Jumping on water: Surface tension–dominated jumping of water striders and robotic insects

Abstract

Jumping on water is a unique locomotion mode found in semi-aquatic arthropods, such as water striders. To reproduce this feat in a surface tension-dominant jumping robot, we elucidated the hydrodynamics involved and applied them to develop a bio-inspired impulsive mechanism that maximizes momentum transfer to water. We found that water striders rotate the curved tips of their legs inward at a relatively low descending velocity with a force just below that required to break the water surface (144 millinewtons/meter). We built a 68-milligram at-scale jumping robotic insect and verified that it jumps on water with maximum momentum transfer. The results suggest an understanding of the hydrodynamic phenomena used by semi-aquatic arthropods during water jumping and prescribe a method for reproducing these capabilities in artificial systems.

Measurements of milli-Newton surface tension forces with tilted fiber Bragg gratings

“…Once calibrated, a TFBG can be used to measure unknown forces in the same range or to measure an unknown ST, provided a separate force measurement is available. Liquid molecules situated near or at the interface (i.e., liquidgas or liquid-solid) have different spatial orientations with respect to each other, compared to the molecules in the bulk phase [1][2][3][4]. The intermolecular attraction forces acting on each molecule in the bulk liquid phase are isotropic at a fixed temperature, and this means that the resultant force in any direction is balanced.…”

Re-engineering artificial muscle with microhydraulics

“…Significant advances have recently been made in realizing autonomous microsystems, from micro-sized aerial vehicles (μUAVs) 1 , to jumping robots 2 , and even to magnetically controlled systems that can navigate inside the human body 3 . However, there seem to be almost as many modalities for microsystem actuation as there are examples of microsystems.…”

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

“…3. The shadow images, supporting forces F n acted on individual legs, the whole supporting forces, and the whole lateral propulsive force calculated 24 based on the hydrodynamic force and the surface tension force from the anisotropic shadow (see Methods) have also been achieved as shown in Fig. 3 b&d. During sculling forward of a water strider (33.1mg), assuming a rigid connection of its fore and hind legs with body, the shadows of legs S1, S2, S4 and S5, and the corresponding pitch angle (See methods) of its body of about  3 as shown in Fig.…”

“…An ex vivo measurement with electronic balance showed that the maximum supporting force of one water strider leg could be up to 152 dynes (1 dyn = 10 N), several times of its body weight 7 . A recent study showed some force estimations of the jumping upward of water striders and robotic insects 24 .…”

“…Weak forces in nN to N in ambient environment are usually achieved with atomic force microscopy (AFM) [21][22][23] , which could not be used for live water striders. Another way is to measuring forces acted on legs according to Archimedes' principle, the weight of the volume of water repelled by a floating object is equal to its own weight 5,24,25 . An ex vivo measurement with electronic balance showed that the maximum supporting force of one water strider leg could be up to 152 dynes (1 dyn = 10 N), several times of its body weight 7 .…”