Bio-Inspired Terrestrial Motion of Magnetic Soft Millirobots

Magnetic soft robots have the combined advantages of contactless actuation, requiring no on-board power source, and having flexible bodies that can adapt to unstructured environments. In this study, four milli-scale soft robots are designed (Inchworm, Turtle, Quadruped, and Millipede) and their actuation under external magnetic fields is investigated with the objective of reproducing multi-limbed motion patterns observed in nature. Magnetic properties are incorporated into a silicone polymer by mixing in ferromagnetic microparticles before curing. The magnet-polymer composite is used to fabricate soft magnetic parts, with pre-determined magnetization profiles achieved using a 1 T field. The resulting soft robots are actuated under external magnetic fields of 10–35 mT which are controlled using an array of six electromagnetic coils. The achieved motion patterns are analyzed over five iterations and the motions are quantified in terms of body lengths traversed per actuation cycle and speed of displacement. The speed of the specimens is calculated to be in the range of 0.15–0.37 mm/s for the actuation field used here. The ability of the soft robots to traverse uneven terrain is also tested, with the Turtle and the Millipede demonstrating successful motion.