Robot can leap from water's surface

Scientists have developed a tiny robot - based on the water strider insect - that can jump on water.

The robotic version uses the same forces to jump as the water strider - pushing off without breaking the surface.

It takes off with a downward force that never exceeds the surface tension of water - the force that "glues" surface water molecules together.

The robots use the same jumping technique as the insects that inspired their design. Photo: BBC

The South Korea and US team's advance is reported in the journal Science.

Lead researchers Prof Ho-Young Kim and Prof Kyu-Jin Cho, from Seoul National University, used water striders from their local pond in the study.

"To explore [their] amazing semi-aquatic motility, we collected [the insects] and recorded them jumping on water in the laboratory with high-speed cameras," the scientists said.

"[These imaging experiments] revealed that the insect rises upward while pushing the water surface downward and closing four of its legs inward."

So the team set out to build that motion into the design of their robot.

Each robot's 2cm (0.8in) body is made of layers of thin material folded into a vee-shape, with a spring running across its length.

When powered up for a jump, the spring releases, but slowly, dragging the ends of robot's body and its 5cm insect-like legs downward with gradually increasing force to the limit the water surface will withstand.

The robot's legs never break the water surface. Photo: BBC

The robots - and the insects - also rotate their legs inward "to maximise the interaction time between the legs and the water".

The researchers envisage an environmental application for their robotic water strider - monitoring pollution in waterways.

But they added their goal had been not to commercialise their miniature robot, but to explore "a new possibility [for] a robot's aquatic mobility".