A miniature surface tension-driven robot using spatially elliptical moving legs to mimic a water strider’s locomotion

Abstract

The highly agile and efficient water-surface locomotion of the water strider has stimulated substantial interest in biomimetic research. In this paper, we propose a new miniature surface tension-driven robot inspired by the water strider. A key feature of this robot is that its actuating leg possesses an ellipse-like spatial trajectory similar to that of a water strider by using a cam-link mechanism. Simplified models are presented to discuss the leg-water interactions as well as critical conditions for a leg penetrating the water surface, and simulations are performed on the robot's dynamic properties. The final fabricated robot weighs about 3.9 g, and can freely and stably walk on water at different gaits. The maximum forward and turning speeds of the robot are measured as 16 cm s −1 and 23°/s, respectively. Furthermore, a similarity analysis with Bond number and Weber number demonstrates that the locomotion of this robot is quite analogous to that of a real water strider: the surface tension force dominates the lifting force and plays a major role in the propulsion force. This miniature surface tension-driven robot might have potential applications in many areas such as water quality monitoring and aquatic search and rescue.

Flexible Driving Mechanism Inspired Water Strider Robot Walking on Water Surface

“…For water striders, the swing range of actuating legs is 73 • , so the dimension parameter of the four-link mechanism is designed, as shown in Table 1, the corresponding swing range of the mechanism is 73 • . When compared with the former cam-link driven prototype [18], only driving legs rotates at the two extreme positions, the height and position of the driving mechanism maintain unchanged, so the new prototype consumes less power when the driving legs detach from water surface. Fig.…”

“…Scholars have carried out a lot of theoretical and experimental research on the forces acting on the legs of water striders [36]- [39]. Combine our previous work [18], the force in the axial direction F a , composed of dynamic pressure and viscosity resistance. The force in the vertical direction F v can be simplified to the sum of the lifting force corresponding to a quasi-static state and vertical velocity-induced resistance.…”

“…where V max is the critical horizontal rowing velocity before a leg pierces water surface, depending on its depth h. To make (2) solvable, referred to our previous work [18], a simple 2D model was proposed to correlate V max with the rowing velocity and depth, as is illustrated in Fig. 4.…”

“…Wu et al [16], [17] also fabricated two water strider robots powered by DC motor. Yan et al [18] designed a water walking robot with a novel cam-link mechanism to mimic the ellipse-like spatial rowing trajectory of water strider's driving leg. Up to now, the reported surface tension-driven robots generally adopted rigid wires as support legs and driving legs, utilizing the hydrophobic coatings to improve the supporting force of the robots.…”

Three-dimensional topographies of water surface dimples formed by superhydrophobic water strider legs

“…Besides those giant vehicles, along with the development of micro/nano manufacturing, the size of actuators and sensors has been significantly reduced 13,14 . Considering the exceptional capability of water-walking arthropods, there are lots of interest to explore their floating principles to establish biomimetic water-walking robots [7][8][9][10][11][12][13][14][15][16][17][18] , including their hydrophobic waxy and hairy legs to reside on water surfaces 7,19,20 and the hydrodynamic propulsions by transfer momentum through capillary waves and hemispherical vortices by sculling their legs 4,6,8 .…”