The Safety Rotor—An Electromechanical Rotor Safety System for Drones

We propose a novel rotor safety mechanism for rotary-wing small unmanned aerial vehicles, such as quadrotors, that avoids problems associated with cages, rotor shrouds, and obstacle avoidance safety systems. The system works by using a passively spinning hoop as a mechanical interference sensor; changes in hoop speed are detected with a reflective IR sensor, which triggers an electrodynamic braking circuit. Experiments demonstrated that the system can rapidly detect incipient collisions and bring the rotors of a retrofitted DJI Phantom 3 to a halt from flight speed within 0.06 s of contact. In testing with finger proxies and surface collisions, the safety rotor provided an effective mechanism for reducing the severity of rotor injuries during impact.