Research on Turning Characteristics of a Biomimetic Robotic Boxfish Driven by Pectoral Fin with Two Degrees of Freedom

Turning characteristics of 2-DOF (degree of freedom) pectoral-fins propelled biomimetic robotic boxfish in three different cases are studied respectively, namely driven by unilateral pectoral fin, by two pectoral fins and by unilateral pectoral fin/caudal fin. First of all, the sinusoidal motion laws of pectoral fin and caudal fin are given. On this basis, the turning hydrodynamics models are established for the three cases. And then numerical methods are used to analyze characteristics of given-radius turnings when the fish is driven by unilateral pectoral fin, or by unilateral pectoral fin and caudal fin together, and also spot turnings when it is driven by bilateral pectoral fins. And corresponding turning conditions are also presented for each case. Experimental results show that the average angular velocity of turning achieves at 0.26 rad/s by unilateral pectoral fin and caudal fin propulsion. The maximum angular velocity of turning is at 0.314 rad/s, and the minimum radius of turning is 0.74 times of body length, when it is driven by unilateral pectoral fin. Average angular velocity of spot turning is 0.42 rad/s when it is driven by bilateral pectoral fins. Compared with the existing results, the designed robotic fish have more abundant behaviors of turning, the better maneuverability and the higher turning angular speed.