TruTrak DFC Install Manual - Manual (Page 10)

DFC Autopilot Installation Manual TruTrak Flight Systems
May 2006 Printing 8
The next step in the check-out procedure is to verify that all servos run, and in the correct direction. Power up the autopilot and
wait approximately ten seconds for AP OFF to be displayed in the lower right portion of the screen. Then press and release the
ON OFF button to engage the autopilot. At this point, the selected heading will be underlined on the bottom left of the display,
while the selected vertical speed (“SVS”) will be shown on the bottom right. Use the VS UP and VS DN buttons to set
selected vertical speed to zero. The pitch servo should stop, or move only very slowly. Then press VS UP repeatedly until
several hundred feet per minute is showing on the lower right SVS field. At this point the pitch servo should be moving the
control yoke or stick back, in an effort to raise the nose of the aircraft. Similarly, using VS DN to select a negative selected
vertical speed, the pitch servo should be moving the controls in such a way as to lower the nose of the aircraft. If direction is
incorrect, install or remove the jumper between pins 1 and 2 of the autopilot connector.
The roll servo should also be responding at this time, moving the controls in such a way as to turn the aircraft from the current
heading (shown as a 3-digit number after the word MAG in the upper-left of the display) to the selected heading (shown as a 3-
digit number after the word SEL in the lower left of the display). The initial value of the selected heading is the current heading
of the aircraft at the moment of engagement, but the encoder knob can be used to modify the selected heading. When the
heading shown as SEL agrees with the heading of the aircraft shown in the top line as MAG, the roll servo should stop or run
only very slowly. If the knob is rotated clockwise, to a selected heading right of the current heading, the control yoke or stick
should move in such a way as to roll the aircraft to the right. Conversely, a selected heading to the left of the current heading
will move the controls in the opposite direction to attempt a roll towards the left. If servo direction is not correct, the wires
going to pins 4 and 5 of the roll servo (pins 32 and 33 on the main connector) must be reversed to achieve the correct response.
If the servos do not move at all, double-check the LAT TORQUE or VRT TORQUE setting as appropriate. If a servo jitters but
does not actually rotate, check the wiring on the four servo drive lines to that servo for continuity and correctness. If the servo
does not seem to have any torque, check the relevant torque control line for continuity and correctness.
At this time, check that the servo arm or capstan is properly operating the controls. For servo installations using an arm, check
that as the controls go from limit to limit the arm of the servo remains in the operating range of the servo (a maximum of 100
degrees total rotation) and that when the controls are centered, the connecting pushrod is approximately perpendicular to the
arm of the servo. For capstan systems, insure that the cabling remains at proper tension and is properly secured as the servo
moves the controls from stop to stop. Insure that the servo remains secure in its mounting and does not flex its mounting
bracket as it drives the control to its stops. For installations using an arm, insure that as the servo moves the control towards
the end of control travel it does not cause the main control’s torque tube to flex in any way that could cause control system
lockup at the extremes of servo travel. Insure that any “lost motion” in the linkages is eliminated or minimized, in order to
maximize the performance of the autopilot. Lost motion (dead zone) will result in wandering or slow “hunting” behavior in
flight.
The next step in the check-out procedure is to verify that the serial input from the GPS receiver is being properly received and
interpreted. With the aircraft outside of any building, power up the GPS panel-mount receiver and the autopilot. After the GPS
receiver acquires its position, the autopilot will begin to flash the “*” character once per message from the GPS unit showing
that valid position data is available. The display will still show MAG followed by a flashing “*” character, followed by the
present approximate magnetic heading. If no “*” is displayed even after it is known that the GPS unit has a position fix, the
problem must be diagnosed. Possible reasons for such a problem are,
ƒ Pin 25 on the connector is not wired to a source of RS-232 serial data
ƒ The GPS receiver’s baud rate disagrees with that selected within the autopilot
ƒ The GPS receiver’s serial output port has not been properly configured to provide the information
For a DFC-300 system, the next step in the checkout procedure is to verify operation of the yaw damper. Before this test,
remove the yaw damper module from its mounting location (a vertical bulkhead) so that it can be manually tilted. Verify the
direction strap is correctly wired on pins 16 and 17 of J501, the 25-pin yaw damper connector. If the unit is to be mounted on
the rear side of a bulkhead, the strap between pins 16 and 17 of J501 must be absent; if the unit is to be mounted on the front
side, the jumper must be present.
Having verified the strap, manually center the rudder and then engage the yaw damper by pressing the MODE key on the
autopilot programmer. (Any time the autopilot is off; the yaw damper may be toggled on and off using this key, so long as the
aircraft is not flying slower than the preset minimum airspeed). Hold the yaw damper module in the same position it will
occupy when mounted on the bulkhead in an approximately level position that stops the servo rotation. Tilt the module to
simulate the aircraft banking to the right. The yaw damper should respond by commanding the rudder to move towards the
right, and conversely a bank to the left should move the rudder towards the left. If the servo moves in the wrong direction
during this test, double-check the correct jumper setting on pins 16 and 17 and if found to be correct, interchange the wires on
the yaw damper servo connector (pins 4 and 5 of J401) or at the connector on the yaw damper module (pins 12 and 13 of J501).
Re-check the direction after exchanging the wires.