Peristaltic Locomotion of a Modular Mesh-Based Worm Robot: Precision, Compliance, and Friction

Effective worm-like gaits require accurate segment coordination. However, there can be imprecision due to segment-to-segment variation in the soft structure, variation in actuator response to loads, or nonlinearities not compensated for in control. Here, our objective is to demonstrate how body softness with respect to frictional loads determines a tolerance for the controlled coordination of worm-like segments. To explore this, our new soft robot, compliant modular mesh worm, utilizes compliant mesh segments that are individually actuated with different waveforms that result in peristaltic locomotion. The modular mesh is constructed from 3D printed and commercially available parts, allowing for the testing of a variety of components that can be easily interchanged to vary stiffness. A series of experiments were performed to characterize the actuated mesh and the behavior of segment contact points during locomotion. In our robot, video analysis shows slip along the ground that is explained by sources of imprecision that are greater than tolerances specified by friction and compliance. The six-segment robot is faster on surfaces with greater friction (where slip is minimized) and can advance at 25.8 cm/min on a plywood surface. The data presented highlight the importance of lifting advancing segments off the ground and the role of sources of imprecision in the control of segment length. These analyses will be useful for the design and control of future peristaltic devices for new applications.