Biomimetic Robotic Sea Lion Foreflippers: Design, Modeling, and Experimentation

Otariidae are excellent swimmers and the only ones among the marine mammals that use foreflippers for propulsion. Taking California sea lion as the bionic prototype, this article proposed and developed a biomimetic robotic sea lion foreflipper device (robotic flipper for short), which is composed of a pair of bionic flippers and a serial mechanism consisting of a wobbling coin mechanism and a RSSR spatial crank-rocker mechanism. The attitude and motion characteristics of the bionic flipper were obtained based on the kinematic analysis of the robotic flipper. Kinematic analysis and tank experiments show that the robotic flipper can effectively imitate the motion characteristics of the sea lion foreflipper. In addition, it can also obtain different flipper tip trajectories by adjusting the length of the connecting rod of the RSSR mechanism, and the generated thrust from the trajectory like sea lion foreflipper is larger than that from other flipper tip trajectories. A higher clapping frequency can generate a higher thrust, and the bionic flexible flipper has higher thrust and thrust efficiency than the rigid one. A larger pitch angle of the robotic flipper can result in a larger peak thrust but not always a larger average thrust. The present robotic flipper shows a better thrust performance at the pitch angle of 15°.