Development of a turning control strategy for a bio-inspired underwater vehicle

Maneuvering in fish is complex and offers inspiration in the development of the next generation bio-inspired underwater vehicles (BUVs). Balancing desired functionality with minimal mechanical complexity is a challenge in developing a BUV. This study presents a single-actuator turning strategy for the Tunabot, a bio-inspired robotic fish, using asymmetric tail-beat timing to generate turning forces. Biological fish, such as tuna, adjust tail kinematics for maneuverability. Following this principle, the proposed control method modifies stroke duration through a single motor, synchronized by a digital encoder. Experiments were conducted in a tank, using the dorsal-view high-speed video and DeepLabCut motion tracking technology to analyze and quantify turning radius and swimming velocity. A 66% asymmetric difference in tail-beat timing resulted in a turning radius of 1.42 body lengths at a certain base frequency. Scaling laws were developed to reveal the fluid dynamics and predict the turning radius and swimming speed of the Tunabot given known tailbeat frequencies. Power consumption data was gathered for asymmetric maneuvers and compared to their symmetric equivalents. These findings demonstrate that asymmetric tail-beat control enables effective turning without dedicated steering mechanisms, offering novel insights for designing highly maneuverable underwater bio-robots with low power consumption.