I know that it is taken as common knowledge that a hexacopter with a single motor failure cannot be flown beyond a controlled crash landing, but this is just plain wrong with our ArduPilot Mega hardware and if we can't do it, it is because of inadequate software.
I have a KK X525 quadcopter which I have flown very successfully for some time with the APM2.
One ESC on it is now progressively failing, continuously reducing power to it's motor after about 2 minutes flight, but all you notice immediately is the need to feed in a little more throttle and eventually it starts descending even at high throttle.
Once it touches the ground you need to switch out of any auto mode to prevent it flipping over (usually too late).
But the moral is that even with one motor failing it tries to maintain level and flight is still controllable.
On a hex if one motor fails all you should have to do is shut off the opposite motor and it should still be completely controllable as long as you have sufficient thrust in the remaining 4 engines to hover the copter.
Auto shutdown of an opposite motor could be handled entirely in software on the APM and control should be fully maintained. as you still have 2 motors turning each way and the lefit points are still symmetrical.
No spinning, no loss of control, no nothing.
If the Arducopter doesn't do this it should and I would definitely like to know what you think.
This could be a tremendous safety and long term cost advantage for a hex and not require an Octo as previously thought.