Abstract: In present, there are increasing interests in the research on mechanical and control system of underwater vehicles. These ongoing research efforts are motivated by more pervasive applications of such vehicles including seabed oil and gas explora-tions, scientific deep ocean surveys, military purposes, ecological and water environmental studies, and also entertainments. However, the performance of underwater vehicles with screw type propellers is not prospective in terms of its efficiency and maneuverability. The main weaknesses of this kind of propellers are the production of vortices and sudden generation of thrust forces which make the control of the position and motion difficult.
On the other hand, fishes and other aquatic animals are efficient swimmers, posses high maneuverability, are able to follow trajectories, can efficiently stabilize themselves in currents and surges, create less wakes than currently used underwater vehicle, and also have a noiseless propulsion. The fish’s locomotion mechanism is mainly controlled by its caudal fin and paired pectoral fins. They are classified into Body and/or Caudal Fin (BCF) and Median and/or paired Pectoral Fins (MPF). The study of highly efficient swimming mechanisms of fish can inspire a better underwater vehicles thruster design and its mechanism.
There are few studies on underwater vehicles or fish robots using paired pectoral fins as thruster. The work presented in this paper represents a contribution in this area covering study, design and implementation of locomotion mechanisms of paired pectoral fins in a fish robot. The performance and viability of the biomimetic method for underwater vehicles are highlighted through in-water experiment of a robotic fish.

Key words: fish robot, pectoral fins, servos, rowing, flapping, feathering