Experimental Study of a Two-Joint Dolphinlike Propulsion Mechanism. 2nd Report. Experiment of Self-Propelled Large Robot.

Abstract

In this paper, we constructed a self-propelled two-joint dolphin robot as a simplified model of high-speed swimming animals. The total length of the robot is 1.75m, which is similar to the length of actual fast swimming animals. The robot is composed of a streamlined body and a rectangular caudal fin. The first joint is actuated by an air motor connected to a high pressure a air tank. The second joint is moved passively by springs. A measurement system was developed in order to measure the joint torque and joint angle of the first joint. Firstly, The body drag was measured by towing experiment. Next, swimming experiment was done to measure the joint angle and torque. By using this experimental method, we investigated the characteristics of the propulsive speed and the efficiency with respect to the spring stiffiness of the second joint and the amplitude of the first joint. It was found that the meximum propulsive efficiency did not depend much on these parameters and the robot attained a propulsive efficiency of 0.7. On the other hand, the robot attained a propulsive speed of 1.15m/s. Finally, we compared the experimental results with the theoretical ones. The experimental values show similar tendencies to the theoretical ones although they are somewhat smaller than the theoretical ones.