1. Introduction
A ball robot [1]–[3] is a mobile designed to balance on a single spherical wheel, that is a ball. Because a ball robot contacts travel surface on single contact point, it is omnidirectional and thus exceptionally agile and maneuverable in motion compared to other ground vehicle. A ball robot has an inverted pendulum structure over a ball using some driving actuators like an acrobat uses his feet to rotate a ball and moves while balancing after he rides on a ball.