# Do the Twist

## constructing in push-pull space

## Our building block

Last time we saw the simple foundations of *elastic interval geometry* and ended with the elegant pure scenario of having *push* separated from *pull*, as two completely different kinds of *intervals*. This is the way we will continue, because this distinction and the constraints it adds are very revealing and beautiful.

Given the push/pull separation, we **can only build** with *twists*, and we start with the simple one with with three bars, held by a network of cables.

Whether virtual or physical, this is the form they have when they are in the middle of the model:

## Collapse the tension hexagon

To connect two twists together, we use a ring of tension. The bars of both twists must press outwards, and this hexagon of tension between them brings them into a force relationship together.

The hexagon of tension can also be turned into radial tension lines when the neighboring twists are not available to push outwards to hold the hexagon in place.

The hexagon is regular, so the triangles are the same, and all of the lengths can stay exactly the same. We can also take away the doubling of the lines so the radial tension has singular cords.

Think of this radial tension pattern as a *connectable face* of the *twist*.

A lone *twist* uses this radial tension instead, and it also must be used when a twist is in the end position.

Here is a *left twist*:

Here is a *right twist*:

Eventually, using your hands, you can learn to easily distinguish a left twist from a right twist.

These *twists* have two *connectable faces* each.

## Two radials become a hexagon

Bringing two lone *twists* together so that their end points form a hexagon, we can basically **reconnect** the two sets of three cords into one new hexagon.

Six cord segments, simplly rearranged:

Each of the two original twists has **two connectable faces**, top and bottom. Here we have connected the top of the *right twist* to the bottom of the *left twist*, now in a force relationship with each other through the tension hexagon.

When they are connected, there are only two connectable faces remaining: top and bottom.

## The Omni-twist

Adding the two *twists* together this way gives us six bars, but there’s **another way** to connect up six bars, and that it using radial tension everywhere.

Here you see it with and without tension:

Notice that the color of the bars is different. That’s because they actually need to be a bit **longer** than the others from the original twists above, to keep the radial tension lines are **exactly the same**.

This structure is called the *omni-twist* because it has **eight connectable faces** as compared to the *twist’s* two!

The faces of the original *twist* and the *omni-twist* fit together perfectly! We have the blocks we need to build some interesting things.

## Coming up next

This has been a quick introduction to the building blocks and the way things connect up.

Next we will take a step back and look at how the math underneath works. It’s all just arrows.

## Pretenst Constructions:

**2021-04-08: "Bow Tie Tensegrity": better bend resistance**

**2021-03-29: "Six Twist Essential": what if more hands could see?!**

**2021-01-25: "Minimal Tensegrity": no more tension lines than absolutely necessary**

**2021-01-18: "Degrees of Freedom": first adjustable hybrid tensegrity**

**2021-01-11: "Fractal Experiment": a tensegrity of tensegrities**

**2020-12-09: "Axial Tension": pretensing what is already pretenst**

**2020-11-02: "Halo by Crane - Part 2": the strengthening**

**2020-10-26: "Halo by Crane - Part 1": assembly complete but strength lacking**

**2020-10-12: "Brass and Tulips": a tight and strong tensegrity tower**

**2020-08-10: "Prefab Tension Tower": the tower of eight twists**

**2020-07-27: "Elastic Bubble": building with elastic ease**

**2020-07-13: "The Twist Sisters": left-handed and right-handed**

**2020-07-06: "Radial Tension": Pulling towards the middle**

**2020-06-22: "Diamond of Tension": Four pulls for every push**

**2020-06-15: "Prefab Tension": Separating compression from tension**

## Software:

**2021-03-10: "Do the Twist": constructing in push-pull space**

**2021-03-01: "Elastic Interval Geometry": pure pairwise push and pull**