Drone on a Wire

from popularmechanics.com

Small unmanned aerial vehicles (UAVs) have a big problem: their limited battery power. But researchers at MIT’s Computer Science and Artificial Intelligence Laboratory are developing a way to extend the range by having drones act like birds. If a drone can land on a power line, the thinking goes, then it can exploit the electricity running through power lines to recharge.

The key is getting the UAV to land right on a skinny line, which, given the slim margin of error involved, is no easy task. But both indoor and outdoor tests have gone well, and this week the MIT lab released a video showing a foam glider homing in on a power line and snagging itself on a string drawn in front of it.

“Our work demonstrates that we can execute accurate, high-speed flight maneuvers with a fixed-wing UAV using low-cost onboard sensors,” says Joseph Moore, one of the research assistants on the project.

A drone, Moore says, cannot rely on its camera to guide it to a power line. The typical urban setting is simply too cluttered to estimate the range to a target (assuming it can be seen at all). In addition, the frame rate of most cameras is too slow for a landing that must be executed in less than a second.

So the MIT glider employs instead a magnetoresistive magnetometer. This sensor helps the UAV zero in on an electrical power line by locating the magnetic field it produces. It is very precise—and it has to be. “You need to be within 6 cm of the power line,” Moore says. “If you miss that, you fall off the power line.”

In these tests, the small drone was only 3.5 meters (11.5 feet) from the power lines when launched. However, the magnetometer has a range of only four meters total, so a real UAV operating in the field would need to depend on GPS points gleaned from satellite imagery reach the general vicinity of a power line.

Moore won’t go into great detail about the recharging process because the MIT team has yet to patent its solution. He does, however, outline three basic options. First, there is inductive coupling, whereby the drone’s claws form a transformer around the electrical line. Alternately, a UAV could pierce the line and draw current directly from it. Finally, the drone could harvest energy from the electrical coronas formed by very-high-voltage lines.

The MIT project, which is funded by the Office of Naval Research, Air Force Research Laboratory, and DARPA, is set to wrap up this summer. In the meantime, there are a few outstanding issues to address. For example, the lab will need to partner with mechanical design experts to develop a complex grasping mechanism. For the tests, a simple hook was used.

The team is also looking at biomimetic features, such as hair-like sensors running along the wings of the UAV to measure airflow. “If we can measure the wind, we can use the wind to improve the mission duration of our vehicle,” he says. “We experimented a little with flapping robots,” Moore notes, but adds that researchers decided to keep things simple. More complicated designs, he says, “are on the horizon.”

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