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.
I am confused. Did you intentionally stop your motors in flight?
Was this to test an added safety circuit or some other failsafe/rescue mechanism?
Or are you stating that while flying, two of your motors stopped?
It is unclear if you are reporting an induced result or a system failure?
Please clarify. If a system failure, post your *.tlog file from the APM so that we may attempt to augur out the cause...perhaps.
It is sad to see damage but let us hope you can learn what went wrong.
If you stop the motors mid-flight you're rolling the dice as to whether they will start up again.
As you say, they reverse in freefall and the ESCs can't get back in sync to move them the right way again, they're not designed to be able to handle that case.
Sounds like logic for inverted descents needs to be added.
I too have had a motor stall on me during rapid descent. They've always restarted though when you give it full throttle.
Try use plastic screws to mount your motors - unlikely you would have broken them as they would have snapped. Saved me many many motors.
There should be a standard "motor on and slow spin" as soon as the APM is armed to avoid a total motor shutdown in mid air. I think mikrokopter offers that.
Actually, we should have something like slow motor spin after some fixed alt. above ground.
Because stabilize is the only mode they can be stopped in, if flying loiter, full down mens descend fast, and if mode is confused, or pilot just want to descend faster, could stop motors by accident.
I wanted to test is there was a reliable recovery from such situation.
exaclty what I am trying to motivate people to vote for.
strangely your motor cables look like they were cut by the props.
Weren't they secured?
where can we vote for?
I like the idea of once the APM knows you are in the air it should prevent a full zero throttle in stabilize mode. If you really want to shut them off then go to ACRO. Full off shouldn't be allowed in stabilize like it's not in other modes like alt hold. But it should be able to descend faster than a full down in alt hold. Just keep them spinning at the minimum speed that prevents them from stopping.