Spring-Loaded Drone Collapses Mid-Flight to Zip Through Windows

This drone can dynamically fold and unfold its arms to pass through narrow gaps

2 min read
Design and Control of a Passively Morphing Quadcopter
The UC Berkeley morphing drone in the unfolded (top) and folded (bottom) configurations. The drone changes shape without the use of any additional actuators: When low thrust forces are produced by the propellers, springs pull the arms downward into the folded mode. When high thrust forces are produced, the vehicle transitions into the unfolded mode.
Image: High Performance Robotics Lab/UC Berkeley

Late last year, we wrote about a foldable drone from Davide Scaramuzza’s lab at the University of Zurich that could change its shape in mid-air to squeeze through narrow gaps. That drone used servos to achieve a variety of different configurations, which made it very flexible but also imposed a penalty in complexity and weight. At ICRA in Montreal earlier this year, researchers from UC Berkeley demonstrated 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 constant 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 stronger 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 carefully calibrated to make sure that the quadrotor stays a quadrotor most of the time, and only folds up when you want it to. 

There is, however, just a little bit of fudging going on in the above video—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 possible to look at a folding drone like this and wonder why you don’t just make a conventional 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 primarily 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 stable and better able to resist disturbances like wind.

The big advantage of this design is that it adds a relatively small amount of complexity while still enabling dynamic folding that significantly 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 intersect, 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. 

“Design and Control of a Passively Morphing Quadcopter,” by Nathan Bucki and Mark W. Mueller from UC Berkeley, was presented at ICRA 2019 in Montreal, Canada.

[ HiPeRLab ]

The Conversation (0)

How the U.S. Army Is Turning Robots Into Team Players

Engineers battle the limits of deep learning for battlefield bots

11 min read
Robot with threads near a fallen branch

RoMan, the Army Research Laboratory's robotic manipulator, considers the best way to grasp and move a tree branch at the Adelphi Laboratory Center, in Maryland.

Evan Ackerman

“I should probably not be standing this close," I think to myself, as the robot slowly approaches a large tree branch on the floor in front of me. It's not the size of the branch that makes me nervous—it's that the robot is operating autonomously, and that while I know what it's supposed to do, I'm not entirely sure what it will do. If everything works the way the roboticists at the U.S. Army Research Laboratory (ARL) in Adelphi, Md., expect, the robot will identify the branch, grasp it, and drag it out of the way. These folks know what they're doing, but I've spent enough time around robots that I take a small step backwards anyway.

This article is part of our special report on AI, “The Great AI Reckoning.”

The robot, named RoMan, for Robotic Manipulator, is about the size of a large lawn mower, with a tracked base that helps it handle most kinds of terrain. At the front, it has a squat torso equipped with cameras and depth sensors, as well as a pair of arms that were harvested from a prototype disaster-response robot originally developed at NASA's Jet Propulsion Laboratory for a DARPA robotics competition. RoMan's job today is roadway clearing, a multistep task that ARL wants the robot to complete as autonomously as possible. Instead of instructing the robot to grasp specific objects in specific ways and move them to specific places, the operators tell RoMan to "go clear a path." It's then up to the robot to make all the decisions necessary to achieve that objective.

Keep Reading ↓ Show less