Design and evaluation of a fin-based underwater propulsion system

In search of underwater locomotion methods as alternatives to propellers, systems relying on the propagation of waves along a fin have already been designed and evaluated by several scientists. Considerable effort has been undertaken to optimise their efficiency both by fluid dynamic analysis and experiments on physical prototypes. One drawback of the systems hitherto has been their electro-mechanical complexity in that they required many actuators and refined control strategies to generate the desired fin undulation. Our approach has been to translate the result of these optimisations into a simpler, purely mechanical model relying on the principle of camshafts to achieve a similar undulatory fin motion. The goal was to evaluate whether this type of propulsion system is feasible and whether it was a viable alternative to propellers in Autonomous Underwater Vehicles. The prototype built during the project, CUTTLEFIN, reached comparable speeds to other undulating robot solutions. Force measurements also showed that the thrust produced is in qualitative accordance to a simplified fluid dynamics model. This makes the camshaft approach a promising option for generating an undulating wave in a membrane-based fin propulsion system, if one is willing to pay the price of lower flexibility compared to current dexterously actuated solutions.