Design and Closed-Loop Motion Planning of an Untethered Swimming Soft Robot Using 2D Discrete Elastic Rods-based Physics Engine*

Despite tremendous progress in developing soft robots in recent years, existing systems lack the mobility, model-based control, and motion planning capabilities of their piecewise rigid counterparts. As in conventional robotic systems, the development of versatile locomotion of soft robots is aided by integrating hardware design and control with modeling tools that account for their unique mechanics and environmental interactions. Here, a framework for physics-based modeling, motion planning, and control of an untethered swimming soft robot is introduced. This framework enables co-design in the simulation of robot parameters and gaits to produce effective open-loop behaviors and enables closed-loop planning over motion primitives for feedback control of a soft swimmer. This pipeline uses a discrete elastic rods physics engine that discretizes the soft robot as many stretchable and bendable rods. On hardware, an untethered aquatic soft robot that performs frog-like rowing behaviors is engineered. Hardware validation verifies that the simulation has sufficient accuracy to find the best candidates for sets of parameters. The simulator is then used to generate a trajectory library of the robot's motion that is used in real-time closed-loop path following experiments on hardware.