Manta Ray-Inspired Soft Robotic Swimmer for High-speed and Multi-modal Swimming

Manta rays exhibit complex motion behavior through their flexible fins. This study proposes a novel manta ray-inspired soft robotic swimmer with bistable flapping wings for high-speed and multi-modal swimming. The wings are created with prestressed bistable composite and actuated by small McKibben artificial muscles. Pressurizing and depressurizing the McKibben actuators integrated into the flapping wings generates alternating snap-throughs between two stable states, yielding swimming. Experiments are set up and conducted to analyze how the robot responses vary as a function of input pressures and actuation frequencies for both bistable and monostable modes. Experimental results show that the highest swimming velocity is 0.58 body lengths (BL) per second (equivalent to 12.23 cm/s), and the maximum turning angle speed is 22.5° per second with a smaller turning radius by holding the fins in asymmetric positions for bistable modes. Multimodal swimming motions are achieved including forward and backward translating, turning, and flip-turning.