Throttle Offset Issue: 50% Stick Input Reads 57% in Mission Planner (Broken Trim Hardware)

Hardware Radios
1

Hi everyone,

I am writing on behalf of the Lagari UAV Team. We are dealing with a throttle offset issue on our fixed-wing aircraft that is causing non-linear control.

The Main Problem: There is a significant mismatch between our physical stick input and what ArduPlane registers.

  • When we hold the Throttle Stick at exactly 50% (Center), Mission Planner shows ~57% throttle.

  • This offset exists across the whole range, meaning our “Zero” is not zero, and we hit 100% throttle before the stick reaches the top.

The Root Cause (Hardware Failure): We discovered that the physical Throttle Trim slider on our RadioLink AT9S Pro transmitter is mechanically broken.

  • The trim button appears to be stuck in a “High” position and does not respond to clicks.

  • Because of this, our Minimum PWM is stuck at ~1108us instead of the standard 1000us.

  • This explains why the midpoint is shifted high (57% instead of 50%).

Hardware Details:

  • Radio: RadioLink AT9S Pro (2.4GHz system).

  • Receiver: RadioLink R9DS.

My Question: Since I cannot physically repair the trim button right now, I need a software workaround in ArduPlane parameters.

If I manually change RC3_MIN and RC3_TRIM to 1110 (to match the “broken” floor of 1108), will ArduPlane automatically re-map the 0-100% range to fit within the remaining signal (1110us to 2000us)? Or do I need to adjust other parameters to fix this “50% = 57%” offset?

Thank you for your help.

2

You simply need to run the normal radio calibration procedure.

But it might be also a good idea to go through the complete setup documentation, as I think you have never done this before

1 Like
3

I did the radio control calibration and still it didnot fix the issue. It showes the Min as 1108. When i move the stick of the RC to 50% it showes me 1616 in Mission planner which is approximately equal to 57%

4

In Mission planner is th (raw) PWM rate shown received from your rc-system. So if the your transmitter trim is always at maximum so a value of about 1108 could be normal.

Did you run only the calibration as shown at the documentation or you changed any value afterwards manually as ou said in your first post.

Show all your params