Flying can be exhausting when you’re a tiny, bee-sized robot, but researchers from Harvard have created a new way to let little winged bots take a break. Using static electricity, robots no bigger than a quarter can latch onto the underside of any flat surfaces, a process that uses between 500 and 1,000 times less power than flying. In a study published in this week’s issue of Science, researchers say this new perching ability could be key to creating insect-sized aerial robots that can help with a long-term observational tasks — traffic control, to search-and-rescue.

the robobee is 31 times lighter than a penny

The mechanism was developed by researchers from Harvard for the RoboBee: a tiny flying robot first unveiled by a team from the university in 2013. The RoboBee weighs just 0.08 grams (that’s 31 times lighter than a penny), and has a pair of tiny wings that can beat up to 120 times per second. Previously, the bot relied on miniature tripod on its base for landings — but that meant it could only set down on the top of flat surfaces. The new mechanism will instead let it fix onto the underside of pretty much any material, including leaves, glass, wood, and brick.

A partial swarm of Robobees at rest. (Image credit: Wyss Institute)

Perching isn’t a trivial skill, either. It could be vital to create small robots designed for medium and long-term observations. You can’t use a quadcopter to survey an area for longer than 20 or so minutes, for example, as it simply runs out of power. But if a robot (even a tiny one) can perch somewhere without using much energy, it can stick around for longer. Mirko Kovac, an aerial roboticist who wrote an accompanying essay in the same issue of Science, suggests that if scientists can incorporate renewable energy sources into their designs (like solar panels), then a robot could literally recharge its batteries while taking five on branch.

monitoring everything from rain forests to traffic jams

"This incredibly important for inspection tasks," says Kovac. "Industrial inspection, for example, or environmental monitoring, like in the rainforest. Another one would be traffic control. There are many different applications, but it always comes back to the benefits of using much less energy."

The electrostatic pad itself sits on the top of the RoboBee, making it look a little like a rubber dart, and is connected to the bot via a polyurethane mount that’s essentially a squidgy ear plug. This allows the circular contact to bend and flex, meaning the microrobot can approach its target surface at an angle, rather than having to line exactly parallel.

The static electricity that is used to stick the bot to its target is the same force that makes a balloon attract your hair after you’ve rubbed it on a sweater. An electric current is run through the circular pad to create the charge, and when it touches the target surface, it induces the opposite charge there, creating electrostatic attraction between the two materials. Voila: the robot sticks in place.

An illustration of how the Robobee attaches to a target surface. The circular pad is the electrostatic mechanism and the yellow cylinder is the polyurethane mount. (Image credit: Science)

This might seem like an unnecessarily complex mechanism to use, but it’s ideal for a bot the size of the RoboBee. Because the electrostatic attraction can be turned on and off, the robot doesn’t need to pull itself away from any surface, as it might with a chemical adhesive. (Just think of flies stuck in fly paper!) Maintaining the charge also takes very little power — 500 to 1,000 times less power than flying.

In his essay, Kovac describes how animals of different sizes use different methods to perch, and how the same lessons can be applied to robot design. Large birds have to use visual feedback and the precise deployment of talons to grip on to something, writes Kovac, while smaller insects like flies, meanwhile, simply run into something and the design of their bodies allows them to stick in place. (In the case of flies, this "stickiness" comes from a huge number of tiny bristles on their feet that work like velcro.)

"Nature is very good at this sort of embodied intelligence."

You can’t scale down mechanical grips to the micro-level, Kovac tells The Verge, so you have to find some sort of passive mechanism. "Nature is very good at this sort of embodied intelligence," says Kovac. "And as you get smaller, you have to rely more and more on this sort of smart design." This also means there’s less computation involved, which means you don’t have to burden the robots with too many sensors or hardware to control them.

A diagram showing how larger flying animals and robots require more sensors and mechanical parts to perch on things. (Image credit: Science)

The RoboBee platform is far from complete, though. Both the power source used to create the electrostatic charge and the computer smarts that guide the bot are not incorporated into its design — both data and power have to be fed to it via wires. The RoboBee is also very susceptible to disturbances, says Mortiz Graule, one of the paper’s authors, and now a researcher at Harvard. "If someone in the lab runs past it, it affects the flight," he tells The Verge. He says that the engineers had to program the bot to hover, briefly, under surfaces it wants to attach to, as flying at them too quickly would create air currents that might knock it off course. "At this scale," says Graule, "even flying close to a ceiling is very challenging."

The next step is integrating both power source and control systems, meaning they could achieve untethered flight. This could take another two years, in laboratory conditions, and then it would be another five to 10 years before the RoboBee might be ready for use in the real world. Just remember: 20 years from now, if you see a tiny insect stuck onto the side of a building, think twice before you take a swat at it — it might be doing more than just hanging out.

Correction May 20th, 11.37AM ET: The lead author on the study, Moritz Graule, is currently based at MIT, but conducted this research while at Harvard. The story has been corrected to reflect this fact.