Twitching on channel

Hi everyone,

I’m in the process of setting up the Pixhawk 2.1 and there is an extreme twitching on SERVO 1 (currently set to aileron).
I’m wondering if it may be a hardware issue with the Pixhawk itself, or some software issue.
I’m running 3.8.1.


  • It happens when in Manual mode and as well as FBWA.

  • Mission Planner radio calibration screen shows correct response to joystick movements and doesn’t show the extreme excursions that are being output. So the signal coming in from the RC system is fine.

  • It only happens when armed.

  • When the button is pressed to disarm it, the servo travels perfectly back to neutral (where it should be).

  • During the moments when it’s in “excursion” position, the RC TX joystick can be used to “fight it” and bring it almost back to neutral.

  • Radio calibration in Mission Planner has been run, so the travels look fine.

  • Voltage being received by servo is 5.27 V, which is fine.

  • RFD900 radio modem is not powered to eliminate it as a source of interference.

  • Swapped servo — same problem.

  • Also tested with motor ESC unpowered and UBEC (for 5V servo rail) unpowered, and instead powering 5V servo rail with lab supply set to 5V — same problem.

Does anyone have any thoughts?


I’ve solved this and thought I’d post it for anyone interested.
By the way, this aircraft is still being set up and hasn’t flown yet, so there are numerous settings that aren’t yet configured.
Here’s what I found:

After reviewing logs, I confirmed that the autopilot was knowingly making the commands causing the twitches, so it wasn’t a hardware fault or interference etc.

Further, in playback, I could see that RTL was activated at all times during the crazy twitching.

Manual was actually selected on the transmitter, so I’m not sure why it was in RTL, but anyway…

And I confirmed now that the same behaviour happens if I select RTL.

Just now, the switch selection of Manual was being obeyed and there was no crazy twitching.

My conclusion: it was caused by it being in RTL mode.

Unknowns are:
— why it was going into RTL
— why RTL would cause such extreme maxed-out movements.

Anyway, things are looking up!


You may need to do a radio calibration as well as a flight modes setting in initial setup, mandatory hardware. I have also noticed it doing crazy things in RTL mode when setting stuff up, it may also be that the GPS is drifting while it is in RTL mode and that is causing the extreme servo movements, its just trying to do its job but with a bad gps signal so its bouncing around.