[drdaeman]

Just curious. Are there RC multirotors that employ some other emergency measures than GPS-based navigation in case of lost connectivity, but can also survive fairly severe power, rotor or engine failures?

Judging from YouTube videos, autorotation doesn't seem to cut it - it's still falling too fast, but maybe something like deploying an emergency parachute - if altitude allows for it, or maybe (not sure if that's a sane thought) some inflatable wings to glide and thus not gain much vertical speed. Anything so it won't fall down like a brick.

[rtkwe]

You can't pull autorotation with fixed pitch blades, at least not in any meaningful manner. Light quads can fall pretty slowly with pinwheeling motors but that's not actually autorotation. The way a helicopter is able to autorotate is to pull negative pitch, which spins the rotors using the fall energy of the copter, then shortly before crashing pulling back to positive pitch and using the still spinning blades to slow down to a controlled landing.

For motor failure ETH Zurich has some research out there about recovering to normal(ish) flight after a prop loss. The quad goes into a pretty rapid spin but it's still controllable, link below to an outside the lab test.

https://www.youtube.com/watch?v=ek0FrCaogcs

[Varcht]

There is indeed some work going on with failsafe parachute deployment and one or two commercially available solutions. So far they are not very popular from what I have seen being very much involved in the hobby.