With reversible motor I see no problems it would take a shitload of a motor but it could definitely work. Unfortionaly the engines of the hobby quad copters we

With reversible motor I see no problems it would take a shitload of a motor but it could definitely work. Unfortionaly the engines of the hobby quad copters we have today are not reversible without a relay. And even if they where they would not be able to change direction fast enough. One thing that could work is pitchble blades, the problem with that is that it introduces a much bigger risk for failures.