Operation of the Ballbot on Slopes and with Center-of-Mass Offsets

The ballbot is a human sized, dynamically stable mobile robot that balances on a single, spherical wheel. The current framework for navigation and control makes the assumption that the robot is operating on a level surface without any center-of-mass offset; however, in practice, such a dynamically stable robot has to be able to successfully navigate sloped surfaces and with such offsets. This work develops the equations of motion for the ballbot system on a sloped surface with a center-of-mass offset. The equilibria of this system are analyzed, and a compensation strategy is formulated that allows the ballbot to operate in the presence of slopes and center-of-mass offsets. This work also develops estimation algorithms for slope and center-of-mass offset angles during station-keeping and trajectory following. Results for compensation and estimation are demonstrated experimentally.