Researchers in Korea have developed a robot that can mimic water striders, with the bioinspired long-legged bot leaping across water thanks to a very clever design.
By looking at the technique water striders use when leaping across lakes, Je-Sung Koh and his colleagues in the Seoul National University developed a weird-looking device that utilised something called a torque reversal catapult (TRC).
This mechanism initially generates a small amount of torque and gradually increases, careful not to exceed the surface tension force of the water, which is key as it means water is more receptive to the leaping motion.
By looking closely, the researchers spotted that this tactic – of always staying just below the surface tension limit – was integral to water striders and thus designed legs and movements to replicate this.
“What was very important for us while making the water-jumping robot was to make sure the maximum force did not exceed the maximum surface station force,” explained Kyu-Jin Cho, one of the authors of the paper published in Science.
Cho and his team spotted that water striders rotate their legs to maximise the interaction time between the legs and the water, which means there’s more time and interaction to transfer momentum.
“What we devised was a very small bioinspired jumping mechanism called a TRC, which applies small force initially. The force increases gradually so we can maximise the momentum transfer without exceeding the maximum surface tension force.”
So they developed a tiny robot with 5cm legs and a 2cm body, similar to a water strider’s shape, but around twice the size.
The legs are curved towards the end to allow for the rotation, with a “super repellent coating” helping to prevent the ascent from slowing.
“During test jumps, the robot briefly experienced accelerations of about 13.8g — more than three times those stomached by astronauts on the space shuttle as they were boosted into orbit,” according to Science.
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