A transformable wheel robot with a passive leg

In this paper, we present a novel wheeled robot that transforms from a circled configuration to a spoke-like legged configuration. Wheeled mobile robots are able to quickly and efficiently move on flat surfaces. However they may sink into a terrain with dynamic surface such as snow, sand, dirt, moss, and small gravel. The transformable wheel robot presented in this paper is able to overcome obstacles and navigate these dynamics surfaces, yet can still move quickly over flat ground. The wheel is comprised of five spokes or legs, four of which are actively driven by a motor via four slider-crank linkages. The last one is designed be passive in order to significantly decrease the actuation force of the transformer mechanism. Analysis shows that the maximum driving force required to actuate the passive leg design is 1/187.5 times that of the active leg design. Experiments demonstrate that the passive leg design allows the mobile robot to open the transformation mechanism with a maximum external loading of 1.809 times the original robot weight. The diameter of the legged configuration wheel is 1.576 times that of the circled configuration.