If you don’t mind a little spinning, quadrotors can operate just fine as trirotors
In 2014, we wrote about some failsafe software from ETH Zurich that allowed a quadrotor to remain fully controllable even with one busted motor. The unbalanced torque generated by three motors means that a quadrotor can’t help but spin, but with a bit of cleverness, software can compensate for the spin and keep the quadrotor stable and even allow it to obey control inputs, allowing it to land more or less safely.
This is a valuable capability, but there are a few things that it doesn’t address. For example, what if your quadrotor loses a rotor over an unsafe area? What if something happens to it when it’s already traveling at a high speed? Or what if it’s trying to deliver something and really needs to make it to its destination, no matter what? At IROS 2018 in Madrid last week, researchers from Delft University of Technology presented a controller that’s able to keep a partially disabled drone flying at a high speed indefinitely, meaning that you have a better chance than ever of getting that taco that you ordered back in 2012.