Collective transport in an entangled robotic worm blob

Through forming collectives, living and non-living systems can enable new functionalities that are not accessible to the individual. Most commonly studied swarms involve individuals that do not contact each other (fish school or drone swarms). Here, we develop a robophysical model of the collective dynamics of physically entangled collectives, worm blobs, where thousands of centimeter-long aquatic worms knot their bodies to form large-scale aggregates capable of surviving extended desiccation, mechanical impacts and directed locomotion under temperature gradients. The model consists of six 3-link, 2 motor planar robots (smarticles), with arms covered in barbs and mesh to aid entanglement. Using this robotic blob, we examine the relative importance of behaviors we observe in the living system: mechanical interactions (entanglements), differentiation of roles in the collective, and the existence of binders (force traction). The mean displacement of the robotic blob increased from 3.7±2.5 (all crawl) to 10.5±4.9 mm as the robots used the combination of three gaits. Our results reveal that gait differentiation is critical for collective movement, but synchronization is not required, and reduced activity of certain robots enhances the physical entanglement among individuals.