Adaptive multimodal swimming gaits in a reconfigurable modular soft robotic fish.

Fish swim with four main gaits-anguilliform, subcarangiform, carangiform, and thunniform-produced by waves along varying portions of the body. However, how muscle activation length influences swimming performance remains poorly understood. We present a reconfigurable robotic fish that replicates all four gaits in a single platform by rapidly tuning its body stiffness. Vacuum-driven layer jamming muscles in four tensegrity joints enable quick (≤1 s) stiffness modulation (stiffness ratio of 46.6) and gait switching. In thunniform gait, the robot reaches 1.24 body lengths per second, whereas in anguilliform gait, it achieves agile maneuvering with a turning radius of 0.26 body lengths. Fluid simulations show that the thunniform gait generates stronger vortices and 142% more thrust compared with anguilliform motion at 5 Hz, explaining its high-speed performance. The robot dynamically adapts gaits during locomotion-using thunniform for fast traversal and anguilliform for obstacle negotiation-demonstrating environmental adaptability. This work advances understanding of aquatic multimodal locomotion.