A RoboBee is seen next to a quarter. The static electric electrode is seen on the top of the tiny drone. (AAAS)
A RoboBee is seen next to a quarter. The static electric electrode is seen on the top of the tiny drone. (AAAS)

Tiny drones face a major problem: how to carry enough energy to keep flying for extended periods.

A team of researchers at Harvard University may have solved this problem by creating tiny drones they call RoboBees, the same weight as a honeybee - 100 milligrams - and only slightly larger. These tiny machines can conserve energe by "perching," or alighting temporarily, on pretty much any surface, just as bees and other insects flit from flit from plant to plant in nature.

Such drones would be able to perform tasks and access locations that would be impossible or dangerous for people. The researchers say potential uses include search-and-rescue work at a disaster scene, or surveillance.

"Many applications for small drones require them to stay in the air for extended periods," said Moritz Graule, the first author of the paper. He researched the problem while a student at two of Harvard's units, the John A. Paulson School of Engineering and Applied Sciences (SEAS) and the and Wyss Institute for Biologically Inspired Engineering.

"Unfortunately, smaller drones run out of energy quickly," Graule said. "We want to keep them aloft longer without requiring too much additional energy."

To come up with a way for drones to perch, the researchers looked to the insect world.

"A lot of different animals use perching to conserve energy," said Kevin Ma, a co-author. "But the methods they use to perch, like sticky adhesives or latching with talons, are inappropriate for a paperclip-size microrobot, as they either require intricate systems with moving parts or high forces for detachment."

The research team honed in on electrostatic adhesion, the same thing that “causes a static-charged sock to cling to a pants leg or a balloon to stick to a wall.”

But that static in a balloon eventually dissipates, so researchers added an electrode patch that supplies just enough energy to maintain the electrostatic adhesion.

Once the RoboBee is aloft, it can stick to almost any surface it touches - glass, wood or foliage, for example - when a charge is applied to its electrode patch. To disengage and resume flying, the electrode is turned off and the sticking stops.

"One of the biggest advantages of this system is that it doesn't cause destabilizing forces during disengagement, which is crucial for a robot as small and delicate as ours," said Graule.

For now, the electrode is attached to the top of the drone, which means it can only perch on ceilings or overhangs. Researchers say future versions will be able to perch anywhere.

"There are more challenges to making a robust, robotic landing system, but this experimental result demonstrates a very versatile solution to the problem of keeping flying microrobots operating longer without quickly draining power," Ma said.

The RoboBee could have many applications because it would be able to get to places that would be impossible or dangerous for a human.

One big potential is for surveillance since the tiny drone could fly into a room, perch quietly, collect information and then take off when the coast is clear.

Here's a video about the drone: