Exploiting Geometrical Frustration in Multistable Soft Robots Part 1: Controlled Underactuation*

Leveraging instabilities offers exciting opportunities to simplify the actuation of soft robots. A key roadblock for the widespread adoption of soft robotics lies in the difficulty of commanding desired kinematic configurations, a process that often requires sensor arrays and complex closed-loop control. We present a class of soft robots with encoded multiple accessible, stable states that provide a route to shape reconfiguration without closed-loop control. Informed by the mechanics of hierarchically multistable metastructures, we design coexisting states resembling different actuation modes in soft manipulators, including grasping and twisting. We exploit the presence of geometrical frustration to access such functional global states using a limited number of actuators and primitive open-loop control. This is achieved by leveraging distinct spatiotemporal inversion sequences to access desired coexisting states on-demand.  Our strategy offers a new route for controlling soft multistable robots exploiting their strong nonlinear mechanics to the designer’s advantage.