@jevermeister: Zum Thema "Motoren bleiben stehen" bin ich grad in den FAQs eines anderen Projekts über etwas gestolpert:

"One motor stops suddenly in a flight

It may occur if your ESC is configured in soft mode.
It is preferable to set the ESCs in MEDIUM or HIGH mode.
A simple test to check this problem:
- hold the Multicopter firmly in your hand
- start the motors and put a little throttle (enough to feel the gyro correction)
- shake it to counter the motor reaction
- if one motor stops, the problem is then related to motor-ESC combination and you probably need to adjust the timing"

...zumindest den teil mit den verschiedenen modi würd ich mal nachvollziehen.