Bistable actuator tuned via flexible hinges for bioinspired jellyfish robot

With the deepening exploration and research of marine resources, bioinspired underwater soft robots are playing an increasingly important role. As a paradigm of highly efficient locomotion in the ocean, jellyfish have attracted extensive attention in the field of underwater bioinspired robots, owing to their unique umbrella-shaped bodies and efficient pulsed jet propulsion mechanism. Inspired by the pulsed propulsion of jellyfish and the steering of box jellyfish via tentacles, this study designs and fabricates a bioinspired jellyfish robot driven by a hybrid of composite bistable actuators and Fiber-Reinforced Soft Actuators (FRSA). The bistable actuator acts as a flexible hinge by thinning local beam segments, enabling precise regulation of the snap-through force and released energy. To optimize the underwater propulsion performance of the robot, a fish-fin-like structure is designed and fabricated. Hydrodynamic analysis via ANSYS FLUENT indicates that, among the three assembly angles investigated, the 45° configuration yields the most favorable propulsive performance. The bioinspired jellyfish robot reaches a maximum instantaneous locomotion velocity of 6.4 cm/s and an average velocity of 5.6 cm/s, and realizes the steering function by means of FRSA. In addition, the jellyfish robot exhibits excellent underwater load locomotion capability, achieving a locomotion velocity of 3.5 cm/s when carrying a 200 g counterweight, which further validates the outstanding locomotion performance of the proposed jellyfish robot. We also calculated that the cost of transport(COT) of the robot is 0.25. This study provides new design concepts and practical foundations for developing soft robots with both high locomotion performance and low energy consumption.