The Effect of Design and Control Parameters of a Soft Robotic Fish Tail to Maximize Propulsion Force in Undulatory Actuation

Abstract

A tetherless underwater soft robot inspired by the capabilities of biological fish is an ideal tool to navigate complex underwater environments. Such a robot could take dense three-dimensional sensor readings for a better understanding of the ocean's changing microclimates, while not disturbing the natural underwater life. This paper presents a soft 3D-printed cable-driven flexible fish tail and studies the design and control parameters to maximize its thrust force output for use on a soft robotic fish. The parameters tested were caudal fin shape, fin area, fin thickness, frequency, length of cable retraction, and input waveform. Our results indicate that a 6 in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (38.71 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), 2 mm thick trapezoidal tail provides the maximum mean force output with all tested input waveforms. The optimal motor parameters were a triangular input wave with a cable retraction of 16.76 mm operating at 1.67 Hz. Based on our results, using simple driving waveforms with cable driven caudal fins will pave the way towards efficient tetherless exploration and monitoring tasks in complex underwater environments such as coral reefs.