Addressing Foot Geometry Trade-Offs to Achieve Amphibious Surf Zone Transitions with a Crab Robot

Crabs have specialized curved dactyls that can be used during locomotion to anchor and control penetration in dry and wet substrates. To investigate the effect of crab leg’s geometry, we added rings similar to ski pole baskets around the dactyl to show that distributing ground reaction forces over a larger surface area would permit our crab-like hexapod Sebastian to carry heavier loads and reduce cost of transport by controlling dactyl penetration depth. The rings help prevent slip, enabling the robot to walk farther and more efficiently in dry sand with payload. The results show a trade-off between locomotion efficiency with payload and anchoring force. We then developed a new dactyl which enabled Sebastian to successfully walk from being fully submerged through the transition zone on to dry land. This research aims to help other researchers to develop inexpensive robots for efficient shallow water locomotion in the future.