Design, Fabrication, and Characterization of an Untethered Amphibious Sea Urchin-Inspired Robot

Sea urchins can easily navigate a wide range of challenging environments through the coordinated action of thousands of individually addressable rigid protective spines and flexible, reversibly adhesive tube feet. To investigate the potential implementation of these unusual locomotory appendages in a robotic context, we describe here the design, fabrication, and characterization of an untethered sea urchin-inspired robot driven by fluidic soft actuators. Due to the intrinsic design and fabrication difficulties in attempting to replicate the complexity of an adult sea urchin, we instead focused our attention on the development of a design that closely mimicked the body plan of an anatomically much simpler post-larval juvenile urchin. Consistent with its biological counterpart, our robotic prototype contained five flexible tube feet and ten rigid spines that could be independently driven by soft tripod actuators. Through the incorporation of permanent magnets into the distal ends of the flexible tube feet, our sea urchin-inspired robot could easily navigate across ferrous surfaces while adopting gaits and defensive postures that were surprisingly similar to its biological analog.