The cownose ray (Rhinoptera bonasus) demonstrates excellent swimming capabilities; generating highly efficient thrust via flapping of dorsally flattened pectoral fins. In this paper, we present a bio-inspired and free swimming robot that mimics the swimming behavior of the cownose ray. The robot has two artificial pectoral fins to generate thrust through a twisted flapping motion. Each artificial pectoral fin consists of one ionic polymer-metal composite (IPMC) as artificial muscle in the leading edge and a passive PDMS membrane in the trailing edge. By applying voltage signal to the IPMC, the passive PDMS membrane follows the bending of IPMC with a phase delay, which leads to a twist angle on the fin. The characterization results have shown that the pectoral fin was able to generate up to 40% tip deflection and 10° twist angle with less than 1 Watt power consumption. A bio-inspired rigid body was designed using Computerized Axial Tomography (CT Scan) data of the cownose ray body and printed using a 3-dimensional printer. A light and compact on-board control unit with a lithium ion polymer battery has been developed for the free swimming robot. Experimental results have shown that the robot swam at 0.034 BL/S.
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