Design of hair-like appendages and their coordination inspired by water beetles for steady swimming on the water surface

Locomotion of water beetles have been widely studied in biology owing to their remarkable swimming skills. Here, we investigated the coordination between the two pairs of legs to achieve steady swimming with novel hair-like appendages. Some design considerations and a fabrication of the hair-like appendages, which can passively adjust their projected area to obtain net thrust, are proposed. As do water beetles in nature, the coordination between the two pairs of legs were considered to achieve steady swimming without jerky motion by varying the beating frequency and phase of the legs. To verify the functionality of the hair-like appendages and their coordinations, six different types of appendages were fabricated, and two robots (one with single pair and the other with two pairs of legs) were built. Locomotion of the robots were compared through experiments, and steady swimming was achievable by properly coordinating the two-pairs of legs without sacrificing the swmming speed.