Implementing Flexible and Fast Turning Maneuvers of a Multijoint Robotic Fish

This paper focuses mainly on the control issues of replicating fast C-start maneuvers commonly found in fish propelled by their bodies and/or caudal fins. To generate an escape maneuver that combines a high degree of flexibility and precision, major factors related to the caudal fins, the moving joints, and the used motors are explored. Specifically, the turning rate is maximized by finely designing the preparatory and propulsive stages, while the relatively precise turning angle is achieved by a closed-loop control strategy in the propulsive and variable stages. Different types of C-starts are extensively implemented and compared by using a four-joint robotic fish. The latest results obtained show that the robotic fish is able to execute C-starts flexibly with a turning angle of up to 213 °, a top turning rate of approximately 670 °/s measured by the onboard gyroscope. Meanwhile, an upper limit of turning precision of less than 10 ° is achieved.