from Hacker News

New suction-cup system spins water to stick to rough surfaces

by anon463637 on 1/18/20, 7:55 AM with 33 comments

by czr on 1/20/20, 5:00 AM
actual paper https://aip.scitation.org/doi/10.1063/1.5129958
video 1 (response measurement): https://aip.scitation.org/doi/suppl/10.1063/1.5129958/suppl_...
video 2 (picking up block): https://aip.scitation.org/doi/suppl/10.1063/1.5129958/suppl_...
video 3 (hexapod): https://aip.scitation.org/doi/suppl/10.1063/1.5129958/suppl_...
video 4 (human climbing tiled wall): https://aip.scitation.org/doi/suppl/10.1063/1.5129958/suppl_...
video 5 (human climbing concrete wall): https://aip.scitation.org/doi/suppl/10.1063/1.5129958/suppl_...
by NougatRillettes on 1/20/20, 12:42 PM
My understanding of it after a quick read of the paper: you want to make a suction cup. The usual way is with a solid cup (think plastic) with a softer rubber-like ring around it. Near the ring, you will have atmospheric pressure (high) outside, and vacuum pressure (low) inside, so if the ring doesn't make perfect contact with the surface, some air is going to come in and ruin you vacuum. What they are doing is that they are rotating a bit of water in the suction cup, which because of centrifugal force will come close to the suction cup frontier in a ring-like shape. This water ring will -- thanks to fluid mechanics black magic -- have a different pressure at its exterior and its interior. Its interior pressure will necessarily be the same as the vacuum, and you can make it so that the pressure outside is the same as the atmospheric pressure, hence, according to this paper, if the rubber ring fails to make hermetic contact, air won't come in because at the frontier of the cup, the pressure is the same both outside (atmosphere) and inside (exterior of the water ring).
by ta1234567890 on 1/20/20, 4:46 AM
Pretty cool. Reminded me of what this guy is doing, he calls it "orthosonic lift": https://youtu.be/kG6vXGidQbo
Some more info: http://sciencechatforum.com/viewtopic.php?nomobile=1&f=77&t=...
I believe he has a couple of patents on the technology, but not sure he'll ever get around to making something practical with it.
by raihansaputra on 1/20/20, 7:09 AM
Quick links to diagrams explaining how it works:
https://aip.scitation.org/na101/home/literatum/publisher/aip...
https://aip.scitation.org/na101/home/literatum/publisher/aip...
(from the actual paper link from czr: https://aip.scitation.org/doi/10.1063/1.5129958)
by flashman on 1/20/20, 5:16 AM
Kind of similar to the reason you'd wet a suction cup before using it: the water helps plug any small air gaps. But in this version, a fan spins the water and air inside the cup, with the heavier water being forced to the edge, and any water leakage being replaced from a reservoir.
by catalogia on 1/20/20, 4:31 AM
Is this the same mechanism as the immersion blender trick? (https://youtu.be/TrZyuCh9df0?t=424)
by AliAdams on 1/20/20, 8:35 AM
What about ferromagnetic fluid? You can still spin it if you are aiming to push it 'centrifugally' into the features of the vacuum boundary, but you shouldn't lose a lot during the detachment.
(Plus it looks much more sci-fi.)
by jcims on 1/20/20, 4:30 AM
No idea if this is actually a new idea but it's definitely new to me and I love seeing it. What a cool concept, likely to be a few applications in industry beyond spiderbots.
by Terr_ on 1/20/20, 7:33 PM
> The resulting inertial force generates a steep pressure gradient, allowing a high vacuum to be maintained at the center of the cup's vacuum zone
Sounds like a "momentum transfer" vacuum pump, shaped so that the output side bleeds out along the rim.
https://en.wikipedia.org/wiki/Vacuum_pump#Momentum_transfer_...
by jakedata on 1/20/20, 2:12 PM
I can't say I am super looking forward to hexapod wall climbing robots.