Researchers from South Korea have created a robotic insect that’s capable of jumping and landing on an aquatic surface, a unique mode of transportation found only in specialized animals.
To reproduce this jumping ability in a robot, Je-Sung Koh and colleagues from Seoul National University studied the way water striders do it. The resulting bio-inspired robots demonstrate that this extraordinary insectoid capability can be replicated in an artificial system. The results of this team’s work now appears in the latest edition of Science.
Water striders, a semi-aquatic arthropod, are specially evolved for the task. They feature an exceptionally low body mass and superhydrophobic, i.e. water repelling, legs. What’s more, water striders support themselves on their trasi—the center segment of their foot—by surface tension alone. When making their dramatic leaps, these insects can generate enough vertical force to jump from the water surface, which is an action that typically requires high momentum.
A water strider doing what it does best (Credit: Seoul National University)
By analyzing high-speed images, the researchers discovered that water striders rotate the curved tips of their legs inward with a force just below that which is required to break the water surface. The authors determined this degree of force — exactly 144 milli-Newtons/meter—by using a theoretical model of a flexible cylinder floating on liquid.
Also, the researchers observed that the water strider’s long legs accelerate gradually such that the water surface doesn’t retreat too quickly and lose contact with the legs. Remarkably, water striders can jump on water as high was when they jump on ground.
Water strider together with a robotic insect that can jump on water. (Credit: Seoul National University)
Armed with this knowledge, the researchers set about the task of creating a robotic analogue. The resulting at-scale jumping robot, which weighs in at a mere 68-milligrams, perfectly recreates the controlled acceleration of their biological counterparts. The researchers used a “torque reversal catapult” mechanism to produce the required small burst of initial torque.
“What was very important for us while building the jumping water robot was to make sure that the maximum force does not exceed the maximum surface tension force,” noted Je-Sung Koh in an accompanying video demonstration.
And like the water strider, the robotic insect maximizes its overall lift off force by sweeping its legs inward to maximize the time its legs can push against the surface of the water.
Thus, by combining all these critical factors—light weight, long limbs, and similar physical mechanisms—the researchers were able to create their robotic water strider.
Read the entire study at Science: “Jumping on water: Surface tension-dominated jumping of water striders and robotic insects”.