Wall climbing

Anyone Can Be Spider-Man With DARPA’s Wall Climbing Invention

Tony Luong

I am suspended near the top of a twenty foot glass plate. All two hundred pounds from me. On land, I can’t do a single pull-up, even if you’re holding a donut over the bar. But I came up here using my own strength, and without my nerves, I wouldn’t have sweated. The suction cups in each of my hands are attached to my waist. The stirrups buckle around my feet. As I shift my weight from my right leg to my left, the pneumatic paddle fingers of my right hand release the pressure that holds the seven suction cups above them against the wall. My body weight shifts to my left leg, pulling down the fingers of the paddle in my left hand. The suction cups on the left paddle push into the wall, forcing microscopic silicone ridges against the glass for maximum surface contact and hold. When I reach the ceiling, I linger, feeling more than a little superhero-like, but also wondering how I’m going to get down.

These loops around my feet are very important. If I lean too far back or to the side – my weight vector is no longer directly under the paddle – this suction will quickly release. I know because that’s exactly what I do. In my excitement to leave the glass wall behind and try out the device on a painted surface, I spread the palettes too far. My foot and weight no longer aligned under the paddles, I slide down the wall and crash to the ground in a tangle of devices and, luckily, rescue ropes.

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Like the feet of a gecko, these suction cups have millions of tiny “hairs” that grip the wall as air is drawn from the suction cups by the pistons below.

Tony Luong

The idea for this piece of equipment – called Z-Man, after the name of the third dimension, or Z-axis – came about a decade ago from DARPA, a group whose mission is to protect the establishment from defense and the nation of technological surprises. Two program directors, John Main and Morley Stone, were discussing the urban battlefield. “We were in the thick of the war in Iraq and a lot of the activity was urban, and the urban heights are the tops of the buildings,” Main says. “We were trying to get people safely to the top of a building.” A study at Stanford suggested that imitation gecko skin could help small robots climb, and Stone and Main wondered if the same kind of technology would work for humans. “Stone shrugged and said, ‘I think so,'” Main said. “And I shrugged and said, ‘I think so. That was the genesis of the whole program.”

“What the gecko does that humans can’t do is flex between two contact points all the time.”

For the past decade, DARPA Z-Man scientists have wrestled with a challenge that has puzzled scientists since Aristotle: how the hell can a gecko climb up and down a tree? And how do we replicate that ability on humans? There were many theories and, in desperate times, the suggestion of magic. But “it’s nothing like magic,” says Main. “If you look at a gecko’s toe, it has millions and millions of tiny ‘hairs.’ it’s climbing or the ceiling it’s hanging from, and they all keep it upright. The phenomenon is based on a physical principle called van der Waals forces, in which atoms in very close contact create a temporary attraction. So they have figured out how the sticking to the wall part happened. Then they had to figure out the actual movement – to translate the mechanics of how the gecko brought its upper and lower feet together to maintain the van der Waals pull, while being able to move freely, even upside down.

Things got frustrating. Whatever the scientists learned, whatever new approaches they took, the results didn’t seem applicable to human use. “This program would have been completed in two years if we could have done exactly what the gecko does,” Main says. “But what the gecko does that humans can’t do is flex between two points of contact all the time. People can’t put their hand on the wall and their foot on the wall, and put a lot of force to make them slide towards each other.” In addition, there are all types of walls. What works on glass may not work on brick, which may not work on metal.

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This frustration was also felt at Draper Labs in Cambridge, Massachusetts. Draper is a non-profit engineering research and development organization that does a lot of highly classified work for DARPA and other branches of government. It’s made up of brilliant scientists, most of whom have no idea what their colleagues in the next room are doing. In one of these rooms, David Carter and Will McFarland made a minor breakthrough. They had envisioned creating paddles for the hands and feet with a silicone “skin” made of nano-ridges, just like those of a gecko. But it still wouldn’t be strong enough to hold most people up against a wall. So they turned their attention to another animal they were studying at the same time: spiders. Watching the insects climb the brick, they discovered an ingenious set of fishhook spines, tightly assembled with the hooks down. These hooks grip the face of the brick without slipping, as long as the spider’s or climber’s body weight is suspended directly below them. Soon they developed hand paddles with tiny metal spines. And those paddles worked, letting you scale any wall, as long as that wall was brick. This led researchers to experiment with steel and iron as well.

The obvious material was magnets, and the pair created paddles that locked and unlocked from the wall by moving a handle on the paddle up or down. Attach your legs and you can climb any surface, as long as it’s metal. The uses were immediately apparent. “There are a lot of steel structures like oil rigs that people needed safety and climbing gear for,” Main says. The magnetic paddles, which are pictured on the cover of this issue, were licensed to high-end military supply company, Atlas Devices, and rumor has it that the technology is already being used by special operations forces to ride on ships, tankers and oil rigs.

On land, I can’t do a single pull-up, even if you’re holding a donut over the bar.

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Tony Luong

So now scientists had a way to scale brick and a way to scale metal. But they had nothing for smooth, non-magnetic walls. By this point, Main had cycled out of DARPA, worked for a startup for seven years, and returned. When he returned, the mood was worse than when he left. Much worse. “There is a mandatory step in every technology project,” says Main. “This is the desperation stage. This happened when we had been working on Z-Man for a while but were in a rut. The idea of ​​using suction came about because of the frustration of being in this rut.” Desperation, in this case, was a good thing. “That’s when creativity and drive kick in, and something great happens.”

The problem with the nano-ridged silicone skin that Carter and McFarland had previously described was that the surface couldn’t get close enough to the walls to activate van der Waals forces. They had also tried simple suction cups, but these could only hold the climbers in place. There was no way to release them and reaffix them to actually climb. Under Carter’s leadership, Draper’s team was inspired to combine gecko skin and suction cups with leg power. Their new paddle was made of synthetic gecko skin layered inside suction cups. To increase the effectiveness of these suction cups, they attached foot stirrups to a series of pistons. When the foot stirrups are depressed, the pistons evacuate the extra air inside the suction cups. This smashes the nano-ridges against the surface of the wall, activating van der Waals forces. And when the suction is released by lifting the climber’s weight from the stirrup, the paddle can be easily moved elsewhere. The cost is equally impressive: Carter and his team estimate that each pair will only cost $3,000 to $5,000.

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Tony Luong

Although it takes three types of paddles to conquer any surface instead of just one, Main is confident that the technology will one day be combined into one device. Like all military contractors, DARPA is suspicious if, where, and how the Z-Man was deployed in the field. “Use your imagination” is all Main will say. Which is probably the same advice he gave when he challenged Z-Man ten years ago.


*This article originally appeared in the December 2016/January 2017 issue of Popular mechanics.

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