The Geometry of Single Smarticle Locomotion

We investigate an active granular medium composed of “smarticles” (smart, active particles), simple, low cost, programmable three-link, two motor robots. These robots can perform self-deformations, enabling individuals to locomote and to repel/attract each other via (dis)entanglement of arms, thereby allowing on-demand formation of gas, fluid, and solid-like states. As a result, a collection of smarticles can exhibit behaviors not typically associated with granular materials such as supporting both compressive and tensile loads. Smarticles, when placed upright on a flat surface can only change their shape, they cannot translate on their own, however, they can move collectively when confined with several other robots. When placed on their side, smarticles can crawl along flat ground while performing different gaits--sequencing their limbs in a periodic fashion. We analyzed and optimized single smarticle locomotion using the geometric mechanics framework (Shapere & Wilczek, PRL, 1987; Hatton & Choset, EPL, 2015). This theory captures and rationalizes both the direction of movement and effectiveness of different gaits along a flat surface.