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G3X Manual Trimming not functinal if autopilot is powered

Ezburton

Well Known Member
Patron
All,
I have a dual G3X Touch system with pitch and roll autopilot servos and a GMC305 autopilot control panel. I've performed the setup procedures when I first powered up the panel and everything worked fine. Subsequent to that, (almost) every time the autopilot is powered (but not connected) I cannot use the manual trim. If I pull the CB to the autopilot, the trim works fine. Right now, I pull the AP breaker before I fly (so I can trim) then set the breaker and engage the AP and it trims fine on its own.

My setup includes a relay board which toggles the polarity of the manual trim signal, which passes through the pitch servo, to a relay which then provides power to the trim actuator. The added relay was needed due to the higher current (greater than 1amp) which the Garmin servo can provide for trimming.

We thought it was a servo problem and replaced that under warranty. It worked fine when the tech left, but without touching anything else, it stopped working before the end of the day. When I got the tech on the phone a few weeks later to help debug, it worked fine! Next weekend it didn't work and hasn't worked since.

The fact that the trim works manually (every time) when the AP is not powered indicates that the wiring is good. When the AP is powered and engaged the servo controls the trim actuator fine. The AP disconnects when the manual trim switch is pressed. So that seems to be wired correctly as well. I'm stumped/frustrated about why I can't manually trim with the AP powered but not engaged?

Anyone had a similar issue or have any idea what might be causing this?

Thanks,

Don
 
All,
I have a dual G3X Touch system with pitch and roll autopilot servos and a GMC305 autopilot control panel. I've performed the setup procedures when I first powered up the panel and everything worked fine. Subsequent to that, (almost) every time the autopilot is powered (but not connected) I cannot use the manual trim. If I pull the CB to the autopilot, the trim works fine. Right now, I pull the AP breaker before I fly (so I can trim) then set the breaker and engage the AP and it trims fine on its own.

My setup includes a relay board which toggles the polarity of the manual trim signal, which passes through the pitch servo, to a relay which then provides power to the trim actuator. The added relay was needed due to the higher current (greater than 1amp) which the Garmin servo can provide for trimming.

We thought it was a servo problem and replaced that under warranty. It worked fine when the tech left, but without touching anything else, it stopped working before the end of the day. When I got the tech on the phone a few weeks later to help debug, it worked fine! Next weekend it didn't work and hasn't worked since.

The fact that the trim works manually (every time) when the AP is not powered indicates that the wiring is good. When the AP is powered and engaged the servo controls the trim actuator fine. The AP disconnects when the manual trim switch is pressed. So that seems to be wired correctly as well. I'm stumped/frustrated about why I can't manually trim with the AP powered but not engaged?

Anyone had a similar issue or have any idea what might be causing this?

Thanks,

Don

I'm only on my first cup of coffee.... but I would suspect the 'boost' relay which I assume is now being controlled by the PWM modulation output of the servo doesn't like that signal. When the AP is on the output from the servo is a PWM signal, when the AP is off the servo act as a pass thru for the DC trim control.

I understand TCW makes a box for just this purpose which some of the Glasair guys use.
 
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I've seen something like this and have been wanting to talk to the G3X guys about it. I'm still building, so I haven't engaged the AP yet. I've found that trim works fine with the AP disengaged on the ground, but it doesn't if I engage CWS (I have a AP disconnect switch on the panel which engages CWS).

G3Xperts: Enlighten us!
 
All,
I have a dual G3X Touch system with pitch and roll autopilot servos and a GMC305 autopilot control panel. I've performed the setup procedures when I first powered up the panel and everything worked fine. Subsequent to that, (almost) every time the autopilot is powered (but not connected) I cannot use the manual trim. If I pull the CB to the autopilot, the trim works fine. Right now, I pull the AP breaker before I fly (so I can trim) then set the breaker and engage the AP and it trims fine on its own.

My setup includes a relay board which toggles the polarity of the manual trim signal, which passes through the pitch servo, to a relay which then provides power to the trim actuator. The added relay was needed due to the higher current (greater than 1amp) which the Garmin servo can provide for trimming.

The fact that the trim works manually (every time) when the AP is not powered indicates that the wiring is good. When the AP is powered and engaged the servo controls the trim actuator fine. The AP disconnects when the manual trim switch is pressed. So that seems to be wired correctly as well. I'm stumped/frustrated about why I can't manually trim with the AP powered but not engaged?

Anyone had a similar issue or have any idea what might be causing this?

Thanks,

Don

Just to add to what Walt said, I have installed the TCW Servo Boosters in a Glasair III and a Velocity XL/RG, both with Garmin panels and servos and both have worked just fine. Like you said, the servo booster goes between pins 13 and 14 of the GSA 28s to the trim actuators (both of these airplanes use an actuator that draws up to 5 amps or so). You'll probably need to call Bob Newman at TCW because I don't think he has these up on his web site yet.

In both instances, we used one of our relay boards to reverse polarity of the power to pins 11 and 12 of the GSA 28 servos, both pitch and roll. As you point out, the GSA 28s will only drive about an amp or less to the trim motors, which is fine for the Ray Allen trim motors, but for folks like yourself who need to use the larger trim actuators, Bob developed these servo boosters. They work really well.
 
Don,

As has been pointed out earlier in the thread, a standard relay will likely not function properly with the PWM input. You mention that auto-trim is working with the autopilot engaged. Auto-trim also uses the PWM output from the servo and I would expect this to not work, or at least to work inconsistently.

The TCW Servo Booster is specifically designed for the application of taking the PWM output from the primary servo and providing an output for a trim servo which requires greater than 1 amp. You can reference the interconnect to the G3X system in the installation manual (190-01119-01 rev AG) on Figure 27-1.9.

Without a product designed to take a PWM input, your results may vary.

Thanks,
Levi
 
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Sounds like this is my issue. I'll get with my avionics guy and try to get this resolved.

Thanks all for the input... that's why I pay my dues! I'll reply back with what I find out to close out the thread.

Don
 
So I checked this out with my Avionics guy and he agreed that the relay supplied was not going to work (consistently). We purchased a TCW unit and I installed a few weeks back. Now the trim works when the SP is powered up, but now I have a new problem...

I get the red TRIM annunciation on the PFD (at all times) and the trim test boxes do not appear on either the pitch trim or the roll trim (note the roll trim had NO changes made to it). First question is what triggers the TRIM failure annunciation? If it didn't know I was trying to use autotrim, then I assume I wouldn't be getting the annunciation.

I think the autotrim configuration is set correctly. I scanned through all of the menus looking for some lost setting and didn?t find anything:

On the system info page, there are 2 unchecked boxes, one for RTRIM and the other for PTRIM. I think this indicates that something isn?t right, despite the Auto trim being enabled for pitch and roll and the trim pass through working and indicating correctly in the System Info ? Autopilot Servo Info page. Before the swap, I did have the trim test boxes and they worked as in the install instructions.

I suspect there is something not right with this new relay setup since it is the only thing that has changed, but why would the roll autotrim have died as well (its a MAC trim servo which doesn't require the TCW box)?

I also did the recent software updates to 7.0.

Any ideas or suggestions would be appreciated.
Thanks,
 
Don,

With software version 7.00, we added the ability to use a GSA 28 as a pitch trim servo. The GSA 28 is not really applicable to the RV series as a Pitch Trim motor because there must be a manual trim system for the GSA 28 to tie into.

If you tell the autopilot you have a pitch trim servo, it will look for a GSA 28 which is not there in your case.

Go into configuration mode on the LRU page. In the Autopilot section disable off the "pitch trim servo" as this is looking for a GSA 28 as a pitch trim motor. I believe everything will work properly for you after you do this.

Thanks,
Levi Self
 
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Thanks Levi,

Not sure we are on the same page though. I have two GSA28 servos, one Ray Allen actuator for roll trim and one Warner linear actuator for pitch trim.

So is what you are saying still correct? We can talk off line if you prefer. ezburton at yahoo dot com

Thanks,
 
Don,

I was a bit too fast with my first response and said "pitch servo" when I meant, "pitch trim servo". I have edited my post above. Please read and follow the guidance in that post to fix your issue. If you have questions, we can help you at [email protected]

Thanks,
Levi
 
Interesting thread. I have my electric trim (2-axis) system running through the VP-X Pro, which has a "runaway trim" disable function. Inflight with the AP servos powered, the autotrim system keeps the aircraft in proper trim, whether or not the AP is actively steering the aircraft. I don't believe that I can alter the trim manually when the AP servos are powered. My before landing procedure is to depower the AP servos, which allows me to dial in more nose up trim on final than the autotrim usually applies (if the AP servos were powered) - just my preference.
 
Don,

I had a Trutrak AP with autotrim module (which I assume is similar in functionality to the Garmin system). When you engage the AP, it uses the autotrim module to maintain proper trim and specifically turns off manual input which is not needed.

AP on = autotrim
AP off = manual trim

So if you have auto trim that may be the "culprit."
 
Interesting thread. I have my electric trim (2-axis) system running through the VP-X Pro, which has a "runaway trim" disable function. Inflight with the AP servos powered, the autotrim system keeps the aircraft in proper trim, whether or not the AP is actively steering the aircraft. I don't believe that I can alter the trim manually when the AP servos are powered. My before landing procedure is to depower the AP servos, which allows me to dial in more nose up trim on final than the autotrim usually applies (if the AP servos were powered) - just my preference.

That operation seem really weird to me, on the standard Garmin system:

The auto trim (no VPX) auto trims only when the AP is engaged.
If the AP is engaged and you manually trim the AP disconnects.
When the AP is not engaged the manual trim works normally.
Trim speed is based on airspeed and is always active when the servos are powered.
 
Do you really want electronic flight control inputs when you're near the ground like in takeoff or landing where the good 'ol "meat servo" usually does a very good job?

I like the way my G3X disconnects the AP whenever I manually trigger the electric pitch trim. That's the same way it works on every higher performance plane I've flown like King Airs, corporate jets, large airliner turboprops and regional jets.
 
First off, I found the settings in the G3X and disabled the trim servo functionality, which it seems disables the GSA28 from being the trim servo and enables the trim actuators I have installed. This cleared the red TRIM fail annunciation. I didn't have much time to test the functionality of the trim due to having a short flight with lots of traffic in the area.

When it worked intermittently, it was nice to have the AP trim while flying. It did throw up an annunciation when it was doing it (not sure I would have made it a caution... cyan or white would have been better IMO since it is a normal function). When I disconnected the autopilot the plane was trimmed just fine like the right seater just transferred controls to me.

WRT electronic inputs near the ground, I would use the AP to fly an approach to the missed approach point and perform the go-around. Given the speed changes, why would you not let it trim?

Thanks for helping me get this straightened out. The lesson learned here was to not change software in the middle of troubleshooting the problem. This was the last problem to solve with the glass upgrade.
 
All,
I have a dual G3X Touch system with pitch and roll autopilot servos and a GMC305 autopilot control panel. I've performed the setup procedures when I first powered up the panel and everything worked fine. Subsequent to that, (almost) every time the autopilot is powered (but not connected) I cannot use the manual trim. If I pull the CB to the autopilot, the trim works fine. Right now, I pull the AP breaker before I fly (so I can trim) then set the breaker and engage the AP and it trims fine on its own.

My setup includes a relay board which toggles the polarity of the manual trim signal, which passes through the pitch servo, to a relay which then provides power to the trim actuator. The added relay was needed due to the higher current (greater than 1amp) which the Garmin servo can provide for trimming.

We thought it was a servo problem and replaced that under warranty. It worked fine when the tech left, but without touching anything else, it stopped working before the end of the day. When I got the tech on the phone a few weeks later to help debug, it worked fine! Next weekend it didn't work and hasn't worked since.

The fact that the trim works manually (every time) when the AP is not powered indicates that the wiring is good. When the AP is powered and engaged the servo controls the trim actuator fine. The AP disconnects when the manual trim switch is pressed. So that seems to be wired correctly as well. I'm stumped/frustrated about why I can't manually trim with the AP powered but not engaged?

Anyone had a similar issue or have any idea what might be causing this?

Thanks,

Don

Updating this old thread in hopes it may help someone else. I own a 2019 RV-12iS (E-LSA) with a G3X Touch, GMC 307 and GSA28 pitch/roll servos. The pitch trim servo is a Ray Allen. Pitch trim was enabled in the config.

Since inception in 2019 when I took delivery of the plane with 17 hours on it, intermittently, when the autopilot was engaged, I would get a pitch up that could at times be severe. The only way to correct it was to pull the autopilot breaker, or power off the GMC307.

Even then, the trim up/down buttons on my stick were unresponsive at times unless I rocked the trim up/down a couple times. The issue was severe enough for me to quit using the autopilot 9 months ago. This never occurred at the time the autopilot was powered on. Rather, it was some time after that. When the autopilot was engaged, attempting to manually trim with the stick controls disconnected the autopilot.

After upgrading the G3X Touch firmware from V9.0 to V9.13 (lots of LRU updates, too), the issue seems resolved. I also disabled pitch trim in the config. Manual (electric) trim now works when the servos are engaged, and I've gotten "trim down" annunciations a couple times, which never happened previously.

So resolution was one or more of the following:

  1. Needing the fixes in the V9.13 update,
  2. Disabling pitch trim,
  3. Not putting any pressure on the stick when servos are engaged. In testing post update, I was careful to only guard the stick. The G3X Touch Pilot Manual has warnings about using any pressure on the stick when the servos are engaged - that it can cause runaway trim.
 
G3X Touch Autotrim

Updating this old thread in hopes it may help someone else. I own a 2019 RV-12iS (E-LSA) with a G3X Touch, GMC 307 and GSA28 pitch/roll servos. The pitch trim servo is a Ray Allen. Pitch trim was enabled in the config.

Since inception in 2019 when I took delivery of the plane with 17 hours on it, intermittently, when the autopilot was engaged, I would get a pitch up that could at times be severe. The only way to correct it was to pull the autopilot breaker, or power off the GMC307.

Even then, the trim up/down buttons on my stick were unresponsive at times unless I rocked the trim up/down a couple times. The issue was severe enough for me to quit using the autopilot 9 months ago. This never occurred at the time the autopilot was powered on. Rather, it was some time after that. When the autopilot was engaged, attempting to manually trim with the stick controls disconnected the autopilot.

After upgrading the G3X Touch firmware from V9.0 to V9.13 (lots of LRU updates, too), the issue seems resolved. I also disabled pitch trim in the config. Manual (electric) trim now works when the servos are engaged, and I've gotten "trim down" annunciations a couple times, which never happened previously.

So resolution was one or more of the following:

  1. Needing the fixes in the V9.13 update,
  2. Disabling pitch trim,
  3. Not putting any pressure on the stick when servos are engaged. In testing post update, I was careful to only guard the stick. The G3X Touch Pilot Manual has warnings about using any pressure on the stick when the servos are engaged - that it can cause runaway trim.

It sounds like you disabled Auto-trim. When Auto-trim is enabled, it is expected that manual trim disconnects the autopilot if the autopilot is engaged.

Have you ever sent us an email with a flight datalog for this problem? I just took and a look and did not see one. If you would like to send one over I would be happy to take a look at it for you.

Thanks,

Justin
 
It sounds like you disabled Auto-trim. When Auto-trim is enabled, it is expected that manual trim disconnects the autopilot if the autopilot is engaged.

Have you ever sent us an email with a flight datalog for this problem? I just took and a look and did not see one. If you would like to send one over I would be happy to take a look at it for you.

Thanks,

Justin

Nope, it was pitch trim that I disabled. Per another old thread here, that is to be enabled only if you have a GSA28 as the pitch trim servo.

Well, now I'm ticked at myself. My emails to you were sent to [email protected], which is wrong. Have resent.
 
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