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Strange throttle/speed behaviour in auto throttle modes

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.


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

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.

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)!

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!

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