From Water to Air: Design and Evaluation of a Passive Pectoral Fin Deployment Mechanism for a Flying Fish Robot

Abstract

Designing robots capable of multimodal locomotion has been an area of interest and a big challenge in the field of robotics. It presents an interesting design problem, since any system that is created to operate in a certain medium will work less efficiently when forced to operate in a different medium. However, many creatures in the natural world move between different environments very efficiently, and perform excellently in each of these environments. One such creature is the flying fish, which is capable of achieving fast speeds in the water as well as gliding up to 400m meters in the air \cite{davenport1994}. The bio-inspired adaptive morphology (BAM) lab is investigating the flying fish through the use of a robotic model organism (RMO), which can be tested in a controlled environment, and provide greater insight into the extraordinary performance of the flying fish. This project focuses specifically on the transition between water and air. When swimming, flying fish fold their pectoral fins up close to their bodies and then expand them so that they can be used as wings to glide through the air. The current RMO has a rigid wing that is unable to fold back while the fish is swimming. The goal of this project is to adapt the flying fish RMO to include a deployable pectoral fin that stays folded in the water and deploys as it propels itself out of the water. This design was then evaluated by measuring the kinematics of fin deployment and then tested in the water channel to verify whether it could still reach minimum taxi height with the added weight of the mechanism. The mechanism was able to consistently and quickly deploy the fin, however the range of motion was limited slightly by the flexibility of the materials and the waterproofing method. Additionally, the added weight of the mechanism prevented the RMO from achieving minimum taxi height. Weight is the key limiting factor and the results show that if 80g were shed from the RMO, it would be able to achieve taxi height across a full change of frequencies.