Stair climbing capabilities of USU's t3 ODV mobile robot

A six-wheeled autonomous omni-directional vehicle (ODV) called T3 has been developed at Utah State University's (USU) Center for Self-Organizing and Intelligent Systems (CSOIS). This paper focuses on T3's ability to climb stairs using its unique configuration of 6 independently driven and steered wheels and active suspension height control. The ability of T3, or any similar vehicle, to climb stairs is greatly dependent on the chassis orientation relative to the stairs. Stability criteria is developed for any vehicle dimensions and orientation, on any staircase. All possible yaw and pitch angles on various staircases are evaluated to find vehicle orientations that will allow T3 to climb with the largest margin of stability. Different controller types are investigated for controlling vertical wheel movement with the objective of keeping all wheels in contact with the stairs, providing smooth load transfer between loaded and unloaded wheels, and maintaining optimum chassis pitch and roll angles. A controller is presented that uses feedback from wheel loading, vertical wheel position, and chassis orientation sensors. The implementation of the controller is described, and T3's stair climbing performance is presented and evaluated.