Abstract
Fish have endured millions of years of evolution, and their distinct rigid-flexible body structures have offered limitless inspiration for developing biomimetic robots. The current paper introduces a fish spine-like rigid-flexible transition structure and thus leads to scalable prototypes of biomimetic robotic fish. Inspired by fish anatomy, the structure incorporates expandable fishbone-like ribs with adjustable magnets to emulate the stretch and recoil of fish muscles, thus balancing the easy implementation of rigid actuators with enhanced flexibility. Notably, such a structure is capable of full-body modular packaging, allowing for rapid expansion and adaptation to different fish shapes and swimming modes. To optimize the hydrodynamics of the robot, we employed an evolutionary algorithm, resulting in a significant enhancement in free swimming performance. At last, we demonstrate the robustness of the constructed biomimetic robotic fish in a natural water environment, showing its real-world monitoring capabilities.