Late last year, we published about a foldable drone from Davide Scaramuzza’s lab at the University of Zurich that could change its shape in mid-air to fit through narrow gaps. That drone included servos to reach a type of different configurations, which made it very flexible but also added a handicap in complexity and weight. At ICRA in Montreal earlier this year, professionals from UC Berkeley showed a new design for a foldable drone, able to shrink itself by 50 percent in less than half a second thanks to spring-loaded arms controlled by the power of the drone’s own propellers.
 
The trick here is that the springs are exerting continuous tension on the passively hinged arms of the quadrotor. It’s enough tension to snap the arms inwards when the motors are off, but when the motors are on, the force that they exert is tougher than the tension exerted by the springs, snapping the arms out again and keeping them there. The actual transition point (where the force exerted by the motors overcomes the tension on the springs, or vice versa) has been properly calibrated to make sure that the quadrotor stays a quadrotor most of the time, and only folds up when you want it to.
 
The researchers got the quadrotor’s trajectory all set up to do the approach, fold, unfold, and recovery, and then aligned the actual window up with that trajectory afterwards. So there’s really no autonomy here, and the quadrotor itself has no idea that the window even exists.
 
It’s viable to look at a folding drone like this and wonder why you don’t just make a mainstream drone small enough to fit through the gaps that you care about, and then call it a day. The reason to make a drone larger rather than smaller is chiefly that it can carry more payload and stay in the air longer, and also because having motors that are farther away from each other makes the drone much more steady and better able to fight disturbances like wind.
 
The great reward of this design is that it adds a reasonably small amount of complexity while still enabling dynamic folding that notably reduces the size of the quadrotor, and in its unfolded state, it’s just as easy to control as a quadrotor that can’t fold. The researchers also say that they could potentially get the quadrotor to fold up into an even more compact configuration—the constraint at the moment is that if it gets any smaller, the blades start to cross, but because each propeller counter-rotates relative to its two neighbors, if you keep them spinning at the same rate “the speed of the blades relative to each other would be small and any collisions between blades would be minor.” That sounds quite tricky, and we’d love to see it in action.



This article is originally posted on Tronserve.com