3-Star Hubs? What on earth for?

But that doesn’t really answer the question.  Why would anyone need a 3-legged, 3-star hub?

 Suppose you wanted to put a little bling into a Bubble Dome, and add some pentagonal windows?  You need 3-way hubs to do that.  By taking out the yellow struts and the 5-star hub in the middle, then replacing those with ten shorter struts and five 3-star hubs, you get a window that actually looks great and adds strength to the whole structure.   The triangular windows in the Bubble Domes are good for letting in air, but the pentagonal windows let in air with style.  We’re incorporating three of these into the new mini-glamping domes that will be available sometime in July.  We previewed those in a recent R&D blog.

The team was also intrigued by another geometric structure, technically called a dodecahedron.  In laymen’s lingo, it’s a soccer ball configuration, using all 3-way connections.

The model shows that both pentagons and hexagons have to fit together to make it round.  And the sides of the pentagons have to be the same length as the sides of the hexagons – so all the struts need to be the same length.

Would it be possible to build a dome or a sphere with all 3-star hubs?  The engineers said, “No, this won’t work.  The angles for the pentagon need to be 108 degrees, whereas the angles for the hexagon need to be 120 degrees.  You can’t do that.”  The non-engineers, said, “What the heck, let’s try it anyway.  Maybe the flexibility in the PVC will make up the difference.”  The engineers folded their arms and let the kids play.

Of course the engineers were right concerning the math – there’s 12 degrees’ difference in the angles needed.  But similar to how the angles work in geodesics, there’s more than enough flexibility in the PVC pipe to handle the 12 degrees of difference.  We’re calling our partial sphere made with all 3-star hubs and all 10” struts a ‘Dodeca-doghouse’, because its’ 6’ diameter makes it perfect for a full-size dog.  And the dog will probably get smarter the longer he sits in it.

So what can you do with 3-star hubs?  Let’s just say they open up a lot of possibilities for those with very creative minds.  Sonostar sells them, even though there’s not much of a market yet.  After all, it’s not R&D’s job to sell anything, it’s their job to invent stuff.  And 90% of what they do never goes outside the lab.  So for the R&D team, this is actually a success story!