Design of a bioinspired ray robot with flexible fins

Abstract

This paper presents the design and construction of a biomimetic swimming robot inspired by the locomotion of rays. These fishes move by flapping their pectoral fins and creating a wave that moves in the opposite direction to the direction of motion, pushing the water back and giving the fish a propulsive force due to momentum conservation. The robot's fins are molded from silicone rubber and moved by a servo motor that drives a mechanism inside the leading edge of each fin. The traveling wave, mimicking the movement of the fin, is passively generated by the flexibility of the rubber itself. The robot is also equipped with a tail that acts as a rudder, helpful in performing maneuvers. The rigid central body of the robot is the housing for motors, electronics, and batteries.

Development of an underwater robot with undulation propulsion

“…The robot is neutrally buoyant, and its mass is balanced by adding ballasts. 32 The robot's central body houses the electronic components, so it is entirely waterproof and composed of a waterproof box, with dimensions 80mm x 150mm x 60mm, and two 3D-printed extensions attached. There LiPo batteries (Grepow GRP6134060) placed at the bottom of the box are connected in series, and their nominal voltage is 3.7V; their capacity is 1200 mAh, and the discharge rate is 15C.…”

“…The pectoral fins of the robot reproduce as accurately as possible the shape of a cownose ray's fins whose contour has been taken from the literature, 15,33 and it has been scaled to the actual chord length of the robot. 32 The cross-section of the fin is a biomimetic profile thicker near the leading edge, thinner in the rear part, and almost flat at the trailing edge since a fin with this shape produces considerably more propulsive force than a fin shaped like a NACA profile. 34 The fin is made of silicone rubber, and the leading edge is made stiffer by adding an aluminum rod mounted on the motor bracket.…”

“…The fins are manufactured by pouring liquid silicone rubber inside 3D-printed molds. 32 The stiffness of the fin is tuned to have the first natural frequency at about 1Hz, in the frequency range where large amplitude movement is feasible with the selected motors. Then, the frequency response of the fin is evaluated in two steps: first, a linearized frequency analysis is performed to get an approximate value of the first natural frequency, then some dynamic simulations are carried out.…”

“…Thus, the selected motors can move the fins at the resonance frequency with a peak-to-peak amplitude of more than 90°. 32…”