Functional design of a biomimetic flapper

Bio-inspired solutions are deeply investigated as a source of efficiency and maneuverability improvement for underwater vehicles. In the last few years, the authors of the present work have designed and manufactured a series of ostraciiform swimming robots. The necessity to pursue the highest possible propulsive efficiency in order to maximize the autonomy has driven the authors to improve their design by moving from ostraciiform to thunniform locomotion. In order to actuate the robot thruster, a transmission mechanism has been designed to convert the continuous rotation of a single motor in the harmonic roto-translation of the system output, namely the fish caudal fin. By means of this solution, inertia and encumbrance of the vehicle tail are reduced because the transmission actuator is installed on the robot rigid fore body, while waterproofing issues are minimal because a single motor needs to be sealed. Since the phase difference between the output harmonic motions of rotation and translation is maintained constant by a kinematic constraint, the effort of the control system is reduced.