Engineers have invented tiny drones that use the power of static cling to attach themselves under almost any surface — wood, glass and even leaves.

That could enable them to observe an area from a high vantage point while consuming almost no power, allowing them to work for much longer before recharging their batteries.

Flying "microbots" like the RoboBee, invented by researchers at Harvard University, have a lot of advantages over bigger drones, says Robert Wood, an engineering professor at the university's John A. Paulson School of Engineering and Applied Sciences.

"They're agile, they can fit into small nooks and crannies, you can have a lot of them operating simultaneously to have greater coverage," he said in a video explaining the new development, "but the drawback is they're very inefficient at flying."

Because of that, drones weighing less than two kilograms can't usually fly longer than an hour.

Flying animals such as birds, bats, bees and butterflies conserve energy by stopping and perching from time to time. But the way they do it, by latching on to things with feet and claws, for example, is difficult to apply to drones.

Rodrigue fruit bat

A Rodrigues fruit bat hangs on a perch in the Masoala rainforest hall at the zoo in Zurich. Flying animals such as birds, bats, bees and butterflies conserve energy by stopping and perching from time to time. But the way they do it, by latching on to things with feet and claws, for example, is difficult to apply to drones. (Arnd Wiegmann/Reuters)

Previous perching robots developed by scientists and engineers have used spines to stick to certain kinds of surfaces or magnets to attach to certain metals. That limits the kinds of places they can attach to, and may make it difficult for the robot to take off again.

Woods and his team came up with a different approach — they equipped the RoboBee with an electrode patch that allows it to use static electricity to stick to surfaces, the way a balloon sticks to a wall after you rub it on your hair.

A foam patch keeps it from bouncing off the surface as it attaches. Detaching is simple — the robot just cuts power to the electrode so it no longer sticks.

"The low disengagement forces are really important because they enable future prototypes of the robot to land somewhere and not only stay there and use the high vantage point for observation, but also to reposition itself and return to an operator with collected data," said Moritz Alexander Graule, first author of a study describing the research, which was published in Science today.

The RoboBee has a wingspan of just 36 millimetres and weighs less than 100 milligrams including the patch — about the mass of a small bumblebee. In order to generate enough static electricity to stick to a surface, it uses just a thousandth of the energy required to hover for the same length of time.

At the moment, the patch is attached to the top of the RoboBee, so it can only land and perch on ceilings and under overhangs, like a bat.

But the team is working on a design that will allow future versions to perch on any surface.