Polysectoid: a hyperredundant soft-bodied robot for modeling the role of parapodia in undulation and peristalsis

Biological inspiration offers new and innovative solutions to exploring challenging terrains, and implementations in bio-inspired robotics in turn offers insights to biological form and function. In particular, annelids (segmented worms), such as Nereis sp. (bristleworms), are useful subjects for their multi-modal locomotion through differing environments. This research aims to mimic key anatomical features of nereid worms in order to develop a new bio-inspired soft robot, named "Polysectoid," that effectively moves through challenging terrains using both peristalsis and undulation. The muscles of the tendon-driven soft robots are longitudinal, and the robot has protruding structures mimicking parapodia and chaetae. Taking advantage of these features for both undulation and peristalsis required a new structural design to achieve both large bending motion and large diameter changes. Thus, the robot's body is constructed of many long strips of flexible polymer, connected with custom 3D-printed channel pieces. We compare effectiveness and efficiency of movements of the resulting robot on substrates with different textures and in confined spaces. Parapodia and chaetae improve robot performance, with different effects on different gaits and substrates. Peristalsis with long parapodia allows Polysectoid to stay on a straightforward trajectory even without steering control. On the other hand, undulation allows the robot to navigate well in tight spaces, such as sandwiched between parallel surfaces, even when the distance between the parallel substrates was reduced to 66% of the robot's diameter. This type of undulatory motion could have novel applications in inspections of confined spaces. As a detailed physical model, this design provides a platform to further examine the biomechanics of annelid-inspired locomotion and cascading neural pattern generator-based networks.