Stanford University computer scientists have developed an artificial intelligence system that enables robotic helicopters to teach themselves to fly difficult stunts by simply watching other helicopters perform the same maneuvers. The result is an autonomous helicopter than can perform a complete air show of complex maneuvers on its own.

The stunts are "by far the most difficult aerobatic maneuvers flown by any computer-controlled helicopter," said Andrew Ng, the professor directing the research of graduate students Pieter Abbeel, Adam Coates, Timothy Hunter and Morgan Quigley.

The helicopter carries accelerometers, gyroscopes and magnetometers — the latter uses the Earth's magnetic field to figure out which way the helicopter is pointed. The exact location of the craft is tracked either by a GPS receiver on the helicopter or by cameras on the ground. (With a larger helicopter, the entire navigation package could be airborne.)

There is interest in using autonomous helicopters to search for land mines in war-torn areas or to map out the hot spots of California wildfires in real time, enabling firefighters to quickly move toward or away from them. Firefighters now must often act on information that is several hours old.

"In order for us to trust helicopters in these sorts of mission-critical applications, it's important that we have very robust, very reliable helicopter controllers that can fly as well as the best human pilots in the world can," Ng said.

Stanford's autonomous helicopters have taken a large step in that direction. Stanford's artificial intelligence system learned how to fly by "watching" the four-foot-long helicopters flown by expert radio control pilot, Garett Oku.

"Garett can pick up any helicopter, even ones he's never seen, and go fly amazing aerobatics. So the question for us is always, why can't computers do things like this?" Coates said.

It might seem that an autonomous helicopter could fly stunts by simply replaying the exact finger movements of an expert pilot using the joy sticks on the helicopter's remote controller. That approach, however, is doomed to failure because of uncontrollable variables such as gusting winds. Early on in their research, Abbeel and Coates attempted to write computer code that would specify the commands for the desired trajectory of a helicopter flying a specific maneuver.

While this hand-coded approach succeeded with novice-level flips and rolls, it flopped with more complex maneuvers.

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