PITTSBURGH-Carnegie Mellon University researchers have developed a new type of mobile robot that balances on a single urethane-coated metal sphere instead of legs or wheels.

The 95-pound "Ballbot," as it is called, is a self-contained, battery-operated robot that balances dynamically on the sphere and is about the height and width of a person. Because of its long, thin shape and ability to maneuver in tight spaces, it has the potential to function better than other types of robots in environments with people.

"We wanted to create a robot that can maneuver easily and is tall enough to look you in the eye," says project leader, professor Ralph Hollis. "Ballbot is tall and skinny, with a much higher center of gravity than traditional wheeled robots. Because it is omnidirectional, it can move easily in any direction without having to turn first."

Ballbot has an onboard computer that reads balance information from set of internal sensors and then activates a series of rollers that mobilize the ball on which it moves-essentially the inverse of what happens with a computer mouse-ball drive. When Ballbot is not in operation, it stands in place on three retractable legs.

According to Hollis, Ballbot is part of an ongoing effort to find a simple alternative to "legged" robots, like Honda Motor Co.'s Asimo, which are both complex and expensive.

For more information, visit www.msl.ri.cmu.edu/projects/ballbot/.