Abstract: The coordinated turning mechanisms of the pectoral and caudal fins, as well as methods for dynamic modeling, still require further exploration to meet the need for flexible maneuverability of robotic fish in complex environments. The aim of this work is to reveal the turning mechanism of a robotic fish with coordinated pectoral and caudal fins and to establish a dynamic model for its turning motion. We studied the turning motion of a bionic fish within a given radius under the coordinated propulsion of its pectoral and caudal fins. First, a kinematic model of the coordinated propulsion of the pectoral and caudal fins was established. Three turning motion parameters were selected: phase lag and frequency lag of the pectoral fins, and body bending offset. Computational fluid dynamics numerical simulation was then employed to reveal the swimming mechanism during coordinated pectoral-caudal fin turning. Meanwhile, numerical simulation datasets were obtained for different turning parameters. Finally, based on the obtained dataset, a radial basis function neural network was employed to construct a turning dynamics model for the robotic fish, correlating the three turning metrics with its average turning speed, time, and angular velocity. By solving the inverse dynamics model, parameter values for turning motion under target radius and turning time were obtained, enabling the robotic fish to execute turning maneuvers at specified radii. To validate the model’s reliability, experiments were conducted using an independently developed robotic fish. Results showed a 5% error between experimental data and model predictions, confirming the accuracy and reliability of the established turning model. This study provides theoretical reference for turning maneuvers in robotic fish driven by coordinated pectoral fin and caudal fin movements.

Key words: Robotic fish')">Robotic fish, Co-propulsion of pectoral and caudal fins, Turning with given radius, Computational fluid dynamics, Neural network modelling