Stabilizing the head motion of a robotic dolphin with varying the stiffness of a caudal fin

Various oscillating parameters have been used to increase the velocity of a robotic dolphin. Among them, an efficient and easy way to increase the thrust is to increase an oscillating frequency of the robotic dolphin. However, there is a trade-off. If the oscillating frequency increases, the stability of the robotic dolphin decreases. Especially, a reactive motion is occurred in a head of the robotic dolphin due to the fluctuating motion of a caudal fin. The unsteady motion in the head position can be controlled using an additional actuator. However, the best solution is to reduce an undesired motion without adding the actuator. In this paper, to reduce the fluctuating problem, we consider the flexibility of the caudal fin. An oscillating amplitude of the caudal fin and head motion is changed with varying the stiffness of the caudal fin. Therefore, if we find the appropriate stiffness of the caudal fin, the head motion can be stabilized.