Kinematic analysis and positioning performance evaluation of a structurally stability-enhanced ballbot

Ballbots are advanced mobile robots which actively balance on a single spherical ball, and has the benefits of (a) omni-directionality (b) single contact point with the ground and (c) dynamic stability. Ballbot models which have been previously developed used an inverted mouse-ball drive and a three omni-wheel system to transmit power to the ball. The earliest design used four rollers located at the lower half of the ball while the later designs used omni-wheels located at the upper half of the ball to drive the ballbot. In this paper, a novel design of ballbot is suggested. In the proposed model, the omni-wheels are relocated to the bottom half of the ball, reducing the overall height of the mobile robot. The ball of the ballbot makes contact with other elements at five points out of which three points are used for actuation. In the ballbot, the rotational movement of the omni-wheels was transformed into planar movement. The velocity kinematics of the robot was derived using differential motion transformation. The positioning performance of the ballbot was evaluated using a coordinate measuring machine and reference ball setup and the positioning error was determined.