Form and Locomotion of Magnetically Driven Soft Robots in Sediment Beds

We study the shape and locomotion of a soft robot with a magnet head and elastic tail in fluid-saturated granular media driven by an oscillating magnetic field. Our studies are motivated by soft robot designs based on biomimetic principles which organisms exploit in response to the surrounding environment and stimuli. The applied oscillating field, magnetic field strength, and filament tail length, along with the sediment volume fraction and depth are control variables, in our study. Exploiting refractive index matching of the grains, we measure the shape and speed of the robot over time. A transition from reciprocal to anguilliform body is observed because of subtle balance of drag, propulsion, and elastic restoring forces. We will discuss the impact of the change of gait on the nonlinear increase of swimming speed observed with driving frequency.