Design and Development of a Bio-inspired Pectoral Fin for an Underwater Robot

In this thesis the design, development and testing of a novel bio-inspired pectoral fin is presented and its possible applications are discussed. The fin was designed with a soft robotic approach, using SMA wires as tendon actuators and a body made of silicone, allowing to obtain a lightweight actuator, weighing approximately 47g, capable of producing forward thrust. The design was based on the paddle shaped fins of labriform swimmers, with possibility to independently move two rays placed in the extremities of the fin to perform different swimming patterns. The rays allowed a basic position control thanks to the presence of embedded flex-sensors, which was used to control the rays’ movement during the outstroke of the beat-cycle. A dedicated electronic circuit was designed in order to drive the actuator. The fin was tested in water with two different swimming mechanisms: a sinusoidal wave propagation, to produce vertical forces and a rowing motion, to produce forward thrust. The results of the sinusoidal motion were unsatisfactory due to the low precision of the movement obtained and the asymmetries of the fin. On the other hand, the rowing motion allowed to produce an average forward thrust of 0.0145 N with a beat-cycle frequency of 4s. The experiments evidenced the possibility to change the frequency and amplitude of the movement in order to change the magnitude of the produced force.