Drones that carry things come at many different scales. On the smaller end, you have delivery drones, real or imaginary. On the larger end, you have…well, delivery drones, I guess, but ones that are full-size helicopters, that can deliver entire crates of supplies autonomously. Once you start thinking about how to deliver objects much bigger than a breadbox, it stops making sense to try and stuff all of your stuff inside the drone itself, and you end up having to hang it from the outside. Hanging things from fast-moving aircraft with cables results in payloads that swing around, and controlling that swing can lead to more stable payloads, and other, way more exciting things.
A significant amount of work has been done getting drones to manage cable-suspended payloads with as little swing as possible, since it seems like having the load at the end of a cable swing around a bunch would be a bad thing. And it is a bad thing, unless you’re swinging it around on purpose to achieve an objective. Here’s one spectacular example of what can be done with a cable-suspended payload if you’ve got the skills:
Here’s another video of similar maneuvers from the perspective of the pilot.
But why would we need quadrotors to be able to do things like this? Researchers in Vijay Kumar’s lab at the University of Pennsylvania have some examples:
To demonstrate that such a capability would be necessary, two motivating scenarios are brieﬂy presented next. For instance, to enable a UAV carrying a long cable suspended load to enter / exit short openings (such as a window), the load needs to be dynamically swung into the opening, such that the tension in the cable goes to zero at the right point in time. This enables the UAV to go through the window while the load undergoes free fall, prior to the tension in the cable being reestablished. Alternatively, to enable UAVs to transport suspended loads while ﬂying under a strict ceiling height, either to avoid radar detection or when ﬂying indoors, requires dynamic motion of the load to avoid large obstacles on the ground.
And here’s what these maneuvers might look like:
Have you ever wondered how Google plans to deliver packages to you by drone if you live in an apartment building? Obviously, they’re going to get their delivery drone with its dangly cable contraption to swing packages right through your windows!* Let’s just hope the window is open.
[ Vijay Kumar Lab ]
* Of course we are joking. Through-window package delivery seems like a terrible, terrible idea.
Evan Ackerman is a senior editor at IEEE Spectrum. Since 2007, he has written over 6,000 articles on robotics and technology. He has a degree in Martian geology and is excellent at playing bagpipes.