"The Ballbot: An Omnidirectional Balancing Mobile Robot"
by Umashankar Nagarajan, George Kantor, and Ralph Hollis
International Journal of Robotics Research 33(6): 917-930
http://dx.doi.org/10.1177/0278364913509126
The ballbot is a human-sized dynamically stable mobile robot that balances on a single ball. Unlike statically stable mobile robots, the ballbot is tall and narrow with a high center of gravity and a small footprint. Moreover, its dynamic stability enables it to be physically interactive. These characteristics make it better suited to navigate and interact in cluttered human environments. This paper presents the evolved hardware design of the ballbot with a four-wheel inverse mouse-ball drive to actuate the ball, and a yaw drive mechanism that enables unlimited rotation about its vertical axis. The ballbot also has a triad of legs that provide static stability when powered down. This paper presents a detailed description of the ballbot's control architecture, and it presents several experimental results that demonstrate its balancing and locomotion capabilities. This paper also presents a trajectory planning algorithm that plans for body lean motions, which, when tracked, result in the desired rest-to-rest motions of the robot. Finally, the paper illustrates some interesting human--robot physical interaction behaviors that can be achieved as a result of the ballbot's dynamic stability.
