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Mathematicians have found a hidden 'reset button' for undoing rotation

(www.newscientist.com)
184 points mikhael | 2 comments | 16 Oct 25 15:47 UTC | HN request time: 0.013s | source
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v7n ◴[21 Oct 25 19:12 UTC] No.45660268[source]▶
I was immediately reminded of the anti-twist mechanism, perhaps unrelated but "reset rotation, twice/half" comes up there as well.

https://en.wikipedia.org/wiki/Anti-twister_mechanism

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Syntonicles ◴[21 Oct 25 20:33 UTC] No.45661316[source]▶
What?!

Thank you! I'm working on a robot with a very expensive slip ring, and need to send high fidelity data through it with shielding. I had no idea this was possible this will make things so much easier!

I found a related video you might find interesting.

https://www.youtube.com/watch?v=gZvimEf6DFw

I'm currently studying group theory and SO3 rotations (quaternions & matrix groups) and I'm also curious about the connection. I still have a lot to learn but I wouldn't be surprised if the reset rotation is unique, if we abstract away variation.

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AugusteDupin ◴[22 Oct 25 02:54 UTC] No.45664429[source]▶
As meindnoch points out, the connection needs to loop over the rotating object. That is no problem if the only affect of the rotation that interests you is the centrifugal force.

When you give plasma (not whole blood) the nurses use a centrifuge machine that seems impossible: one tube goes from you to it (carrying whole blood), another tube goes from it back to you (carrying plasma depleted blood). The mechanism of Dale. A. Adams keeps the tubes from twisting. Search “antitwister mechanism patent” for a drawing of the mechanism. As for the principle behind the mechanism, see http://Antitwister.ariwatch.com for a PC program where you can adjust every variable imaginable.

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1. Syntonicles ◴[22 Oct 25 09:38 UTC] No.45666738{3}[source]▶
What a fascinating project. It looks a real labor of love, and I wish I understood it more deeply. I've been making my own visualization sandboxes like this to explore configuration spaces and groups - but for much simpler, more intuitive physical systems.

I went down a few rabbit holes on the site - is this program also written in Basic?

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2. AugusteDupin ◴[22 Oct 25 20:17 UTC] No.45674607[source]▶
Yes, specifically the PowerBasic console compiler version 4 (later versions don’t do animation nearly as well). The PowerBasic compilers are no longer being sold and the company appears to be defunct. Anyway, you can do a lot with a good BASIC compiler.