It’s one small jump for a water strider, one giant leap for a robot. Researchers have developed a robot inspired by how a water strider jumps on water.
To build the robot, the researchers first needed to study how the bug achieves its water-jumping feats. Remarkably, water striders are able to jump as high on water as they can on land. They typically perform this “extremely high jumping” when they are exposed to danger, though they land in a rather uncontrolled manner. Until recently, there’s been a poor understanding of the interaction between the insect’s unconstrained free body and the liquid surface.
For the study, published in the journal Science, researchers collected water striders from a local pond and used high-speed cameras to record them jumping on water in laboratory conditions. They found that the water striders’ ability to exploit the water's surface comes from their ability to gradually increase its leg force to just below the water surface’s limit. That force is maintained until the water strider disengages from the surface. Essentially, the insect is able to jump on the water as the maximum force of their legs is always just below the maximum force that the water surface tension can withstand.
Water strider jumps on water. Seoul National University
While there have been other robots inspired by the water striders’ ability to float from one place to another, there has yet to be a robot that is able to mimic their water-jumping ability – until now.
The new robot has superhydrophobic legs to make them water-repellent and a low body mass compared with the water's surface tension. The legs are also long, thin and have low-descent velocity to maximize the kinetic energy transfer to the robot instead of the water.
Robot jumps out of water. Seoul National University
Researchers used a torque reversal catapult (TRC) mechanism to allow the robot to rapidly jump a number of times. The robot also mimics another odd quirk of the water strider: "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," the researcher wrote.
The robotic design is not only cool, but it also improves our understanding of the dynamic interaction between an unconstrained free body and a liquid surface.