Easy 30-Push Sphere

one simple element

Easy does it

A couple of years ago I built my first 30-push tensegrity sphere but an important part of this PretensT project is not only that interesting structures get built, but also that the building of them gets easier, faster, and more flexible.

I got to thinking how it might work if I could combine the convenient innovation from more recently, the push bolt, and then also to actually boil it down to one single element for construction.

In this way I’m actually no longer pre-fabricating the whole tension network but instead arriving at a module which contains both compression and tension, and then connecting these together instead.

Just one element

The element needed to build a tensegrity sphere is a kind of “bow” with tension and compression, but with the two exchanged in a way.

Instead of having the compression bend and the tension being drawn back as in the bow above, we have the compression remaining straight and the tension bending (around the sphere shape shortly!)

I can make this kind of element really easily now that I can use push bolts with everything else exactly the same as before.

Each element consists of an aluminum tube, two push bolts, and three segments of cord joined by four rings. We are going to leave all the rings in place, so we actually have double the number of rings now.

The new feature that now comes in to play is that this is now all we need.

Mass production

It’s all fine to have nicely distilled the sphere into one single “bow” element, but that does mean that we need to have quite a number of them, so I set out on my customary mass production process.

There’s no math in this one, because the struts with push bolts are extensible. We just have to have the cord cover approximately one third of the strut length.

By adjusting the nuts we can make the element tight and loose, so it simply has to work in the sphere context if we adjust to the right strut length.

My high-tech cord preparation device has to be set at the right distance to create proper segments.

Quite a number of nuts and rings have to be collected.

In total 30 tubes and 60 bolts of course.

Easy Assembly

Now the fun part begins.

Since we have rings in two places on the cord, we can just insert neighboring push bolts!

It only takes minutes to put together the first pentagon of tension-compression elements.

Turning each of the elements which fan out into part of a new triangle with more struts really begins to show the curvature of the sphere that is starting to appear.

It’s really a quick process to snap these elements together and when you finally get to the last element you can see the complete sphere.

At first it is of course very slack, a lot like maybe a half-flat soccer ball, but if you’ve hung around this site for a while you know that all that’s necessary is turning nuts from this point to make a very tight soccer ball indeed.

Conclusion

By bringing the push bolts into a project that I had done some time ago, and leaving extra rings on the cords, I was able to create elements which allowed for a tensegrity sphere to be assembled literally in a half hour.

When it is tightened, you can see that it even bounces.

Bouncing 30 Strut Tensegrity from Get Pretenst on Vimeo.

But actually the most interesting thing about this sphere is that I was able to completely disassemble it afterwards!