Drone rotors are no joke and have the potential to cause bodily harm if they are large enough and the rotors have high RPMs. To help prevent cuts and lost fingers, the University of Queensland researchers have designed a quad-rotor safety system that shuts the rotors down when objects get to close to the blades.
UQ’s Safety Rotor platform features plastic hoops the enclose the rotor blades and rotates passively on the same axis. Optical proximity sensors continuously monitor the rotating hoops and once an object comes in contact with the enclosure and a decrease in speed is detected, a safety circuit immediately decreases the speed of all rotors. By the time an object gets near the rotors, the reduced rate of speed is negligible enough to negate damage.
At the base of each hoop are IR reflectors, which continuously ping IR detectors mounted on the rotor hub. If too much time passes between pings, the platform assumes something has interfered with the hoops, and the breaks are engaged. Those breaks are electrodynamic and work by essentially shorting-out the motor inputs, turning them into generators instead. Current generated by those spinning rotors opposes the direction of their rotation- thus the faster the rotation, the stronger the negative torque, the quicker the shut-down.
The researchers measured the latency of their Safety Rotor and found the breaking response from time of object detection to initiating the breaking response was just 0.0118 seconds, and 0.0474 for the rotors to come to a complete stop. The Safety Rotor costs about $15 to $20 in parts and ads about 22 grams to the drone’s overall weight. Not a bad price if you save a few digits.