AI News, Perching Robot Glider Nails Simulated Powerline Landings
- On Monday, February 19, 2018
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Perching Robot Glider Nails Simulated Powerline Landings
The biggest thing holding drones back right now (especially small, inexpensive drones) is arguably battery life.
This is such an issue that CyPhy Works has developed drones that are continuously supplied with power through a tether, and there are other, slightly crazier (or less immediately practical, let's say) ideas about how to provide drones with power on the fly, like lasers or midair wireless power transfer.
But for fixed-wing drones, perching becomes much more complicated, since the drone needs to go from forward flight to something very close to zero velocity in a very small window of space and time.
When talking about aircraft, a stall simply means that the angle of attack of a wing gets high enough, coupled with an airspeed that's low enough, that the air moving over the top of wing separates from the wing itself.
This results in an abrupt decrease in lift and increase in drag, and usually, it's a very bad thing, unless you can pull it off on purpose at exactly the right moment, like just in front of a powerline, as a glider from MIT can do:
Drone on a Wire: UAVs Could Perch on Power Lines to Recharge
Small unmanned aerial vehicles (UAVs) have a big problem: their limited battery power.
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.
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.
Battery Charging of Delivery Drones Copies Pigeons
PhD student Joe Moore, who wrote the paper with former PhD student Rick Cory and Russ Tedrake, an associate professor of electrical engineering and computer science, for the summer issue of Bioinspiration and Biomimetics, says that when his team was first thinking about how to improve UAV agility, they thought it’d be helpful to take cues from birds.
They spent hours researching pigeons and eagles’ abilities to stall — a complex phenomenon that involves flaring their wings, angling their bodies, maintaining high velocity, and accurately judging the trajectory needed to perch.
In this post-stall flight, the bird increases the viscous drag by increasing the surface area of the wing exposed to the flow, but it also exploits the pressure drag caused by the separation of the airflow from the wing;
These results suggest that, at least in the absence of significant disturbances like wind gusts, complex wing morphology and sensing are not strictly required to achieve accurate and robust perching even in the post-stall flow regime.
As described in a 2010 MIT News article, the angles needed to pull it off result in airflow over the wings that is difficult to predict, which is why engineers have designed conventional planes to land the way they do — the long descent, the gradual braking, and the mile-long runway.