The concept of walking on water might sound supernatural, but in fact it is a quite natural phenomenon. Many small living creatures leverage water’s surface tension to maneuver themselves around. One of the most complex maneuvers, jumping on water, is achieved by a species of semi-aquatic insects called water striders that not only skim along water’s surface but also generate enough upward thrust with their legs to launch themselves airborne from it.
Now, emulating this natural form of water-based locomotion, an international team of 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, has unveiled a novel robotic insect that can jump off of water’s surface.
In doing so, they have revealed new insights into the natural mechanics that allow water striders to jump from rigid ground or fluid water with the same amount of power and height. The work is reported in the July 31 issue of Science.
The water strider, whose legs have slightly curved tips, employs a rotational leg movement to aid it its takeoff from the water’s surface. Researchers take extensive videos of the water striders movements to analyze the mechanics that enable the insects to skim on and jump off water’s surface.
It took the team several trial and error attempts to fully understand the mechanics of the water strider, using robotic prototypes to test and shape their hypotheses.
But by studying water striders in comparison to iterative prototypes of their robotic insect, they have 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.
Mimicking these mechanics, the robotic insect built by the team 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.
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 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. 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.”
“This international collaboration of biologists and roboticists has not only looked into nature to develop a novel, semi–aquatic bioinspired robot that performs a new extreme form of robotic locomotion, but has also provided us with new insights on the natural mechanics at play in water striders,” said Wyss Institute Founding Director Donald Ingber.
