(I can't watch the video) It certainly seems plausible that it could work.
Imagine a copter with reversible motors that can respond quickly-enough (weasel words!) to inputs from the control system. Now, the copter has angular momentum along the direction perpendicular to the rotor disk and a vector between the copter's center of mass and the working motor, and further that the copter is oriented such that the vector is also parallel to the plane of the ground.
As jfoutz said, running the motor ("forward") when the copter is upright and off otherwise gives you net upward thrust (averaged over time). It also applies a torque to the copter, which will mostly be parallel to the extant angular momentum vector. So, a first-order fix is to do what jfoutz said, but also run the motor "backward" (negative thrust) when the copter is upside-down. However, rotor also generates some torque perpendicular to the rotor plane, which will cause the angular momentum vector to rise above the horizon (since the motor reverses when it is upside-down, the angular momentum vector rotates upward rather than revolving around the original direction of the angular momentum vector).
However, if you allow the copter to have some angular momentum (i.e., you don't try to completely eliminate it), the rise might be slow enough to be managed by running the motor at other times. For example, by running the motor when the rotor plane is perpendicular to the ground, you could create a similar drift in the angular momentum vector. But now it slowly drifts around the compass instead of rising above the horizon. If you make the "compass" drift faster than than the "altitude" drift, the torque from the first one will average out to something very small. So by managing the rate of these two drifts with an appropriate feedback loop, you can probably obtain a stable solution where there is a net upward thrust and the angular momentum vector "slowly" (for possibly large values of slow) precesses along the horizon.
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.
Imagine a copter with reversible motors that can respond quickly-enough (weasel words!) to inputs from the control system. Now, the copter has angular momentum along the direction perpendicular to the rotor disk and a vector between the copter's center of mass and the working motor, and further that the copter is oriented such that the vector is also parallel to the plane of the ground.
As jfoutz said, running the motor ("forward") when the copter is upright and off otherwise gives you net upward thrust (averaged over time). It also applies a torque to the copter, which will mostly be parallel to the extant angular momentum vector. So, a first-order fix is to do what jfoutz said, but also run the motor "backward" (negative thrust) when the copter is upside-down. However, rotor also generates some torque perpendicular to the rotor plane, which will cause the angular momentum vector to rise above the horizon (since the motor reverses when it is upside-down, the angular momentum vector rotates upward rather than revolving around the original direction of the angular momentum vector).
However, if you allow the copter to have some angular momentum (i.e., you don't try to completely eliminate it), the rise might be slow enough to be managed by running the motor at other times. For example, by running the motor when the rotor plane is perpendicular to the ground, you could create a similar drift in the angular momentum vector. But now it slowly drifts around the compass instead of rising above the horizon. If you make the "compass" drift faster than than the "altitude" drift, the torque from the first one will average out to something very small. So by managing the rate of these two drifts with an appropriate feedback loop, you can probably obtain a stable solution where there is a net upward thrust and the angular momentum vector "slowly" (for possibly large values of slow) precesses along the horizon.