Analysis of Kinematics and Propulsion of a Self-Sensing Multi-DoF Undulating Soft Robotic Fish

In this paper we explore kinematics ranging from anguilliform to thunniform achieved in a self-sensing multi-degree-of-freedom soft robotic fish and analyze the effect of them on the swimming. First, we examine the characteristics of the bending actuators of the robotic fish. Then, we express the kinematics of the fish as a propagating wave parameterized by three bending amplitudes and a wavelength, which are determined by the flow rates and phase shift of the pumps. We capture various motion patterns generated by different actuator inputs and directly measure the thrust generated by each pattern. We observe that the robotic swimmer can reproduce two different modes of propulsion, that are embodied by two distinct morphological patterns in nature: anguilliform and thunniform. When neither of modes are activated, propulsion is zero or even negative. Finally, we estimate the stationary swimming speed by towing the undulating fish, which satisfies the slip condition (with the speed of the body wave matching the swimming velocity). The analysis of a wide range of kinematic patterns in this study, including two extreme cases of anguilliform and thunniform modes, will provide insights for comprehensive understanding the mechanics of efficient swimming.