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RV-12iS Garmin G3X - Trim Up or Trim Down Messg w/ Autopilot - Trim & Servo Value Tweak's?

J

jackking123

Well Known Member
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Just did SD-00001 Trim motor Safety Directive. All I had to do was add BUSHING, the tray and motor were in compliance.

Than started started getting the trim up or trim down with autopilot on message. If you manually trim A/P disconnects (as you should).

I did the trim calibration, and I loaded new new G3X Firmware. It is better and now the trim up or trim down only flashes for a moment.

Did NOT update the RV-12iS VFR Avionics w/Rotax 912iS, Autopilot (AFCS) Settings RV-12iS G3XT Autopilot Rev 3. Reading the update it does something to trim. This is the next step.

Does anyone have some tips or tricks to trouble shooting, had similar experience.
 
N8DAV8R said:
I'm not sure which calibration you are referring to, but I recommend first walking through the steps starting on 30-74 before verifying the final setting illustrated on 30-83.

Click to expand...

That is a great Ref, I will review. I will look at all the settings, then consider updating Autopilot (AFCS) Settings RV-12iS G3XT REV 3,

I noticed the clearance of the stabilator and fairing is too tight, slight rubbing. That is getting corrected first. SL SERVICE LETTER 00068 was incorporated which put in permanent spacers for Stabalator brackets, so you don't have to push washers in there. SD-00001 was also done so the trim "rigging" had to change a little.

Trim Calibration where you set Full Up, Neutral and Full Down... It returns or sets 3 voltages.
  1. Contig Mode, Engine & Airframe.
  2. Select Trim Position Input (often named something like GP1 Elevator Trim or Trim). It may display a "Red X".
  3. Select the Calibrate option. You will see specific prompts to calibrate Full Up, Full Down, and Neutral.
1. Calibrate Full Up
  • Press the Full Up (or UP) calibration option on the screen.
  • Use your stick trim hat switch to run the trim motor all the way to the full up position until the motor stops (you will see the raw input voltage change as the motor moves).
  • Note: If the motor stops moving before it reaches the physical limit due to trim runway protection, bump the switch repeatedly until you are absolutely at the maximum physical travel.
  • Once in position, select Store or Done to save the Full Up value.
2. Calibrate Full Down
  • Select the Full Down (or DOWN) calibration option on the screen.
  • Run the trim motor with your stick hat switch to the extreme full down/nose-down position.
  • Once the motor stops at the physical limit, select Store or Done to save the value.
3. Calibrate Neutral
  • Select the Neutral (or CENTER) calibration option on the screen.
  • Run the trim switch until the elevator trim tab aligns perfectly flush (or visually centered) with the elevator surface.
  • Select Store or Done to save the neutral value.
Saving and Testing
  1. Exit the configuration menu and select Save and Reboot to return to normal flight mode.
  2. On your main PFD, verify that the trim indicator moves cleanly from 0% to 100% and displays the neutral/takeoff mark accurately when commanded by your stick.
 
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Trim position calibration has no effect on AFCS operation.

From your description it sounds like you have automatic trim control enabled, but it is not always able to move the trim motor. This is not uncommon if you have a slightly sticky trim motor that needs more voltage to get moving. Typically this involves small adjustments to the "Pitch Auto Trim Minimum Speed" configuration setting, which is described in Table 30-15 in section 30.4.13.2 of the current G3X installation manual (revision AZ).
 
UPDATE:
Took the tail fairing off because there was a slight rub due to min clearance with stabalator. Increased the clearance. Unlikely this was the issue, but needed to be corrected.

The two clevis bolts in the trim / anti-servo tab linkage were a tad tight. Took cotter out, backed up a slot or two. This extra friction was not ideal I am sure.

Last and most I checked the Autopilot settings and recorded them manually (as according to read-me file). LOADED the new REV 3 of Van's autopilot configuration file for the G3X. It is only 1Kb. It changed the Torque and Gain numbers on servo. Servo Torque values were too low, at least from what Van's recommends. I believe this may have been an issue or the issues. Not sure why they were low, may be the original config files had these settings. The reason for REV 3 spacifically states to address nuisance TRM messages while in auto trim.

Have not test flown yet. The weather has been weird, hot, humid, unstable. Think these changes will do the trick.
 
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