Biological inspirations, kinematics modeling, mechanism design and experiments on an undulating robotic fin inspired by Gymnarchus niloticus

This paper suggests and then presents a whole procedure of biomimetics with a case study starting from amiiform fish (Gymnarchus niloticus) to an undulating robotic fin. The procedure includes biological observation, kinematics modeling, mechanism design, prototype implementation, and initial experiments. To investigate undulatory median fin propulsion and its potential for applications in man-made underwater vehicles, a motor-driven fin actuator, RoboGnilos, has been developed with inspirations from G. niloticus, which generally swims by undulations of a long flexible dorsal fin. In the kinematics modeling, the ruled surface based model is proposed to describe the undulation characteristics and used as a guide for the biomimetic mechanism design and implementation. Next, a modular independent motor-driven mechanism is adopted to implement the undulating prototype fin by virtue of reconfigurable features. Finally, initial experiments have been carried out to analyse how undulation dynamics is affected with the morphological parameters (i.e., the asymmetry of waveforms, the fin surface material, and the fin ray length) and the undulatory parameters (in terms of the wave length, the amplitude, and the undulation frequency). The kinematics simulation presented in this paper shows that the proposed ruled surface model can better describe and fit more undulation characteristics than other models. And the experiments verify that the design of the modular motor-driven mechanism is convenient and effective.