Wheel transformer: A miniaturized terrain adaptive robot with passively transformed wheels

A small mobile robot that uses round wheels has a stable ride ability on flat surfaces, but the robot cannot climb an obstacle whose height is greater than the length of its wheel radius. As an alternative, legged-wheel robots have been proposed for their better climbing performance. However, such legged-wheel robots have a poor driving performance on flat surfaces since their center of mass is vertically changed. Transformable wheels are used to make the robot drive with round wheels on flat surfaces and climb an obstacle with legged-wheels. However, the design of previously developed transformable wheels is complicated because it needs actuators for the transformation. Thus, it is not suitable for small robots. In this paper, a simple robot platform called Wheel Transformer that uses a new kind of transformable wheel is described. The transformation process is passively operated by an external frictional force, so it does not need any actuators. We fabricate the transformable wheel as well as the robot platform based on analysis of transformation mechanism. The robot can climb an obstacle whose height is 2.6 times greater than its wheel radius.