Elevon Servos have very small range and act "jumpy"

I’m using a matek F765 for a delta wing, FT1117 servos for elevons and using a computer joystick with mission planner to send RC messages.
I set the two servo outputs to eleven left/right, set min/max to 900/2100 (taken from servo specification), modify map to match the controller controls X/Y to pitch/roll respectively, and go through the radio calibration process.
Testing in manual mode, I am getting a very small travel range, around 20 degrees, even though the servo itself is specified for 120 degrees. When my stick is idle, one defaults to 1400 and the other to 1600 (I’d expect them to stay at 1500 when neutral? same trim, min and max settings for both), and the deflection applied to any of the two when I move the stick is small, maybe 100-200. Verified that the RC input is at max, while the servo output is close to the neutral point.
When setting them to Elevators or RCin, I get a larger throw, close to 80 degrees. It’s an improvement but still misses around 40 degrees of the nominal range.
On top of having a very small range, the servo movement is not smooth at all, exhibiting erratic jumps when sweeping the control range slowly. While it can get to the max position fine, it doesn’t look like it offers a viable resolution for it to be accurate in-flight.

I’ve gone through the servo documentation and can’t really figure it out. What am I missing?

Ohhhhh this is EXACTLY the problem I’m going through. If anyone can chime in, it would be much appreciated.

(Hopefully Spiros my msg sends this to the top and get seen to save the day :slight_smile: )

Spiros, change your mixing gain from a default of 0.5 to 1.0 (or somewhere in between). Resolution should improve too.

After a lot of fiddling around with various settings, I’ve identified the problems:

  1. “Jumpy” behaviour is just low RC update rate from mission planner. I suspect the radio settings I use are the bottleneck for that, not sure if I want to change them since FBWA mode is smooth anyway.

  2. I tried the whole radio calibration and servo calibration process again, and eventually it worked. My impression is that my instance of mission planner didn’t correctly update the servo min/max values, causing the problem.