During tesing of motor-off recovery at safe altitude (60meters), the quad fell stright down, - propellers were spinning backwards, and motors stalled, not being able to turn in right direction.
At much too low altitude, the quad rolled, making 2 of the motors able to spin up, but it was too late then.
-motors should be kept on at all time when the APM is armed, stopping motors is asking for dangerous situations..
I created a issue here: https://github.com/diydrones/ardupilot/issues/431
Feel free to support it.
"both", not "but" .
I feel this is a problem with ESCs and should be solved at the source. We need ESCs that are specially designed for quads and can spin up even if they are rotating in reverse after a situation such as you describe. I think it would be dangerous if the props kept rotating in idle as there would be no quick way to do a quick shutdown in an emergency situation. It would also be nice if the ESCs had a PID controller to keep prop RPMs proportional to input signal and if they could report their status back to the APM if for whatever reason they couldn't maintain desired RPM. I know AutoQuad is working on an ESC designed especially for quads... I wonder if they have any solutions for this problem.