Unleashing the Potential of Undulating Fin Propulsion Using a Biomimetic Robotic Vessel

Abstract

AbstractUndulating fins are an excellent propulsion model for highly maneuverable underwater vehicles, due to their rich locomotor capabilities and high efficiency at moderate speed. In this study, we designed, developed, and tested a self-contained, free-swimming robotic device, the KnifeBot, to emulate the locomotor behaviors of knifefish, a typical fish that excels in using this type of propulsion. This novel biomimetic underwater vehicle uses an elongated ribbon-like fin composed of 16 fin rays interconnected by a compliant membrane as the propulsor. It features a slender 3D printed hull, 16 DC motors for actuating the fin rays, 2 Li-Ion batteries for providing power, wireless radio communication, and various sensors to measure acceleration, orientation, inside temperature, pressure and to detect leakage. We used this robotic device in two experimental sets: (1) the robot without pectoral fins to perform forward swimming, reversed swimming, and hovering maneuvers and (2) the robot with a pair of pectoral fins with fixed angle of attack (−5°) to perform forward swimming. In this paper, we focus on the design, implementation, and control of the robot. We also present the results of forward swimming velocity, power consumption, and Euler orientation angles of the robot with and without pectoral fins. Our results show that the cost of transport follows a V-shape trend with the lowest point at low swimming speed, indicating the undulating fin propulsion is more efficient at low speeds. For the cases studied, the Strouhal number, St, ranges from 0.5 to 0.2 with the best cost-of-transport corresponding to St = 0.2. We found that the airfoil-like pectoral fins at small negative angles of attack slightly slow down the speed of the robotic vessel and reduce its pitch angle. The robot can take advantage of the pectoral fins to control its maneuver from swimming at the water surface to rapid diving. Our findings demonstrate that undulating fin-based propulsion has the potential to enhance the mobility and performance of underwater vehicles navigating in complex environments.