# Jumping Locomotion Strategies: From Animals to Bioinspired Robots
## 2 Jumping Animals and Biomimetic Miniature Jumping Robots
### Specialized Jumping Performance: Aquatic Environments
#### 2.3.1 Water-Strider Inspired Jumping Robots  
Water-strider is one kind of small insect commonly found in lakes, ponds, paddy fields, and wetlands. It can walk, glide, and jump on water surface. Researchers have conducted thoroughly studies on the floating and locomotion mechanism of water-strider. The results show that the agile locomotion ability of water-strider on the water surface is mainly due to the superhydrophobicity [191; 192] of its own leg structure, capable to provide enough surface tension. Water-strider can increase the support force by increasing the depth of the leg into the water [179]. By moving their superhydrophobic hind and middle legs inward at a relatively low descending velocity, water striders can generate a force that is below the value required to break the water surface and initiate jumping [179].  
Researchers from Seoul National University and Harvard University collaboratively developed a microscale water strider-inspired skating robot [193] and another jumping robot based on SMA and bistable click mechanism [194] that, in its latest version [179], has a mass of only 68 mg and astonishing performances: 1.6 m/s take-off velocity, 142 mm jumping height. The size of the robot, the locomotion mechanism, and the trend of the contact force during take-off are very similar towater-strider [179]. At the same time, researchers used a high-speed camera to study the jumping mechanism of water-strider. Recordings were used to establish a mathematical model that allows to calculate the support force during take-off. It was found that water-strider can get maximum momentum by moving the four legs, without destroying the water surface.  
[PERSON] et al. [191; 192] analyzed the microscopic mechanism of superhydrophobic materials and the locomotion mechanism of the water-strider, which lays a foundation for the development of the subsequent water-strider walking robots [195] and jumping robots [196; 197]. Their water-strider-inspired jumping robot [196; 197] combines support legs and propulsive legs. This is achieved by means of a click mechanism using incomplete gears. Through simulations and experiments, the effects of the foot area, spring stiffness, and take-off angle on the take-off performance of the robot have been studied. The robot can make use of the buoyancy achieved by superhydrophobic nickel foam materials, that, among others, reduce energy consumption. The possibility of applying water strider-inspired robots to water quality surveillance and water pollution monitoring is also mentioned [195].  
[PERSON] et al. [198] developed a water-strider-inspired jumping robot that uses incomplete gears and ropes to drive a carbon fiber elastic band. It can realize jumping by rapid kicking of feet. The minimum body weight of the robot is achieved by optimization of the mechanism and the jumping performance is predicted based on a general and simplified mathematical model proposed. In the experiments, the jumping height is less than the robot leg's length. An integrated optimization combining the mechanism optimization and the jumping modelling is required to improve the jumping performance in the future.