Ok, this is an odd problem. Here goes:
I have the pixhawk armed without GPS (solid blue light, APM Planner says "armed").
Pixhawk is plugged into my computer over USB
BEC powering servos (well, one servo at the moment) by it's plugged into the AUX rail.
PPM input through RC IN.
Radio is calibrated and reading fine (when I move the sticks, I see the correct movement in APM Planner).
The Pixhawk says it's giving servo output (I went to the failsafe tab and watched the servo output) and it's moving.
HOWEVER the servo doesn't move. I've tried Ail, Thr, Elev, Rud and none work.
I've reflashed the Pixhawk and that didn't fix the problem. (I'm a bit of a diy dev).
Any ideas on what I can test?
Is is possible that everything works except for the servo output (something blown)?