In a study published today in Science, researchers from Seoul University and Harvard University built an insect-like robot that mimics the way that water striders, also known as “Jesus Bugs,” jump and walk on the surface of a body of water.
The water strider is so light he rides high on the water’s surface, and it use the especially hairy feet on his middle set of legs to row his way across the water. Previously, engineers have designed striderlike robots that can walk on water, too, but they’ve never been able to duplicate the insect’s ability to jump and escape — until now.
The team collected water striders from a local pond, and used high-speed cameras to record the insects jumping on water in buckets in the laboratory. They noticed that the insects don’t simply push down on the water, but gradually accelerate their legs so as not to break the surface tension. The striders also sweep their legs inward before each jump, to maximize the amount of time they touch the surface, which increases the force of their pushes.
The new bugbot is about twice the size of a water strider and tips the scales at just 68 milligrams, a small fraction of the weight that water’s surface tension can support on an area that size. Just like its insect role model, the robot uses four legs to propel its leap from either a solid surface or from water—but it does so using the energy stored in a spring-loaded device that mimics the action of a flea’s leg when it jumps. This heat-activated spring is fine-tuned so that it pulls the bugbot’s flexible, curved-at-the-tip legs inward and downward at a speed just below that that would pierce the water’s surface, thus producing a successful leap rather than a flailing flop. A superrepellent coating on the robot’s feet and legs help prevent the water from slowing down its ascent. Although the bugbot’s body rests just 1 centimeter above the water’s surface and its legs are just 5 centimeters long, it can leap to a height of more than 14 centimeters, the researchers note. During test jumps, the robot briefly experienced accelerations of about 13.8 g—more than three times those stomached by astronauts on the space shuttle as they were boosted into orbit. Results of the new study may help engineers design bugbots that could be deployed in swarms for environmental monitoring, search and rescue operations, or the surreptitious surveillance of an enemy.