Somehow This Robot Sticks to Ceilings by Vibrating a Flexible Disc

It's either some obscure fluid effect or black magic

2 min read
Vibrating disk climbing robot
Image: UCSD

Just when I think I've seen every possible iteration of climbing robot, someone comes up with a new way of getting robots to stick to things. The latest technique comes from the Bioinspired Robotics and Design Lab at UCSD, where they've managed to get a robot to stick to smooth surfaces using a vibrating motor attached to a flexible disk. How the heck does it work?

According to a paper just published in Advanced Intelligent Systems, it's due to “the fluid mediated adhesive force between an oscillatory plate and a surface" rather than black magic. Obviously.

Weird, right? In the paper, the researchers explain that what's going on here: As the 14cm diameter flexible disk vibrates at 200 Hz, it generates a thin layer of low pressure air in between itself and the surface that it's vibrating against. Although the layer of low pressure air is less than 1 mm thick, the disk can resist 5 N of force pulling on it. You can sort of think of this as a suction effect, except that it doesn't require the disk to be constantly sealed against a surface, meaning that the robot can move around without breaking adhesion.

Figure Image: UCSD

The big advantage here is that this is about as simple and cheap as a smooth-surface climbing robot gets, especially at small(ish) scales. There are a couple of downsides too, though. The biggest one could be that 200 Hz is a frequency that's well within human hearing, which probably explains that soundtrack in the video—the robot is, as the researchers put it, “inherently quite noisy." And in contrast to some other controllable adhesion techniques, this system must be turned on at all times or it will immediately plunge to its doom.

The robot you're looking at in the video (with a 14cm disk) seems to be the sweet spot when it comes to size—going smaller means that the motor starts taking up a disproportionate amount of weight, while going larger would likely not scale well either, with the overall system mass increasing faster than the amount of adhesion that you get. The researchers suggest that “it could be advantageous to combine several disk geometries to achieve the desired load capacity and resilience to disturbances," but that's one of a number of things that the researchers need to figure out to properly characterize this novel adhesion technique.

Gas-Lubricated Vibration-Based Adhesion for Robotics, by William P. Weston-Dawkes, Iman Adibnazari, Yi-Wen Hu, Michael Everman, Nick Gravish, and Michael T. Tolley, is available here.

This article appears in the September 2021 print issue as "Curious Physics Lets Robot Crawl Across Ceilings."

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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

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

"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.

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.

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