Design and Characterization of a Fully Autonomous Under-actuated Soft Batoid-like Robot

Batoids use their large pectoral fins to achieve unique maneuverability and propulsive performance. In this work, the design, fabrication and characterization a soft batoidlike robot is presented. The robot is designed to mimic undulatory rajiform locomotion. The design is under-actuated, simple and robust and well suited for propulsive performance experiments thanks to its full autonomy, long battery life, and wireless recharging capabilities. The robot has a 180mm body length, a maximum flapping amplitude of 60deg, and reaches a peak speed of 0.93 body length per second. In order to characterize its swimming kinematics and propulsive forces a special setup was built using an instrumented holder and high speed video. Experiments were conducted to characterize propulsive force generation with varying fin flapping frequencies (from 1hz to 2.4hz), amplitudes, and wavelengths. The results show that while both flapping frequency and amplitude influence propulsive forces, for the locomotion modes tested, flapping frequency has a stronger effect on both thrust and side forces. Furthermore, larger side forces than thrust forces are produced for the same swimming parameters.