An untethered soft cellular robot with variable volume, friction, and unit-to-unit cohesion

Abstract

A fundamental challenge in the field of modular and collective robots is balancing the trade-off between unit-level simplicity, which allows scalability, and unit-level functionality, which allows meaningful behaviors of the collective. At the same time, a challenge in the field of soft robotics is creating untethered systems, especially at a large scale with many controlled degrees of freedom (DOF). As a contribution toward addressing these challenges, here we present an untethered, soft cellular robot unit. A single unit is simple and one DOF, yet can increase its volume by 8x and apply substantial forces to the environment, can modulate its surface friction, and can switch its unit-to-unit cohesion while agnostic to unit-to-unit orientation. As a soft robot, it is robust and can achieve untethered operation of its DOF. We present the design of the unit, a volumetric actuator with a perforated strain-limiting fabric skin embedded with magnets surrounding an elastomeric membrane, which in turn encompasses a low-cost micro-pump, battery, and control electronics. We model and test this unit and show simple demonstrations of three-unit configurations that lift, crawl, and perform plate manipulation. Our untethered, soft cellular robot unit lays the foundation for new robust soft robotic collectives that have the potential to apply human-scale forces to the world.