Talk:Hoberman sphere

Applications?

Can the hoberman sphere be use for other applications? 03:41, 13 January 2008 by (unknown) [[added section title and original date Jimw338 (talk) 19:02, 8 January 2015 (UTC)]]

Updates?

I work at Liberty Science Center and was told that, as an employee, I shouldn't make changes to content regarding my employer. Having said that, some of the information in this article is out of date. I was hoping someone could change parts of it to make it something like the following:

"Original page declared: The largest existing Hoberman sphere is in the atrium of Liberty Science Center in Jersey City, New Jersey. Fully expanded, it is 18 feet (5.5 m) in diameter. The motorized sphere weighs 700 pounds (320 kg), is constructed of stainless steel and aluminium, and continually oscillates between its compact and expanded states.

The sphere is suspended above the Center's Science Court, and is actuated with a computer-based motion control system. This system opens and closes the sphere in a programmed series of lyrical motions choreographed to music, lighting and special effects. - source: http://www.philipvaughan.net/public.html" Its inventor, Chuck Hoberman, holds several patents on folding techniques, many of which resemble the designs of Buckminster Fuller but for the folding aspect."

If someone could help out, we'd appreciate it!

Auxetic?

Is the Hoberman sphere auxetic? --84.62.204.235 (talk) 07:57, 14 April 2012 (UTC)

Nice question. Assuming it retains its spherical shape when pulled along say the x-axis, it would then expand by an equal amount along the other two axes, which would make it about as auxetic as they come. But I would guess that the spherical shape is only maintained by forcing all six circles to change size with equal forces applied to the circles, which lacks the asymmetry in the definition of "auxetic." If pulling it apart in one direction caused it to shrink in the other two directions then it wouldn't qualify as auxetic. Maybe someone who owns one can do the experiment. If it turns out to be auxetic it might give a novel, perhaps even patentable, nanotechnology for making auxetic materials out of Hoberman nanospheres stuck together. --Vaughan Pratt (talk) 18:34, 17 July 2012 (UTC)

Not a true sphere?

The article says "A Hoberman sphere is not a true sphere, but a polyhedron known as an icosidodecahedron." Actually it's neither or both depending on how you look at it: it's the projection of an icosidodecahedron onto a sphere. The edges of any polyhedron are always straight whereas a Hoberman sphere is made up of six circles. --Vaughan Pratt (talk) 18:17, 17 July 2012 (UTC)

How do you like my replacement sentence? I inserted the word "typically" because I think I've seen small Hoberman models with a cuboctahedral rather than icosahedral pattern. —Tamfang (talk) 18:53, 17 July 2012 (UTC)

Thanks, much better. Presumably the cuboctahedral version uses four circles. With three you'd have an octahedron. I believe those are the only three possible quasiregular polyhedra that one can base a Hoberman sphere on (wish there were more, I could use one with 60 circles). --Vaughan Pratt (talk) 20:13, 17 July 2012 (UTC)

what is the largest diameter effect

what is the largest diameter (as well as volume) increase published at a hoberman sphere I am writing about using them as injected surgical particles to grind away bone or tumors without incisions, that could also possibly function as puff up at body antennas. I thought they had a 10 or 100 times diameter increase.

Angles at nodes

All great circles in the sphere are identical and have ten nodes where they cross other great circles therefore If the circles were disks the angles at the origin would be 36 degrees. Apply the spherical trigonometry law of cosines http://en.wikipedia.org/wiki/Spherical_trigonometry to a cone segment formed by three great circles.

File:Triagular pyrimid with a spherica fromed by 3 great circles

Triagular pyrimid with a spherical base fromed by 3 great circles

 — Preceding unsigned comment added by Kieran Metcalf (talk • contribs) 19:16, 13 January 2014 (UTC) 

$\cos A={\frac {\cos 36\,-\,\cos 36\,\cos 36}{\sin 36\,\sin 36}}.$

$\cos A={\frac {\cos 36\,-\,\cos ^{2}36\,}{\sin ^{2}36\,}}.$

A=63.43494882... — Preceding unsigned comment added by 2.28.138.183 (talk) 15:51, 12 January 2014 (UTC)

Imagine a great circle passing through two nodes with one node in between, this ring would pass through 6 pentagons in this way so the angle at the origin would be 360 degrees / 6 = 60 degrees. Applying the equation for a triangle on a sphere: -

$\cos A={\frac {\cos 60\,-\,\cos 36\,\cos 36}{\sin 36\,\sin 36}}.$

$\cos A={\frac {\cos 60\,-\,\cos ^{2}36\,}{\sin ^{2}36\,}}.$

A = 116.5650512