In contrast with commercial aircraft that can easily continue to fly even if one of the engines stops working, for quadcopters (drones with four propellers) the failure of one motor is a bigger problem. With only three rotors working, the drone loses stability and inevitably crashes unless an emergency control strategy sets in.
Researchers at the University of Zurich and the Delft University of Technology have now found a solution to this problem. They show that information from onboard cameras can be used to stabilize the drone and keep it flying autonomously after one rotor suddenly gives out.
"When one rotor fails, the drone begins to spin on itself like a ballerina," explains Davide Scaramuzza, head of the Robotics and Perception Group at UZH and of the Rescue Robotics grand challenge at NCCR Robotics, which funded the research. "This high-speed rotational motion causes standard controllers to fail unless the drone has access to very accurate position measurements." In other words, once it starts spinning, the drone is no longer able to estimate its position in space and eventually crashes.
One way to solve this problem is to provide the drone with a reference position through GPS. But there are many places where GPS signals are unavailable. In their study, the researchers solved this issue for the first time without relying on GPS, instead using visual information from different types of onboard cameras.