so as to provide added assurance that the cable will not become slack. If the bridle cable is not sufficiently tight,
there will be lost motion in the autopilot drive. This will result in hunting (oscillation).

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Magnetic Considerations

Because the autopilot contains a built-in magnetometer for a backup source of heading in the event of GPS loss, it is important

to try to locate the programmer away from known sources of magnetic disturbance. The calibration procedure can account for a
moderate amount of fixed disturbance (for example, nearby iron objects) but it cannot adjust for changing magnetic fields such
as would be generated by aircraft compasses or certain electrical devices. One such source of such problems is the “Flag”
mechanism in some older DG or HSI devices. These units use a solenoid to hold the flag out of sight, and the magnetic field
will then change when the flags come and go. If at all possible, place the autopilot so as to be as far as possible from such
devices. A hand-held compass can be used to assist in finding fixed or variable disturbances prior to installation of the
autopilot. Even a few inches can make an appreciable difference in the magnetic disturbance level. It should be noted also that
strobe light controls, landing lights, navigation lighting, pitot heat, generate very strong currents in their wiring, thus they will
create a periodically pulsating magnetic field disturbance. Shielding has no effect on this problem; the only solution is to keep
wiring as far away as possible from any electronics which can be affected by pulsating magnetic fields.

RFI/EMI considerations

The autopilot programmer is shielded and does not generate any appreciable level of electromagnetic interference. Moreover,
the servo lines (except for power and ground) are low-current and cannot contribute to RF interference. The servo power and
ground lines do have switching currents through them, but so long as there are no parallel runs of servo power and ground lines
with such things as poorly-shielded antenna lines or strobe light power lines, there is no need to shield the servo harnesses.

The autopilot itself has been internally protected from RF interference and has been tested under fairly extreme conditions,
such as close proximity to transmitting antennas. However, it is always good practice to insure that such antennas are properly
shielded and not routed directly over or under sensitive panel-mounted electronic equipment. Most problems in this area are the
result of improper RF shielding on transmitting antennas, microphone cables, and the like. The most sensitive input to the
autopilot is the Control Wheel Switch input. This line should not be routed in parallel with transmitting antennas or other
sources of known RF interference. If necessary, it can be shielded with the shield connection to pin 8 of the autopilot
connector.

Specific connections for certain commonly-used in-panel GPS units

Note that the information in the tables is based upon the best information available from each manufacturer’s documentation at
the time of publication. Please consult the appropriate installation manual for confirmation of wiring information.

GPS Setup Guide

Portable GPS’s

Many new handheld GPS’s have adequate output required to fly a TruTrak autopilot. Although most support data
output not all handhelds will provide consistent and reliable information required to fly all TruTrak autopilots. Therefore,
some handhelds will not fly the airplane well. Performance may decline by putting the processor in high-load situations.

We require a data output rate of once per second for best performance. Some handhelds output data at longer intervals
than once per second. These handhelds will cause the autopilot not to perform well in turns and it may cause overshooting and
hunting. If the baud rate is selectable the optimum setting is 4800. Most handhelds will require a data cable that plugs into the
handheld and provides a medium for data output. This is an accessory and is available from your GPS manufacturer. The
setup procedures are in your GPS manual. If your GPS is not listed here consult your GPS manual for NMEA output setup.
The autopilot must have a direct connection with the handheld GPS to provide the autopilot with RS-232. To allow the
handheld GPS to be removed easily you should add a connector in your panel. We recommend that you use a 9 pin D
subminature connector in your panel that will mate to the harness from the GPS. This will also allow you to wire power and
ground and use the aircraft electrical system to power your handheld GPS.

Magellan GPS 315 A

The Magellan GPS 315 A requires a Power/Data Cable (Magellan Product Number 730276) to provide data output.
The Magellan GPS 315 A must be configured to provide the correct output to the autopilot.

Press the MENU key then select “Setup. Press ENTER. Select “NMEA” and press ENTER. Select “V2.1 GSA” then
press ENTER. Next we must set the baud rate. Press MENU then select “SETUP” and press ENTER. Next Select
“BAUD RATE” and press enter. Select 4800 for the baud rate. Press ENTER.

Garmin GPS III

The Garmin III requires a Power/data cable (Garmin Part Number 010-10082-00) to provide data output.
The Garmin III must be configured to provide the correct output to the autopilot.

Press the MENU key twice. Select ‘Setup’. Press ENTER. Select the ‘Interface’ tab. Press ENTER. Select the NMEA

format.

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GPS 92

The Garmin 92 requires a Power/data cable (Garmin Part Number 010-10082-00) to provide data output. The Garmin 92 must
be configured to provide the correct output to the autopilot.

Press the PAGE key until the ‘Main Menu’ appears. Select ‘Setup Menu’ and press ENTER. Next select ‘Interface.’
Press ENTER. Select NONE/NMEA.

Garmin GPS 195

The GPS 195 provides data output every two seconds and may be slow in recognizing turns and will overshoot the desired
track. This may cause the autopilot to wander and not perform well in turns.
The Garmin 195 requires a Power/data cable (Garmin Part Number 010-10135-00) to provide data output. The Garmin 195
must be configured to provide the correct output to the autopilot.

Press the MENU key twice. Select ‘Set-Up Menu’. Press ENTER. Select ‘Input/Output’. Press ENTER. The

input/output format is ‘No In/NMEA Out.’ Note that the baud rate is automatically set at 4800 bps.

Garmin GPS 196

The Garmin 196 requires a Power/data cable (Garmin Part Number 010-10082-00) to provide data output.
The Garmin 196 must be configured to provide the correct output to the autopilot.

Press the MENU key twice. Use the arrow keypad to select the ‘SETUP’ tab.

Within the Setup Menu select the ‘INTERFACE’ tab. Using the arrow keypad highlight the ‘Serial Data Format’ field.

Use the arrow keypad to select ‘NMEA In/NMEA Out’ and press ENTER. Set the baud rate to 4800.
Press MENU to enter the Advanced NMEA page. Select ‘Advanced NMEA Setup’ and press ENTER.
Using the arrow keypad and the ENTER key to turn OFF ‘GPS Status (GSA, GSV)’, ‘Waypoint/Route (WPL, RTE)’, and

‘GARMIN Proprietary’.

Garmin 295

The Garmin 295 requires a power/data cable (Garmin Part Number 010-10082-00) to provide data output. The Garmin 295
must be configured to provide the correct output to the autopilot.

Press the MENU key twice. Use the rocker keypad to select the ‘INTERFACE’ tab.

Press the down portion of the rocker keypad to select the ‘FORMAT’ field.

Press ENTER and a popup window will show the available settings.
Use the rocker keypad to select ‘NMEA OUT’ then press ENTER. Select 4800 for the baud rate.

Note: This is the baud rate that will need to be entered in the setup mode of the autopilot.

Now the Garmin 295 is correctly set up to provide the RS-232 serial output required by your TruTrak autopilot.

Garmin 296

The Garmin 296 must be configured to provide the correct output to the autopilot.

Press the MENU key twice. Use the rocker keypad to select the SETUP in the vertical tabs. Use the rocker keypad to

select the ‘COM 1’ tab.
Press the down portion of the rocker keypad to select the ‘FORMAT’ field.

Press ENTER and a popup window will show the available settings.
Use the rocker keypad to select ‘NMEA IN / NMEA OUT’ then press E NTER. Select 4800 for the baud rate. Note: This

is the baud rate that will need to be entered in the setup mode of the autopilot.

Press MENU to enter the Advanced NMEA page. Select ‘Advanced NMEA Setup’ and press ENTER.
Using the arrow keypad and the ENTER key to select “FAST OUTPUT” or turn OFF ‘GPS Status (GSA, GSV)’,

‘Waypoint/Route (WPL, RTE)’, and ‘GARMIN Proprietary’.

Garmin 396

The Garmin 396 must be configured to provide the correct output to the autopilot.

Press the MENU key twice. Use the rocker keypad to select the SETUP in the vertical tabs. Use the rocker keypad to

select the ‘Interface’ tab.
Press the down portion of the rocker keypad to select the ‘Serial Data Format’ field.

Press ENTER and a popup window will show the available settings.
Use the rocker keypad to select ‘NMEA IN / NMEA OUT’ then press E NTER. Select 4800 for the baud rate. Note: This

is the baud rate that will need to be entered in the setup mode of the autopilot.

Press MENU to enter the Advanced NMEA page. Select ‘Advanced NMEA Setup’ and press ENTER.
Using the arrow keypad and the ENTER key to select “FAST OUTPUT” or turn OFF ‘GPS Status (GSA, GSV)’,

‘Waypoint/Route (WPL, RTE)’, and ‘GARMIN Proprietary’.

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