Flap trims reset to 1000 on boot. Why?

My coax built with PixRacer resets SERVO1_TRIM and SERVO2_TRIM to 1000 each time it boots, whatever the previous values are. For this reason I cannot really take off without aggressive counter-action, as the flaps tell the machine to pitch the hell forward and roll the hell to the left.

Note that when it is finally airborne, it catches the control. However, I manage to take off on maybe 25% of occasions, otherwise it crashes and breaks random parts.

Another coax machine, built with Pixhawk, does not have this issue: SERVO1_TRIM and SERVO2_TRIM remain 1500, and it starts as expected. Neither have I seen any problems with a decade-old APM 2.6.

So what may be the configuration culprit I am missing?

1 Like

Resolved. I use a firmware for PixRacer that supports bidirectional D-Shot, and I attempted to configure it to use D-Shot for the motors. Somehow (don’t yet know how exactly) I apparently configured all the channels to be treated as digital ones, which indeed forces trims to be 1000 for normal channels and 1500 for reversible ones (since it is assumed the system does not care for trims).

So, paying attention to the logic employed, I have set SERVO_BLH_3DMASK to 3 (may be 15 to cover first four channels), and now the servos trim to 1500 and the whole system works as expected. Technically, something is still configured incorrectly, but at least I can fly now.


I don’t know how you figured that out MaxBuzz but it’s exactly the problem and solution I needed! Thank you for remembering to come back and post your solution after you figured it out!

We have a open issue for this, just not got to it yet.