Stowable Tape Spring Truss Leg for Robotic Mobility

Abstract

Obstructed terrains, such as boulders, crevices, and rubble, limit the locomotion of wheeled mobile robots. Transformable wheel-to-leg designs enable better traversal; small wheels provide driving efficiency and deployable legs enable stepping over obstructions. We propose an approach to such leg deployment utilizing a novel tape spring truss structure. It achieves large shape changes -- demonstrating transformation ratios from 3.77 to 5.38 between wheel radius and leg length -- in a light-weight (8 g) and compact way. Prior tape spring mechanisms have not yet used a string-tensioned truss formation. By tensioning the tape spring via a string mechanism, the wheel’s emerging deployable legs are strong enough to traverse obstacles greater than one wheel diameter. Yet, it can also be stowed using just the weight of the rover to coil the tape spring. Adjusting the string pretension allows for optimization of the leg’s transverse buckling load, resulting in a strong truss despite low mass and stowed volume. We validate the truss’s capability by incorporating it into a two-wheeled mobile rover platform, demonstrating utility in mobility across obstructed terrain.