Kai Yang

Water jumping motion extends the robot's movement space and flexibility. However, the jumping performance is influenced by multiple factors such as driving force, rowing trajectory and robot structure. The interaction force between the robot and water surface is complicated due to water deformation, and the difficulty of the water jumping increases with the robot's scale. This paper designs a miniature water jumping robot with rowing driving legs. The hydrodynamic model between driving legs and water is established based on the modified Wagner theory with consideration of water surface deformation. Particularly, the dynamic model of the robot for the whole jumping process is also developed relate to multiple factors. Then the jumping performance is improved by optimizing the energy storage modality, rowing trajectory and supporting leg shapes through the theoretical analysis and experiments. The fabricated robot weights 91 g, and its length, width and height are 220 mm, 410 mm and 95 mm respectively. The maximum water jumping height and distance are 241 and 965 mm.

Water striders slide agilely and quickly on the water surface with the spatial elliptical rowing trajectory, it has attracted the research interest of scholars. But the existing bionic robots did not realize the level of it and generally suffer from slow speed and weak load capacity. Inspired by the trajectory of the water strider, the influence of its shape, size and velocity to the robot speed was analyzed by the numerical method. Based on the optimization parameters, the dexterous driving mechanism with a single motor is designed to achieve the spatial elliptical rowing trajectory within the restricted size and weight. The robot is manufactured with a mass and load capacity of 863 g and 600 g, respectively. The experiment of the sliding motion on the water was carried out. Its forward and turning speed are 625 mm/s and 45 °/s respectively, and the speed/body length ratio is higher than the other similar robots. It also has been verified that the robot can slide in the disturbance environment with wind speed of 2.3 m/s and wave height of 210 mm.

The agile and efficient locomotion of water striders on water surface is attributed to the water repellency ability of their slender legs. The legs are usually treated as rigid beams, neglecting the effect of flexible deformation on its movement. Several studies proved that the stable floating ability of water striders is closely related to the flexible legs. This paper focuses on exploring the flexible driven mechanism between the insect and the surface of water and applied them to design a robot. The spatial deformation and force models of the driving legs are established and analyzed based on the Euler-Bernoulli’s beam theory. The influence of flexural rigidity and depth of a driving leg on the rowing speed is studied. Results indicates that a flexible driving leg can effectively increase its critical rowing speed and ensure that it does not penetrate the water surface at a higher speed, thus achieving a bigger driving force. Then a water strider robot capable of walking on water surface is proposed, which possesses ellipse-like spatial trajectories by using a limit pin-linkage. The driving legs are fabricated by different stiffness materials. Finally, the skating experiments of the robots with different stiffness of the driving legs were carried out. The results verified that the maximum rowing frequency of the flexible driving legs and maximum moving speed of the robot are more than 30% higher than those with rigid legs, respectively. Moreover, a similarity analysis of hydrodynamic characteristic constants reveals that the flexible driving robot is more analogous to the biological water striders.