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#Future Tech

Researchers take cue from nature to develop robot that mimics water striders

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Water striders are probably one of the most fascinating insects for their ability to ‘walk’ on water and taking a cue from them, an international team of researchers has developed a robot that can jump off water’s surface.

Scientists from Seoul National University, Korea (SNU), Harvard’s Wyss Institute for Biologically Inspired Engineering, and the Harvard John A. Paulson School of Engineering and Applied Sciences found out the reason why water striders can not only skim but also generate enough upward thrust with their legs to launch themselves airborne from it.

The key, researchers say, is their legs with slightly curved tips as well as the method of applying force to generate the necessary upward thrust. By studying water striders in comparison to iterative prototypes of their robotic insect, the SNU and Harvard team discovered that the best way to jump off of water is to maintain leg contact on the water for as long as possible during the jump motion.

“If you apply as much force as quickly as possible on water, the limbs will break through the surface and you won’t get anywhere,” said Robert Wood, Ph.D., who is a co-author on the study, a Wyss Institute Core Faculty member, the Charles River Professor of Engineering and Applied Sciences at the Harvard Paulson School, and founder of the Harvard Microrobotics Lab.

“Using its legs to push down on water, the natural water strider exerts the maximum amount of force just below the threshold that would break the water’s surface,” said the study’s co-first author Je-Sung Koh, Ph.D., who was pursuing his doctoral degree at SNU during the majority of this research and is now a Postdoctoral Fellow at the Wyss Institute and the Harvard Paulson School.

Researchers built their robot such that it mimics these mechanics and the result is that it can exert up to 16 times its own body weight on the water’s surface without breaking through, and can do so without complicated controls. Many natural organisms such as the water strider can perform extreme styles of locomotion – such as flying, floating, swimming, or jumping on water – with great ease despite a lack of complex cognitive skills.

“This is due to their natural morphology,” said Cho. “It is a form of embodied or physical intelligence, and we can learn from this kind of physical intelligence to build robots that are similarly capable of performing extreme maneuvers without highly-complex controls or artificial intelligence.”

In this video, watch how novel robotic insects developed by a team of Seoul National University and Harvard scientists can jump directly off water's surface. The robots emulate the natural locomotion of water strider insects, which skim on and jump off the surface of water. For more information, please visit: http://wyss.harvard.edu/viewpressrelease/210/

The robotic insect was built using a “torque reversal catapult mechanism” inspired by the way a flea jumps, which allows this kind of extreme locomotion without intelligent control. It was first reported by Cho, Wood and Koh in 2013 in the International Conference on Intelligent Robots and Systems.

For the robotic insect to jump off water, the lightweight catapult mechanism uses a burst of momentum coupled with limited thrust to propel the robot off the water without breaking the water’s surface. An automatic triggering mechanism, built from composite materials and actuators, was employed to activate the catapult.

To produce the body of the robotic insect, “pop-up” manufacturing was used to create folded composite structures that self-assemble much like the foldable components that “pop-up” in 3D books. Devised by engineers at the Harvard Paulson School and the Wyss Institute, this ingenious layering and folding process enables the rapid fabrication of microrobots and a broad range of electromechanical devices.

“The resulting robotic insects can achieve the same momentum and height that could be generated during a rapid jump on firm ground – but instead can do so on water – by spreading out the jumping thrust over a longer amount of time and in sustaining prolonged contact with the water’s surface,” said Wood.