Minimalist Design of a 3-Axis Passive Compliant Foot for Sprawling Posture Robots

A sprawled posture amphibious biorobot resembling a salamander had helped us in conquering scientific questions of the locomotion of these animals and offer us with technological possibilities for applications in disaster response. However, so far the foot structure of these robots is simplified in a ball foot that occludes many interesting aspects of the rich dynamics of interaction with the ground that these animals/robots have. In this paper, we present a minimalist design of a three degree of freedom foot that uses passive mechanics, soft materials and simple fabrication techniques to achieve features observed in sprawling posture animals walking gaits. The parameters of our design can be adjusted for specific visco-elastic properties (stiffness, damping) and easily adapted to different sizes and forms. We presented the fabrication technique used to achieve several configurations of the foot structure. Stress analysis of the design helped us to verify the right selection of materials and configurations to achieve desired behaviors. We expect to use these feet for better understanding the limb-ground interaction in sprawled animals as well as improving the locomotion capabilities of biorobots in general.