Automatic Transition of Ballbot from Statically Stable State to Dynamically Stable State

Abstract

Dynamically stable mobile robots with a high center of gravity and a small foot print are breaking new ground in the field of mobile robotics. While in operation, these robots are dynamically stable, relying on inertial forces to maintain pose. And when not in operation, they rely on legs or kick stands to maintain static stability. The transition between the dynamic and static state should be automatic and smooth so as to give these robots truly autonomous capabilities. Ballbot has three retractable legs arranged in tripod configuration. Each leg is a servo controlled four bar slider crank mechanism with 1 DOF. In this work we explore means of automatic transition in Ballbot, by taking advantage of the properties of the leg mechanism. We consider two such methods, lean and take-off, and simultaneous withdrawal. We come up with generalized design intent for designing leg mechanisms to be used in dynamically stable robots. We also present the kinematic analysis of the spatial mechanism formed when the body and legs are taken together as a single mechanism.