Gait switching enables body pitch modulation during legged burrowing in granular media

Subsurface exploration is accomplished by few legged robotic systems, yet performed by numerous animals. In our previous work, a mole-crab inspired robot (EMBUR 1.0) self-burrowed vertically by excavating granular media with counter-rotating leg pairs. EMBUR 1.0 had two modes of burrowing: one where its body pitch increased from its initial value, and a second mode where its pitch decreased from initial. These modes limit the achievable burrow depth. We note that the real mole crab maintains a more intermediate body pitch.We hypothesize that EMBUR can regulate its body pitch during burrowing to increase the achievable burrow depth and reliability. This work introduces EMBUR 2.0—an updated self-burrowing robot capable of body pitch control. A simulation based in 2D granular resistive force theory predicts unstable regions for operation, and suggests methods for modulating pitch by changing the direction of motion of each leg pair. Gait switching allows EMBUR 2.0 to adjust its pitch to recover from an increasing or decreasing body pitch mode. We characterize how interchanging between three gaits at varying body pitch thresholds influences burrowing trajectory. This work shows that discontinuous gait changes improve performance, and should be considered in legged self-burrowers.