EMBUR (EMerita Burrowing Robot): A Robophysical Exploration of Mole Crab Burrowing*

Despite the ubiquity of granular substrates like sands and soils in the natural environment, few robots are capable of burrowing vertically under their own self-weight, and even fewer can do so using legs. In this work, we discuss prior research on a novel mole crab-inspired robot– EMBUR (EMerita Burrowing Robot) –  and how it has been used as a tool for robophysical exploration of legged burrowing. EMBUR’s design was guided by an initial study of the Pacific mole crab, Emerita analoga. E. analoga has five leg pairs, which on the robot are functionally simplified into two counter rotating leg pairs. The mole crabs also employ a complex leg trajectory which reduces resistive force during part of their cyclical stroke. Similarly, the legs of EMBUR are flexible and can extend and retract to create anisotropic force response. We observe parallels between the robot’s and animals’ body pitch during intrusion, as well as their spatial burrowing trajectories, suggesting that EMBUR and E. analoga employ similar excavative mechanisms for burrowing. We also explore the applications of Granular Resistive Force Theory, or RFT, to the design and implementation of EMBUR. Through parametric studies, we show that RFT can predict leg geometries and behaviors which maximize desired parameters of interest. Current research focuses on understanding discrepancies between RFT predictions and observed robot behavior, and improving the robot’s control strategies using insights from more advanced modeling techniques.