If there's one thing that's scary about quadcopter drones – besides their ability to invade peoples' privacy or fall on their heads – it's those fast-spinning and potentially skin-slicing rotor blades. An experimental new system, however, is designed to stop the rotors before they can do any cutting.

Known as Safety Rotor, the system was developed by a team from Australia's University of Queensland, led by Dr. Paul Pounds.

It incorporates four lightweight plastic hoops, each one of which is mounted on one of the drone's sets of rotors, extending out to surround the rotor blades. The spinning of the rotors causes the hoops to spin with them, but because the hoops are mounted via a low-friction bearing on the rotor shaft, they don't spin as fast (or thus as dangerously) as the rotors, and can be stopped independently of them.

Should an appendage such as a finger accidentally wander towards one of the rotors, it will get hit by the hoop before making contact with the rotor blade itself. This causes the hoop to stop rotating, which is instantly detected by an infrared optical sensor mounted below the hoop, on the drone's rotor arm.

That sensor subsequently prompts the microcontroller driving the rotor's motor to apply an electrodynamic braking system. This will stop the blades from spinning, in less than 0.06 of a second from the time that the finger touches the hoop.

In its present form, a complete Safety Rotor setup weighs about 20 grams. It could reportedly be retrofitted to an existing drone for around AUD$15 (US$11), only minimally obstructing air flow or reducing flight time. That said, if the system were mass-produced and built into drones, it could conceivably cost manufacturers less than $5 per unit.

Pounds' team recently presented Safety Rotor at the 2018 International Conference on Robotics and Automation, and is now looking for partners interested in commercializing the system. It's demonstrated in the video below.

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