How to Achieve Maneuverability and Adaptability in an Underactuated Robotic Fish by using a Bio-inspired Control Approach

Biomimetic robotics can help support underwater exploration and monitoring while minimizing ecosystem distur-bance. It also has potential applications in sustainable aqua-farming management, biodiversity preservation, and animal-robot interaction studies. This study proposes a bio-inspired control strategy for an underactuated robotic fish, which utilizes a single DC motor to drive a mechanism that converts the motor's oscillating motion into an oscillatory motion of the robotic fishtail through a magnetic coupling and a wire-driven system. The proposed control strategy for the robotic fish is based on central pattern generators (CPGs) and incorporates proprioceptive sensory feedback. The torque exerted on the fishtail is adjusted based on its position, allowing for increased or decreased body speed and steering with different angular speeds and radii of curvature despite the underactuated design. The robotic fish can vary the swimming speed of 0.08 body lengths per second (BL/s) with a related change in the tail-beating frequency up to 2.3 Hz, and it can vary the steering angular speed in the range of 0.08 rad/s with a relative change in the curvature radius of 0.25 m. The controller can adapt to changes in tail structure, weight, or the surrounding environment based on the proprioceptive feedback. Design changes to the modular design can improve speed and steering performances, maintaining the control strategy developed.