Geckos are likely better climbers than any other animal, so it's no surprise that a number of researchers have tried to copy that ability via man-made technology. One group, from Stanford University, was particularly successful with a small climbing robot known as the Stickybot. Four years ago, we heard about how they were also looking into applying the Stickybot tech to a system that would allow humans to climb up vertical surfaces. Now, DARPA has announced the first successful demonstration of that system, known as Z-Man.
In the demo, a 218-lb (99-kg) climber used two hand-held Z-Man paddles – each with a foot stirrup hanging beneath it – to ascend and descend 25 feet (7.6 m) of flat vertical glass. They additionally wore a 50-lb (22.7-kg) pack in one trial.
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Like the Stickybot, the Z-Man system duplicates the structure of the gecko's footpad. On that pad are a myriad of tiny hair-like structures called setae. Each of these are in turn tipped with between 100 and 1,000 even smaller spatulae. Utilizing a type of molecular attraction known as van der Waals force, these spatulae branch out and mesh with the molecules of the climbing surface. Importantly, the spatulae are also able to easily disengage from the surface when pulled in the right direction, without leaving any residue behind.
While it was difficult enough duplicating that structure in the Stickybot's footpads, additional challenges lay in scaling it up to support the weight of a human. It was particularly important to strike a balance between the paddles' adhesive force in both parallel and perpendicular orientations to the climbing surface, to keep the climber from falling off as they detached and then reattached the paddles.
Given DARPA's military mandate, the system is being developed mainly to allow soldiers to scale vertical walls while carrying a full combat load, but without the need for ropes or ladders. The Z-Man project also resulted in the development of a gecko-inspired reversible/reusable adhesive called Geckskin.