Inspired by nature - a robotic water strider next to its real-life counterpart

Water-strider inspired robot can leap from water surface

A robot can walk on and launch itself from water surface by mimicking abilities of water striders. 

The tiny robotic creature, described in the latest issue of the journal Science, was created by a team of researchers from South Korea’s Seoul National University and Harvard University, the USA.

The researchers first studied the motion of water striders, tiny insects with long thin legs that can be commonly seen sliding on water surfaces of every pond or lake.

Among the amazing abilities of water strides is the fact that they can launch themselves from the water surface with the same ease as from the firm ground.

Using high-speed cameras to understand how exactly the simple beetles do their tricks, the researchers discovered that the long legs of the water strider accelerate gradually as it launches itself upwards, so that the water surface doesn't retreat too quickly and lose contact with the legs. Moreover, the water striders' legs have slightly curved tips that rotate inwards before the take-off, which allows them to maximise the time they stay in contact with the water surface.

"Water's surface needs to be pressed at the right speed for an adequate amount of time, up to a certain depth, in order to achieve jumping," said Kyu Jin Cho, Associate Professor in the Department of Mechanical and Aerospace Engineering and Director of the Biorobotics Laboratory at Seoul National University. "The water strider is capable of doing all these things flawlessly."

Subsequently, the team tried to emulate what they saw. They built a body of the robotic water strider using the so-called pop-up manufacturing, a folding process for rapid fabrication of micro-robots and electromechanical devices.

The actual launch mechanism of the robot used a method inspired by flea jumps that allows extreme locomotion without intelligent control. The mechanism employed to launch the robot from the water surface, dubbed the torque reversal catapult, gradually increases the torque to make sure it never exceeds the surface tension force of water.

"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 Robert Wood from the Harvard Paulson School.

The researchers envisage the robotic water striders could be used, for example, to monitor pollution of waterways. In the more distant future, they could perhaps lead to the creation of more agile amphibious robots capable of swiftly switching between the water environment and air.

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