Optimization-Based Nonimpact Rolling Locomotion of a Variable Geometry Truss

A variable geometry truss (VGT) is a modular truss-structured robot consisting of linear actuators and three-degree-of-freedom joints. Having a sophisticated structure, the VGT can easily be damaged when it rolls and impacts the ground. This letter proposes a nonimpact rolling locomotion scheme to avoid VGT damage. It is assumed that the VGT moves quasi-statically and maintains a static stability. There exists a control phase and a rolling phase during locomotion. During the control phase, the VGT can freely move its center of mass within the supporting polygon. During the rolling phase, the VGT's center of mass is fixed at the edge of the support polygon, and it tilts forward until a node touches the ground to make a new support polygon. This algorithm optimizes the velocity of the VGT's nodes at every time step so that the center of mass follows a desired trajectory of rolling motion. A simulation verifies that the algorithm ensures that the VGT maintains its static stability, does not tumble, and accurately follows its desired trajectory.