Surface Tension-Driven Biologically Inspired Water Strider Robot

Humanbeings mainly live on land, and have less knowledge of some rural water areas due to the limited detection capabilities. Aquatic devices and robots can extend the scope of mankind’s activities, and help explore unknown water areas. Nowdays, miniaturization technique and multi-robot system are popular research fields due to their own special features. Mini/micro water strider robots can walk on water with small resistance to motion and little disturbance in water, resulting in low noise and high efficiency, which possesses a surface tension-dominated locomotion, enabling it with agile motion capability even in shallow water regions. In future, if a certain number of water strider robots together with a base station are arranged in an objective water area, then they can help carry out various tasks such as water quality monitoring, aquatic search and rescue. What’s more, the study of water strider robots refers to several subjects such as bionics, MEMS, advanced materials, robotics and hydrodynamics, so relavent research also can promote the developments of several research fields, which is of great scientific importance.Unique structure configuration and stroke mechanics enable water strider with quick, agile and high-efficiency water-surface locomotion, which is of great rationality and scientificity. In this thesis, according to the underlying mechanisms of superhydrophobicity and water-surface locomotion of water strider, the biological principles of surface tension-driven mode are discussed; the wettabilicy, dynamic wetting of rough surfaces and air-water interface related hydrodynamics are theoretically studied; a novel miniature surface tension-driven robot is proposed to mimic water strider’s skating motion on water.According to scale effects and surfae tension-related dimensionless parameters, the role of surface tension force played in the water-surface motion of some miniature aquatic insects is analyzed. The biological principles of surface tension-driven mode and the rationality of water strider’s water-surface locomotion are discussed. Then the basic idea and significance of the biomimetic research are addressed.Based on wetting theory and minimum interfacial free energy principle, analysis models of contact angle hysteresis phenomenon and hydropressure-induced failure of supperhydrophobicity of rough surfaces are built from the aspect of moving three phase contact line, which are verified via experiments and MD simulaitons, respectively. Then dynamic wetting properties of copper-based supperhydrophobic material we prepared in this study are analyzed, which are used to calculate the load capacity and rowing frequency of water strider robot, and analyze the stability of the robot’s water-surface motion.A model of multi-cylinder system contacting with water is built and the effects of wettability, structure and positon on the cylinder-leg interactions are discussed, the results of which can be used to help design the robot’s supporting system and analyze load capacity. A model of critical condition for a leg penetrating water surface when horizontally rowing is built, and a new dimensionless number is proposed to decide wether a leg piercing water or not. Relevant study is helpful for the dynamic analysis of water strider robots.On the basis of water-surface locomotion of water strider, three basic design principles are proposed. Then structural design of the miniature surface tension-driven robot is implemented, including shape design and strength check of supporting and actuating legs, and design of a novel cam-link mechanism to mimic the ellipse-like spatial rowing trajectory of water strider’s middle leg. Based on the model of multi-cylinder system contacting with water, the supporting system of the robot is designed with its load capacity on water being calculated.According to the theoretical model of long-and-thin cylinder interacting with water, a model for the analysis of the stability of water strider’s water-surface motion is proposed. A mass-spring-damping like model is adopted to describe the robot-water interactions, in terms of which the effects of actuating legs’ rowing and installation position on the robot’s stability are investigated. Then a dynamic model is built and simulations are performed on the robot’s dynamic properties by using software ADAMS.Finally, a robot prototype is fabricated with a PWM-based controlling system. Experiments are carried out to observe the actions and trajectory of the actuating leg. The dynamic properties of the robot moving on water are tested as well, and are compared with simulation results to verify the validity of the dynamic simulation method. Then, the superiority of this spatially elliptical motion mode over two-dimensional motion modes is demonstrated from the aspects of stability on water and energy consumption for a leg detaching from water. At last, two dimensionless parameters are employed to discuss the locomotion similarity between this novel robot and water strider.