Mechanical design and implementation of a bio-inspired robotic fish with flapping foils

This paper aims to build a robotic fish propelled by two oscillating pectoral fins. The prototype is designed dorsoventrally flattened and streamlined body mimicking the body shape of the Cownose Ray. To realize the similar flapping motion of nature fish, a new bionic flapping foil which combines the active and passive deformation abilities is initially proposed. A spatial parallel mechanism (SPM) is designed to actively control the deformation near the fin root. A bionic skeleton with distributed flexibility is built to obtain passive deformation. To verify the feasibility of this design scheme, a series of underwater swimming experiments are carried out with the prototype in a water tank. The experimental results show that the prototype can both obtain fast swimming speed and excellent maneuverability. A maximum swimming speed of about 0.46 m/s (or 1 BL/s) is reached when the flapping frequency is 1 Hz, amplitude 30° and phase difference 40°. Moreover, the turning radiuses of the prototype are kept very small regardless of whether the traditional turning way or the enhanced way is adopted, and the maximum turning speed is up to 60° per second.