(Harvard Microrobotics Lab/Harvard University)

Most flying animals conserve their energy by occasionally perching. Engineers would love to copy this lazy energy-saving method in drones, especially itty-bitty microbots that can't lug around heavy batteries.

These hovering little critters could be sent into dicey situations — watching wildfires, searching precarious rubble for earthquake survivors, monitoring air safety after a chemical spill — but they can't do any good if they run out of juice.

If they could perch, they wouldn't have to hover all the time. They could flit from one surface to another, making observations and collecting data while "resting" and saving energy.

In a study published Thursday in Science, researchers from Harvard University revealed a robot with perching prowess: the RoboBee.

The tiny flier was actually designed in 2013, but the addition of a clingy patch could help make it more efficient.

"A lot of different animals use perching to conserve energy," co-author Kevin Ma, a post-doc at the Harvard John A. Paulson School of Engineering and Applied Sciences and the Wyss Institute, said in a statement. "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."

Adhesives would keep the robot stuck to its perch instead of allowing it to take off again, and any kind of grasping mechanism would use up more energy than the perching saved. So instead of using glue or graspers, they created a tiny patch that can conduct electricity.

When it's turned on, it gives the robot a negative charge — a surplus of electrons. Those electrons will push the electrons on other surfaces out of the way, not unlike the way two magnets will repel one another if you try to push their northern poles together. And with those electrons pushed out of the way, the surface the robot comes up against will be positively charged — and the robot will cling to it like a balloon clings to your hair after a good rub against your sweater. Opposites always attract.

The patch has to be turned on to maintain the static cling, but it uses 1,000 times less power in perch mode than it does while flying. The mechanism weighs just 13.4 mg, bringing the robot's total weight to 100 mg. It can stick to virtually any surface, but for now it has to hang from ceilings or overhangs — the patch sits on top of the tiny drone. The team hopes to design more versatile placements for the patch in the future.

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