Modeling and system identification of three-layer structure electrostatic film motors for a robotic fish

We have developed an underwater fish-like robot using two-four-phase three-layer structure electrostatic film motors. In the robotic fish, the novel motors actuated the flexible caudal fin to propel itself via an elaborate power transmission system. In this paper, we first theoretically analyze the dynamic properties of the three-layer structure electrostatic film motors by modeling it as a 10-terminal capacitance network, and derive a high-speed open-loop swimming control strategy from the analytical results. Next, a simple theoretical model concerning the power transmission system of the robotic fish is also analyzed to provide a possible explanation for the unique swimming control. Then, we perform experimental verification of the open-loop swimming control for an improved prototype of the robotic fish. Results from experiments performed with the improved robot in an aquarium show good agreement with theoretical predictions. Finally, through these experimental results, we further clarify the relationship between the open-loop motor pattern and motion parameters.