GTN 650 Configuration for TruTrak Autopilot

I?m having a heck of a time getting my Trutrak VSGV to work.

I am not absolutely certain that I have made the proper ARINC settings on the GTN. I feel that I have the correct RS232 setting.

What confuses me is the ARINC ?A? & ARINC ?B?. On the GTN ARINC configuration screen, there is no reference to ?A? or ?B?. I see ?ARINC 429 in 1? & ?ARINC 429 in 2? along with ?ARINC 429 out 1? & ?ARINC 429 out 2?.
Does the 1 & 2 refer to A & B or port number?
When I look at the pin-out list in the GTN install manual, I see reference to ARINC ?A? & ?B?.

I have tried a couple of different settings but get the same result: a right nose-down bank carnival ride.
I do get the A/P ?GPS OK? * a flashing asterisk; also get the TRK with the correct heading and a ?+? when a flight plan is entered. I have NEVER seen ?GPSS? show up on the A/P.

The three wires going from the GTN to A/P have continuity & go to the correct pinouts as far as I know.
The A/P has been back to Trutrack & Zack the tech guy says it?s ?ok?.
Also re-checked wiring to servos. All OK.

Any insight to my problem would be most appreciated.

Sam

PS
I recently emailed the avionics supplier & kindly asked to be ?walked-through? the configuration screens. I was told to refer to the (convoluted) configuration sheet that was provided and that was ?all that there is to do?. Some service after dropping $12k+ on this place.
I only regret that I didn?t buy my avionics stack from Walt or Stein, or someone that has presence on the forum. If you?re an avionics novice such as I, don?t be suckered into low prices.

Arinc uses a dedicated return line rather than a common ground. So arinc #1 is a pair of wires, arinc 1A and arinc 1B.

Bob
Is the "return line" considered an output?
Thanks
Sam

You want arinc out from the GTN, in(to) the autopilot. Each arinc is a pair of wires, A and B.
So connect the GTN arinc 1A out to the TT arinc 1A in. Connect the GTN arinc 1B out to the TT arinc 1B in.
You could also use ARINC 2 instead of 1.

You can get some noise immunity just by twisting the A and B wires together. Better still is to use 2 conductor-inside a shield cable. Connect the shield to ground.

Ok, Thanks. I'm pretty sure everything is wired correctly. I'm really just trying to wrap my head around the GTN config screen settings.

RE: TruTrak Autopilot

Reading the description of the symptoms of your autopilot behaviour, I don't think the GTN 650 ARINC 429 wiring or configuration is your problem. When you get a wild ride when engaging the AP in flight, it is more likely the commands from the TruTrak controller to the servos are incorrect.

The A/P ?GPS OK message just indicates that the TruTrak is receiving valid RS-232 data from the GTN650. The RS-232 GPS data is all that the TruTrak AP needs for basic autopilot functions, i.e. track, follow a GPS flight plan, vertical climbs

Question: Have you performed the basic ground checkout that is described in the TruTrak Installation Manual for your TruTrak model AP. You can download the manual from the TruTrak website. The ground check out will confirm that the servos command left and right turns and climb/descents in the correct direction. For the Digiflight II series autopilots, reversal of the pitch servo rotation is via a jumper installed between pins 1 and 2 of the controller connector. Reversal of the roll servo rotation is by swapping pins 4 and 5 at the servo.

If it works correctly on the ground you won't get a wild ride when it you engage in flight.

With regard to the ARINC 429 configuration, the GTN-650 needs to be set for low speed. If your GTN-650 is incorrectly set for high speed, the TruTrak will behave strangely, at least that is what I experienced with a TruTrak Vizion 385.

Power Up?

Sam,

Are you leaving the airplane stationary when you power up the TT autopilot?

I haven't flown one in quite a while but I remember that the Vizion had about a 20 second boot-up time when you power it up. If you move the airplane while this is happening the AP gyros won't be initialized correctly and you can get the wild-ride behavior you described when you engage the AP.

There is also a Gyro Set function that is part of the installation procedure and that calibrates the gyros. The manual will cover how to redo that calibration as well.

Doesn't sound like a wiring problem so I would get the AP working just following GPS (RS232) which you already confirmed is connecting properly and then track down the ARINC/GPSS issue if there is one.


Good Luck,
Andy

Isaac said:

Question: Have you performed the basic ground checkout that is described in the TruTrak Installation Manual for your TruTrak model AP. You can download the manual from the TruTrak website. The ground check out will confirm that the servos command left and right turns and climb/descents in the correct direction. If it works correctly on the ground you won't get a wild ride when it you engage in flight.

With regard to the ARINC 429 configuration, the GTN-650 needs to be set for low speed. If your GTN-650 is incorrectly set for high speed, the TruTrak will behave strangely, at least that is what I experienced with a TruTrak Vizion 385.

Click to expand...

Isaac,

Yes, I have done the ground check. Everything moves in the correct direction. HOWEVER, when I engage the A/P, even on the ground, the stick moves right about one "step" about every two seconds and one "step" forward about every three seconds. I can rotate the encoder knob CCW & move the stick left, CW and the stick moves right. Pushing ALT button, CW moves stick back; CCW, stick moves forward. Also, the control wheel steering works as it should (releases the servos) and displays "CWS" on the screen when I depress the button I have on the stick.

Also, I'm aware of the A/P ARINC low speed requirement and believe I have it set correctly.

I'm currently down for a condition inspection and will dig into it again in a few days. Sorta running out of ideas at this point.
I appreciate you help with my problem

RE: TruTrak

Sam,
The ground check results confirm that the controller to servo's are wired correctly. The ratchety movement of the control stick is due to the fact that the TruTrak pitch and roll servo's are stepper motor's, so they move in distinct little steps.

In your original post, you said that engaging the autopilot resulted in "a right nose-down bank carnival ride". Does that occur in flight or just on ground?

If it is just what you observe on the ground when you engage the AP, it is basically normal behavior because the autopilot controller is expecting the aircraft to move in the direction it is commanding. On the ground, the aircraft can't move, so any small error in pitch or roll attitude or rate will cause the autopilot controller to command the airplanes flight controls in the direction to make the error go to zero. Because the airplane doesn't move the autopilot will keep commanding and commanding and commanding more and more until the airplanes control surfaces hit the stops.

Another operational consideration is that when the airplane is going slow the autopilot (or pilot) must move the flight controls in larger amounts to control the aircraft. At high speed,s only small movements of the control surfaces are required to control the aircraft. When you are stationary on the ground, the autopilots internal gains are at there highest settings because airspeed is zero. So you will observe rapid and large movements of the control stick when engaging the AP on the ground.

Hopefully, the above is helpful information and isn't boring you with stuff you already knew.

You mentioned that you have confirmed that the wiring between the GTN650 ARINC 429 Tx outputs to the TruTrak inputs is correct. The pin designated GPS ARINC Out 'A' on the GTN needs to be connected to the pin designated ARINC 'A' on the TruTrak and the same for the 'B" pins. Have you checked to make sure that you don't have a short between the two Arinc pins or that one of the pins is somehow grounded or shorted to the the shield braid?

If valid ARINC 429 steering signals are being received by the TruTrak from the GTN, pressing the MODE button on the TruTrak controller should result in going directly into GPSS mode. So if that isn't occuring you need to figure out what is wrong with the Arinc data (which is where you were headed in the first place