Strange throttle/speed behaviour in auto throttle modes

ArduPlane Plane 4.0
1

Hi !
I’m experiencing a very strange thing in Auto throttle modes. The demanded acceleration output from TECS is oscillating between -.6 and +.6 and this causing a very bad throttle pulsing. The interesting thing is is that I see it on three different planes (different sizes, motor configurations), but I don’t see where is the source of this oscillation. Airspeed is solid, throttle RCin does not change. Any ideas before I start poking around in TECS tuning ? (All three planes has default TECS settings, beside the TRIM_)
Setting throttle slew only mask (more or less) the spikes in motor output. So it is not a solution.

image
image1513×398 143 KB

Log file : https://1drv.ms/u/s!AmcHEcCG2JqsjvYaZWbpdIwc1PwOwA?e=1PqDL8

2

I know it is long shoot, but perhaps @tridge could take a quick glimpse on this? I feel really dumb to not able find the cause.

3

For the record it solved:
There is a bug which causing this behavior with radios that tend to have late frames.
[https://github.com/ArduPilot/ardupilot/pull/15743]
I use RFD868 radios with SBUS pass-through on all my planes and it seems that this radio has longer inter frame timing than expected by the autopilot.
Setting THROTTLE_NUDGE zero, solved the issue.
Thanks for Peter Hall to point to the bug (on facebook)!

4

You may have just saved me some tuning. I’m using RFD900x and I’m seeing the throttle pulsing in FBWB. It cleared up in AUTO, or with throttle input below 50%. THROTTLE_NUDGE to 0 is an easy fix. Thanks!