Helicopters are tricky beasts to keep aloft and stable. Full-size birds do it with skilled pilots, while most unmanned craft rely on gyroscopes and autopilot. But the 3.3-gram Picoflyer is too small for any such luxuries. Instead, Petter Muren, a Norwegian engineer who builds mini copters to fly indoors during long Scandinavian winters, reinvented the stability system.

To stay pointed in one direction, the Picoflyer, like many real whirlybirds, uses two sets of counter-rotating rotors, which offset the opposing forces that occur when an engine drives a propeller in flight.