Biomimetic Realization of a Robotic Penguin Wing: Design and Thrust Characteristics

Flapping flippers or fins are widely employed in biomimetic and bioinspired aquatic robots that imitate natural swimmers, such as fish and dolphins. This article involves robotic biomimetics of the penguin, which is often overlooked as an excellent swimmer benefiting from agile wings. To achieve equivalent swimming skills in an aquatic robot, the wing motion of a real penguin was investigated. Based on the findings, we developed a three-DOF robotic penguin wing that is able to implement the same flapping, feathering, and pitch motions as in natural penguins. A kinematic analysis is presented, and the generation of swimming motions is demonstrated. We designed experiments to study the thrust characteristics of the motion of each joint. The results suggest that the flapping motion generates the main thrust during locomotion and the pitch angle can effectively change the thrust direction while the feathering motion enables active control of the angle of attack (AoA). According to the results, stalling of the wing occurs near an AoA of 10
$^{\circ }$
in the steady state; however, the feathering motion can avoid the stall and boost the net thrust by a factor of up to 7 relative to the net thrust without active feathering. Furthermore, the introduction of the feathering motion reduces the torque required to actuate the flapping motion. The hydrodynamics of the wing in different flow states are also discussed.