There are millions of Brazilian Free-tailed bats living in caves across Texas, and every night, those bats are somehow able to swarm through the air without crashing into one another. The researchers at Boston University's Intelligent Mechatronics Lab wanted to know what the bats' secret was, so that it could be applied to the flight control algorithms for their autonomous unmanned aerial vehicles (UAVs). In order to learn more, they decided to fly a remote-control UAV into one of these bat swarms, and record the creatures' reactions with three ground-based high-speed FLIR cameras, and on on-board 3D HD camera. The craft that they used, named the Batcopter, is a classic example of seat-of-the-pants engineering.

The original


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Since it would be used in rural Texas, where high-tech suppliers aren't close at hand, it was decided that the quadcopter aircraft should be made mostly from parts available at ordinary stores - in case anything broke, and needed to be replaced. Therefore, the original Batcopter was made with an aluminum frame, the arms of which were actually chromed aluminum towel racks from Home Depot. The copter was encased in netting, to protect itself and the bats from one another. That netting was attached to a box made from fiberglass kite rods, which was in turn attached to the Batcopter with bamboo rods.

The combined weight of the UAV frame, netting frame and 3D GoPro camera was approximately 1.3 kilograms (2.9 lbs). Although the four motors were able to handle that load in Boston, the higher temperatures and altitude of Texas proved too much. The Batcopter couldn't react quickly enough, and needed to be made lighter.

Batcopter 2.0

Among the spare parts brought along from the lab were some carbon fiber rods, and pieces of blue packing foam. The rods replaced the aluminum frame, while the foam and some wire replaced the fiberglass rods used to hold the netting. A salesman at a local hardware store suggested using white glue-impregnated twine to hold the carbon fiber rods together, which is what the team did.

A hunting supply store donated some carbon fiber arrow shafts, that ended up being used to add some much-needed rigidity to the new frame. The motors/rotors, control unit and battery were mounted using zip ties, double-sided tape and bamboo. Altogether, the second version of the Batcopter was an estimated 500 grams (17.6 ounces) lighter than its predecessor.

In the air

The UAV's first flight amongst the bats went well, although it did crash once when one of the rotors got caught in the netting. This caused one of the carbon fiber rods to buckle, but the aircraft was deemed to still be airworthy. Although it was indeed still able to fly the next day, one of its rotors snagged a strand of the buckled rod, causing a crash that permanently grounded the Batcopter.

As can be seen in the video below, however, the Intelligent Mechatronics Lab team did get some prime "flying with the bats" footage, which will hopefully provide some inspiration for next-generation UAV flight control systems.

Source: IEEE Spectrum

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