This pair of quad-rotor helicopters does a better job of keeping a ping-pong ball in the air than we could. The two flying drones are performing inside of the flying machine arena, a 1000 cubic meter indoor space surrounded by nets with a foam-padded floor. This makes for a prototype-friendly space, protecting the copters from hard landings and the experimenters from the maiming that might accompany a runaway robot.Via Hack a day