If you’re flying on a plane and one of the jet engines suddenly fails, the plane doesn’t just plummet from the sky. The pilot can use the remaining engines, and the plane’s innate gliding ability, to perform a controlled emergency landing. Even helicopter pilots can use a technique called autorotation to slowly descend if the engine fails. But, we still expect quadrotor drones to fail catastrophically if even one of the four props stops turning. Now, thanks to researchers from the Netherlands’ Delft University of Technology, drones can keep flying even when they lose a motor.
Drones are commonly quadrotors that use four motors and rotors to fly, and that isn’t an arbitrary number. Using four motors — two spinning clockwise and two spinning counterclockwise — provides inherently stable flight. That keeps the drone still until it’s ready to change direction, like the tail rotor on a helicopter that counteracts the torque of the main motor. But, that same torque will cause a quadcopter to lose control if one of the four motors fail.
This new technique, however, will keep that drone under control if that happens. If one of the motors fails, a quadcopter will start rapidly spinning because the balanced torque of the motors is disrupted. But, even as the drone starts spinning, the researchers were able to keep it flying. They demonstrate that capability in a wind tunnel, where the drone is able to maintain its position even with high winds. The same technique could be use to give a drone the ability to reach its destination, even after becoming partially disabled.