See video: https://www.youtube.com/watch?v=7byJNPC09FE
My setup: The APM Power Module does not power the motors, just the Pixhawk via the thin cables and it delivers 5V via an UBEC to the PWM output lane so that the OPTO ESCs get voltage. The motors have their own battery pack each (so 6S 4P).
When I connect only via USB, everything seems OK. When I connect the APM Power Module, the red FMU LED goes on, which should indicate some error.
It's the same without USB connection. I have also disconnected the external GPS and the UBEC, so that only the thin cables go to the Pixhawk, nothing else. I still get the red FMU LED.
Oh, and I get very strange reactions from the motors. I have checked the motor order and cabling many times, I also did the calibrations. They don't spin up and down in the right order when I rotate the frame without probpellers. Also the wrong motors accelerate when I give input via the TX. But the cables and motors are guaranteed in the right order. I have also selected X as frame type.
This was the crash at the first flight, now I am trying to debug:
The motors are reacting wrong in a diagonal fashion. I couldn't correct it by switching the motor cables. They are in the right order, checked about 10 times.