F

Fredrik

Active Member
This is a shout for some input from the other side of the pond:)

Yesterday I was testing the autopilot (GX) in my G3X system for the first time.
I took off and engaged the AP by cws button in a moderate climb. Then I got "TRIM DOWN" annunciation on the PFD. I started to trim down with short trim inputs and after some more trim down the AP disengaged and I went in a steep dive. After a couple of tries I decided to try trim up instead when I got "TRIM DOWN" message (which is logical in a climb). The annunciation stopped and AP climb was successful.

The trim is working correctly and is not reversed, the trim indicator on the PFD is also correct. My trim servos are connected through VP-X sport and not directly to G3X. The TruTrak GX servos are also not reversed (would be a bit unpleasant to fly).

I don't really known if this is a Garmin, TruTrak or VerticalPower support issue so I ask here first if anyone seen this before.

Thanks for any input,
Fredrik
 
If you are using a TT GX Pilot AP, the "Trim UP/DWN" indications come from the GX Pilot.

Did your control head also display a need for trim?

If so which way did it tell you to trim?
 
Ok, so it's the TruTrak GX Pilot instrument that initiate this message?
Sorry, I didn't notice what direction the TT instrument was showing. Can it be opposite to what it is telling the PFD?
There isn't much of configuration to do in the TT and I can't find any proper configuration to alter in the G3X system.
 
Hello Fredrik,

Brian is correct that the need for trim up/down is determined by the TruTrak GX Pilot and provided to the G3X system over the RS-232 serial connection and has nothing to do with the VP-X system or anything else.

Have you tried to trim the plane for straight and level flight and then engage the autopilot in altitude hold and see if it flys this fine?

We are still wondering if the pitch servo direction might be reversed and you are over-powering it with up trim in the climb, but you sound pretty confident that this isn't the case. Telling us a little more about how the autopilot is working in other modes could help us diagnose.

Please check that servo direction is correct on the ground before flying again.

Thanks,
Steve
 
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Hello Steve, and thank You for Your quick support on Sunday, regarding servo-config.

I have tested the AP in stand alone mode with altitude hold and that worked without any issues (trimmed for level flight).

Yesterday, after I figured out to trim opposite to annunciation, I flew a flight plan track for 130 nm, without any AP issues (except for some slow altitude oscillations (+-20ft) also flew descent with AP VS and no issues.
 
Hello Fredrik,

You are very welcome.

We retested our G3X to GX Pilot interface this morning to make sure the trim needed annunciations on the PFD still match those on the GX Pilot control head and everything looked good.

Would you mind checking to see if the G3X annunciations match the GX Pilot control head indications for your system?

Thanks,
Steve
 
Ok!

I'll go out to the airport tomorrow. Is there a good way to do a static test for this (not airborne)? The airport charges almost $50 in landing fee :mad:
 
Fredrik,

$50 to land! Ouch!

You should be able to engage the autopilot on the ground in Pitch and Roll modes, then push on the stick in one direction until the autopilot senses that it needs trim and posts the indication.

Let us know if you have additional questions. If useful, you might take a video or pictures.

Thanks,
Steve
 
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Fredrik,

My apologies for not seeing this sooner. There is a definite way you can have your servo direction be correct but your trim direction be incorrect. There are two ways to reverse the direction of travel of your pitch servo, either by swapping wires (pins 4 and 5 at the servo) or by utilizing the pitch reversal jumper on the autopilot controller. Using the jumper reverses both the direction of the travel and the trim annunciation direction. Swapping the pins reverses only the direction of travel but will leave the trim annunciation in the original orientation.
 
Lucas, Steve and Brian,

Thanks for your knowledgeable input! Problem solved.
The servo pins 4 and 5 where switched and I had a jumper at controller pins 1 and 2, so the pitch servo was actually double reversed (working in correct direction) and trim indication where single reversed. I switched controller pins 8 and 9 (easier to access) and removed jumper cable.

This mistake was from back in 2008 when I installed the first AP, TT DigiFlight II. That one didn't have trim annunciation. Now, when I rebuilt my panel with the TT GX I used the old servo harness with the pin mix up.

Now back to test flying.

How about the mild altitude oscillations (porpoise?)? Is that curable? My DigiFlight II was rock solid in default configuration.

Thanks!
Fredrik
 
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