Ascending Technologies has added wireless charging capabilities to its quad-rotor Hummingbird. In the video, the autonomous flying robot charges itself by flying close to a charging station on the ceiling. Power transfer for the flyer uses magnetic resonant coupling, pioneered in 2007 by MIT researchers who founded the company Witricity. The coil of wire on the ceiling uses magnetic fields to drive electric current through a similar coil on the robot, transmitting small amounts of energy whenever the coils are close enough. The most interesting part of the video, in my opinion, is the light on the base station that gives a very visual indication of how much power is being transferred depending on the robot's distance and orientation. This offers a beautiful illustration of why widespread adoption of wireless charging technology has been so slow: you have to be pretty close for any significant power transfer.