Robotic ray driven by periodic ring snapping

The locomotion strategies adopted by animals have been continuously optimized through the long history of evolution. The locomotion of fish, adapted to their appearances, exhibits high efficiency, superb maneuverability, and excellent stealth. Inspired by the swimming gait of Taeniura lymma, we develop an untethered, soft robotic fish that can realize continuous, stable directional underwater movement via the periodic, reversible mechanical deformation of flexible rods and films. The fish is driven by the elastic-snapping-induced shape transition of the rods, which can be controlled by only one actuator. Theoretical analysis and numerical simulation are carried out to investigate the post-buckling morphological evolution of the bioinspired design. In a deformation period, the elastic strain energy of the rods first increases slowly up to a critical value, beyond which the snap-through is triggered and the elastic strain energy stored in the rods is released rapidly. The relation between the mechanical responses of the fish and its structural parameters is revealed. Further, several physical prototypes are fabricated and tested to validate the swimming performance of our bionic design. It is found that the robotic rays can swim efficiently, stably, and quietly, with the advantage of convenient control. In comparison with existing underwater robots, our robotic ray is featured by moderate swimming speed and substantially lower energy consumption. This work holds promise in the design of shape morphing robots and other soft machines.