Walking on water

A researcher at Carnegie Mellon University in Pennsylvania has built a tiny robot that can walk back and forth on water, much like insects known as water skimmers.

Rather than floating, the device supports itself on top of the liquid as it is not heavy enough to break the water’s surface tension. ‘I think it is the final challenge of microrobotics if you can make this thing,’ said assistant professor of mechanical engineering Metin Sitti, creator of the device. ‘It needs to be so light and compact.’

The development builds on research from MIT last year that discovered how water insects move across a frictionless surface. The team found they did this by pushing down on the water’s surface. As this bounces back, they are propelled forward.

Sitti said that, with the addition of a chemical sensor, his water-skimming robot could monitor water supplies for contamination or other toxins. With a camera it could be used as a ‘spy’ or an explorer and with a net or boom it could skim off contaminants.

The device weighs about 1g and is just over 1cm long. It consists of a carbon-fibre body with eight 5cm-long legs that are made from steel wire coated with a water-repelling plastic. It has no battery or sensors, but moves using two legs that act like oars.

Its leg muscles consist of three piezoelectric actuators, pieces of metal that change shape when electric current is run through them. The actuators are attached to wires and controlled by three circuits connected to a power supply. So far it is cheap to make, costing around $10 (£5).