Development of fish-like robot with elastic fin

Purpose - Underwater robots are one of the effective solutions for underwater exploration. Fish's swimming motion is more effective and efficient than propeller screw propulsion which is more popular for underwater vehicles. So far, a lot of fish-like robots that have several actuated joints have been developed. They realize arbitrary motion by controlling the joint angles simultaneously. On the other hand, using an elastic fin may reduce the number of actuated joints and the total energy consumption. The purpose of this paper is to develop a fish-like robot driven by a single actuator with an elastic tail fin. Design/methodology/approach - Since an elastic plate appropriately bends due to the interaction to the surrounding fluid, a robot with the elastic fin can swim smoothly even though it has only a single actuated joint. However, in order to improve the swimming performances, it is required to optimize the shape of fin (width, thickness, distribution, etc.). Although computational fluid dynamics technique is one of the methods to assess the effectiveness of a certain shape of fin, it may take longer to obtain the results. Therefore, in this study, a simplified simulator is constructed and a better shape of fin is explored. Findings - Four types of fin shape were prepared and the swimming experiments were conducted. The swimming velocity changed according to the frequency and the shape of fin. In order to find the optimal shape of fin, the simulator of five-link model surrounded by fluid is constructed. The differences of velocity can be found according to the parameters of fin shape. The simulation showed the similar trend as the experiments although the absolute values of velocity did not correspond. It is thought that the developed simulator can estimate the relative performance of fins. Originality/value - Most fish robots that have been developed so far consist of rigid links and multi-actuated joints, which can realize arbitrary motion by controlling the joint angles simultaneously. On the other hand, using an elastic plate as a tail fin may reduce the number of actuated joints and the total energy consumption although it is not easy to realize arbitrary attitude. In this paper, a fish-like robot driven by a single actuator with an elastic tail fin was developed. This technique makes the mechanism of a fish-like robot simple.