Birds and bees make perching look easy, but creating a tiny aerial drone that can land on—and then re-launch from—a wall, tree branch or other surface takes a lot of work. Such micro aerial vehicles (MAVs) have previously used spikes or magnetic landing gear, and expend a lot of precious power to take flight again. But researchers from Harvard University, Massachusetts Institute of Technology and several other institutions have created a minuscule wing-flapping robot that literally turns the problem on its head—with a disklike top that can cling to most surfaces using static electricity, much like rubbing a balloon and sticking it onto a wall.
The “electroadhesive” MAV can hang from the bottom of a wood or glass surface, or even a tree leaf, by creating electrostatic attraction between the surface and the electrode in its head. The power needed to maintain the electrostatic connection is “three orders of magnitude” less than that required to keep the MAV in flight for the same amount of time, the researchers wrote in a report published Thursday in Science. “Running out of power becomes a bigger problem the smaller the vehicle is,” says Moritz Alexander Graule, one of the report’s co-authors and a PhD student in MIT’s Department of Mechanical Engineering.
The ability to hang from a structure rather than rest on top also provides the MAV with a less-obstructed view of the area below and protection from extreme weather conditions during long perching sessions. The headfirst electrostatic approach works by changing the charge distribution of the material to which it is clinging, Graule says. This works best with a smooth texture, so the drone can adhere better to something like a window than to a rough or porous surface. The MAV’s electroadhesive connection is not particularly strong, however, which means the drones need to weigh in at roughly 84 milligrams—less than a bee. In order to relaunch the drone cuts power to the circular copper electrodes in its disk and restarts its wings.
Other aerial mini drones under development use more mechanical approaches to perching. Stanford University’s scansorial UAV uses onboard sensors to detect a wall, for example, and then performs an inflight maneuver to land and cling using microspines on its legs, according to Mirko Kovac, an engineering professor at Imperial College London’s Department of Aeronautics. Kovac’s article in this week’s Science analyzes the latest developments in MAV flight. In terms of energy conservation other ideas under consideration include leveraging wind gusts to alleviate flight strain on batteries or even developing ways for smaller MAVs to perch on larger ones midflight so they can travel greater distances without using additional energy, Kovac says.
The big remaining challenges for the researchers involve integrating a battery and microprocessor that can make their MAV more autonomous. The current mini drone relies on a wire tether to deliver power and data from external sensors to determine its position while flying but the researchers want to build a battery-powered version with enough onboard power and intelligence to fly untethered. They have also considered the possibility of enabling the drone to stick to vertical surfaces as well. The ability to cling to a wall requires not only more adhesive power but also a way for the MAV to orient itself so that its wings do not interfere with the landing.
Such a drone might be one or two years away in the lab, and as long as a decade away from being ready for more widespread development and use, says Robert Wood, the project’s principal investor and a professor at Harvard’s Paulson School of Engineering and Applied Sciences. “I see applications in search and rescue, hazardous environment exploration—basically any situation where you want to have low cost and distributed sensing [that] would be too difficult or too dangerous for a human,” Wood says. He believes more immediate benefits from this research will come from solving the technological challenges of developing devices at this scale from scratch. Wood and his colleagues now use the microfabrication techniques developed to build their MAV to likewise create articulated and sensor-laden microsurgical tools geared toward minimally invasive surgical procedures.