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Friday, February 28, 2014

First Outdoor Flocks of Drones Demonstrated in the EU

As reported by The Physics arXiv: If you've ever watched huge flocks of starlings wheel and pulsate in the early evening sky, you’ll know how spectacular this phenomenon can be. Starlings probably flock to reduce their chances of attack by predators such as peregrine falcons.

But their are many other reasons why this kind of group behavior is useful—more effectively navigation and foraging, for example. So it’s no surprise that various teams want to reproduce the same kind of behavior in artificial systems.


That’s turned out to be harder than it sounds, particularly for aerial flocking. So while various groups have created semi-autonomous flocks, and one group created a flock of slow-moving blimps in a gymnasium, nobody has successfully demonstrated a fully autonomous flock of robotic flyers that can fly outdoors.

Until now. Today, Gabor Vásárhelyi and pals from Eötvös University in Budapest, Hungary, reveal that they have successfully demonstrated the first autonomous flying robots capable of flockin
g outdoors, just as starlings do.

Flocking is hard because of each member of the flock has to be able to sense its environment and respond to changes quickly and accurately. That means each flyer has to measure its own velocity and position, the position and velocity of those around it, and use this information to calculate what to do next.

Even then, it must be capable of carrying out the necessary flight adjustments quickly. These machines must be able to hover, to fly in a specific direction at a specific speed and to change tack rapidly.

And they must be able to do all this using their own own on-board decision making process.

That’s a big ask but it has looked increasingly possible in recent years given that stable flying machines such as helicopters and quadcopters are now commercially available.

Vásárhelyi start with a commercially available quadcopter known as the MK Basicset L4-ME from the German company MikroKopter. This is capable of self-stabilized flight and is controlled using a handheld remote.

An example of the navigation module used to help provide the
flocking, formation, target tracking, and obstacle avoidance features.
The team’s first step was to modify these machines to make them autonomous. They did this by attaching an extension board carrying a variety of navigational devices such as a gyroscope, accelerometer, GPS receiver and so on as well as a wireless communications unit and a minicomputer.

During flight, each flyer constantly broadcasts its position and velocity to the others which then determine their own actions using the team’s flocking algorithm. This essentially implements two rules, a short range repulsion that prevents adjacent flyers from colliding, and a rule that aligns their velocity and keeps adjacent flyers going in roughly the same direction at the same speed.

Simulation of actual data generated from target tracking exercises.
Two reduce the amount of calculating each flyer has to do, the quadcopters all fly at the same altitude so that the flocking problem becomes a 2 dimensional one.

There is also a ground-based PC monitoring what’s going on and this can make real time changes to the algorithms controlling each flyer. But crucially, the flock does not rely on any centralized control for its behavior.

The results are impressive. These guys have successfully flown flocks with up to ten quadcopters in the air simultaneously. “We successfully established the first decentralized, autonomous multi-copter flock in an outdoor environment, with swarms of up to 10 flying robots, flying stably for up to 20 minutes,” they say.
They also find a number of interesting behaviors. One of the key problems these guys have to handle is the inevitable delay each flyer experiences between receiving information, processing it and then performing the necessary changes in flight.

Target tracking a moving vehicle.
This kind of delay can lead to all kinds of interesting oscillations within the flock. But it can also destroy the flock if it gets out of control. So the flight algorithms must be carefully fine-tuned to damp out the destructive effects.

But with this in hand, Vásárhelyi and co say they were able to fly their copters in various formations such as ring shapes and in lines. They've also observed self-organised behavior in which the quadcopters fly in lines and circles within pre-determined boundaries, just as locusts do in a similar circumstances.

Obstruction avoidance simulation - the flock is attempting to
reach the large geofenced area, while staying out of the smaller
obstacle areas.
There are limits on the behavior of the flocks, of course. The speed of he flyers determines the required braking distance between them to prevent collisions. And in any case, the average distance between the flyers is between 6 and 10 meters. This is determined by the positional accuracy of the GPS sensors which is to within 2 meters or so. Tighter formations will require better positioning accuracy.

Nevertheless, this is an exciting first step in this area. The potential applications for flocks are numerous. The researchers imagine using them for large-scale, redundant observations over wide areas, perhaps for farming, traffic monitoring and, of course, military purposes. And equipped with sensors, flocks could monitor large volumes of the atmosphere for signs of pollution. A real advantage in all this is the redundancy that a flock offers if one unit malfunctions.

With the first success in outdoor autonomous flocks, it shouldn't be long before we see more of these in the real world. Perhaps one day we’ll even be able to watch them gather at dusk and demonstrate their own spectacular aerial displays.

Ref: arxiv.org/abs/1402.3588 : Outdoor Flocking And Formation Flight With Autonomous Aerial Robots