There are a growing number of tasks that require subterranean locomotion and while there are previous studies on burrowing robots, implementing burrowing behaviors in legged robots is a largely unexplored area, due to significant design and control challenges. Emerita analoga, the Pacific mole crab, is a natural biological inspiration for developing multimodal legged robotic systems capable of burrowing in granular media. E. analoga uses two groups of limbs that expand and excavate substrate to rapidly burrow in intertidal sand. Experiments of physical robots, that leverage design and control principles used by E. analoga to burrow, establish the importance of developing limbs that can reduce drag on recovery strokes, and motivate developing a simulation model to quickly model and test parameters. We find that design parameters such as limb lengths have a strong effect on depth reached and the angle of burrowing. Our simulation results also show the importance of coordination between the two limb groups for burrowing and we provide an approximation of a local connection between limb phase and burrowing depth. These results can guide and improve the development of legged burrowing robots. Finally, the simulation environment developed for our experiments is parameterized and configurable to facilitate further study of legged robotic models in granular media.




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