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G3X / GEA 24 Non Linear Pitch Trim Voltage

walter

Well Known Member
I've been communicating with the G3xperts on this but I want to run this by the community as well. Looking for ideas and leads to help trace an issue.

On my 8A the 5 Volt elevator pitch trim indicator voltage is non linear during calibration. This makes it difficult to find neutral pitch trim using the trim indication on the G3X. You have to use eyeballs instead. I've recalibrated it at least 4 times with the same results.

IMG_4021D.jpg

Fortunately, roll Trim Voltage is linear and working as expected. Both trim motors are working as expected throughout their travel.

Pitch trim motor indicator voltage (Ray Allen) checked out as linear throughout its movement on the bench.

We've swapped out the GEA-24 and that is not the problem.

Maybe somebody has seen this before and has a fix...Next attempt to fix will be to take everything apart. So hard to take it down - it's too much fun to fly.

Other info: Pitch trim on the stick with coolie hat (Infinity), GMC 305 autopilot (auto pitch trim turned off) and roll and trim relays installed.
 
I've been communicating with the G3xperts on this but I want to run this by the community as well. Looking for ideas and leads to help trace an issue.

On my 8A the 5 Volt elevator pitch trim indicator voltage is non linear during calibration. This makes it difficult to find neutral pitch trim using the trim indication on the G3X. You have to use eyeballs instead. I've recalibrated it at least 4 times with the same results.

View attachment 11465

Fortunately, roll Trim Voltage is linear and working as expected. Both trim motors are working as expected throughout their travel.

Pitch trim motor indicator voltage (Ray Allen) checked out as linear throughout its movement on the bench.

We've swapped out the GEA-24 and that is not the problem.

Maybe somebody has seen this before and has a fix...Next attempt to fix will be to take everything apart. So hard to take it down - it's too much fun to fly.

Other info: Pitch trim on the stick with coolie hat (Infinity), GMC 305 autopilot (auto pitch trim turned off) and roll and trim relays installed.


Check your trim indicator wiring (wh/bl, wh/gr, wh/or wires)...
 
Walter,

It looks like you are only using about half of the input range. I'm going to take a wild guess that one of the connections is not good to the trim servo. The measurement circuit in the servo may have current paths that we are unaware of such as an internal pulldown or a divider network that would result in partial operation.
 
I've been communicating with the G3xperts on this but I want to run this by the community as well. Looking for ideas and leads to help trace an issue.

On my 8A the 5 Volt elevator pitch trim indicator voltage is non linear during calibration. This makes it difficult to find neutral pitch trim using the trim indication on the G3X. You have to use eyeballs instead. I've recalibrated it at least 4 times with the same results.

View attachment 11465

Fortunately, roll Trim Voltage is linear and working as expected. Both trim motors are working as expected throughout their travel.

Pitch trim motor indicator voltage (Ray Allen) checked out as linear throughout its movement on the bench.

We've swapped out the GEA-24 and that is not the problem.

Maybe somebody has seen this before and has a fix...Next attempt to fix will be to take everything apart. So hard to take it down - it's too much fun to fly.

Other info: Pitch trim on the stick with coolie hat (Infinity), GMC 305 autopilot (auto pitch trim turned off) and roll and trim relays installed.

Do the calibration again. system should show about .5 volts or less at one extreme and around 4.5 volts or greater at the other. If you are substantially off from those, you either have a wiring issue or your trim motor has some type of internal issue with the potentiometer. From the look of your chart, I am guessing a bad pot inside the motor. It is a std linear pot and the non-linear behavior points to a bad pot.

I take that back. Just delete the Neutral position from the calibration and all will be fine. You only calibrate the two extremes with no neutral, assuming you want a linear reading. You use the alert funcionality to set a hash mark at the point you want for TO trim position, not a neutral calibration point. You have made the reading non-linear by putting a highly skewed neutal position. The jog in the line is due to where you put the neutral position. If you must have a neutral set point, split the voltage difference between the extremes and put it there to be linear. If your neutral calibration truly matched the physical neutral position, you may have the mechanical linkage on the trim motor messed up.

Larry
 
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