Efficient Drag-based Swimming using Articulated Legs with Micro Hair Arrays Inspired by a Water Beetle

Drag-based swimming is usually accompanied with the shape change of rowing appendages to generate asymmetric force during the power stroke and recovery stroke. To implement this in an aquatic robot, one may actively control the surface area of its legs during the swimming. However, a small sized robot with a limited number of actuators should adjust the surface area of legs in passive manner. For this reason, we proposed a novel articulated leg fringed with micro hair arrays inspired by a water beetle. This leg structures was especially designed to implement an efficient recovery stroke with less resistive force. By interacting with surrounding media (i.e., water), the surface area of the leg structure was adaptively increased and decreased during the power stroke and recovery stroke, respectively. Also, a 5.5 cm long swimming robot with one pair of legs was built to further investigate the performance of the leg structure. It was found from experiments that introducing a relaxation phase between the power stroke and recovery stroke not only could increase the swimming velocity, but it also reduced the number of required swimming strokes to traverse a given distance. Comparing with a non-articulated leg, a robot with articulated legs exhibited negligible backward displacement during recovery stroke.