Photo: Robot balances, rides on a ball

Robots and legs aren't yet a winning combination, so researchers at Carnegie Mellon University have devised an alternative. The Ballbot balances on a single urethane-coated metal ball, a design intended to make it omnidirectional and better able to navigate among people than lower, squatter robots. It was created by Carnegie Mellon professor Ralph Hollis, seen here.

The tall 95-pound machine functions somewhat like a mouse ball, except in reverse: Internal sensors provide balance information to an on-board computer to activate rollers that mobilize the ball. When it's not moving, Ballbot uses three retractable legs to stay standing. So far, researchers have set it in motion on carpeted surfaces. Future designs could include a head and a pair of arms--swinging the arms would help the robot balance and turn.