Actuation mechanisms for biologically inspired everting toroidal robots

Inspired by the pseudopod mobility mechanism found in amoebas, we propose a toroidal robot which can fold in on itself to generate the same overall motion of the amoeba. One of the advantages of such a robot is its ability to squeeze under obstacles and through holes smaller than its nominal diameter. These abilities make it particularly well suited for unstructured and highly constrained environments such as medical and search and rescue applications. We present several actuation mechanisms which are being investigated towards the development of an everting toroidal robot. For smaller scale applications, we present contracting ring actuators made up of shape memory alloy rings or electroactive polymer rings that create a differential stress and drive the motion. For larger scale applications, we present a tape spring mechanism which uses a membrane composed of treads arranged in a circular pattern. Another large scale mechanism uses a snake-like robot that can be formed into a torus which can ascend and descend cylindrical structures. We also present a chemical actuation method which utilizes chemically induced swelling in crosslinked polymers to produce forward motion. Finally, we describe a novel torus shaped actuator being developed which uses shape memory alloy rings to generate an everting motion.