Shivam Chopra1,Saurabh Jadhav1,Nick Gravish1,Michael Tolley1
University of California, San Diego1
Shivam Chopra1,Saurabh Jadhav1,Nick Gravish1,Michael Tolley1
University of California, San Diego1
Granular media is one of the most commonly occurring substrates in natural forms such as sand, soil, seabed, and extra-terrestrial regolith. Although a considerable amount of previous work in soft robotics has explored the strategies for untethered locomotion on unstructured terrain and swimming in underwater environments, less attention has been given to the design of robots for subsurface locomotion in granular media. Locomotion in granular media is challenging due to the high depth-dependent drag forces that the robot has to overcome along with the nonhomogeneous and unpredictable nature of granular media. Additionally, the lack of computational tools to model soft, deformable structures interacting with granular media has made the optimization of such soft robotic systems extremely difficult. In this work, we present an untethered soft robot actuated by appendages for locomotion in granular media. The appendages for this robot consist of soft elastomeric actuators (soft) that bend in response to internal pressure. The change in internal pressure is caused by the phase change from liquid to gas state in a low boiling point liquid. We optimize the design of these appendages using a simulation framework to predict the non-linear response of a soft body interacting with granular media. The simulation framework is based on a one-way coupling between (a) finite-element analysis to simulate the structural deformation of the soft actuator; and (b) an empirical approach, called Resistive ForceTheory (RFT) to calculate the drag forces and thrust generated by the soft actuator to enable locomotion within the granular media. Additionally, we design a self-contained control system to generate internal pressure for actuating the appendages using a low-boiling point liquid which enables the design of a fully untethered soft robot. We demonstrate the application of this soft robot for locomotion in naturally occurring sand and in controlled lab environments.