Building a tensegrity structure

 My latest project

 


This turned out to be a bit more fiddly than I expected.  This is partly because I set myself the goal of building it using a single piece of string and it wasn't entirely obvious how to do that without missing or repeating some edges.  Here are my tips:

 

1. Cut 6 pieces of bamboo

Obviously these should all be the same length.  Hollow them out before going any further.

2. Measure out the thread

The thread will pass through each bamboo 4 times, plus there are 24 edges between bamboo ends.  The bamboo sticks are (1+\sqrt 5)/2 times the length of the edges (i.e. the golden ratio!)  You will need a bit more than this to make it easier to tie the ends.  Place two marks on the thread with a pen to identify where the knot should fall.
 

3. Blue tack the bamboo pieces in place

This means creating a ball of blue tack and attaching 3 parallel pairs of bamboo to it in such a way that each pair is at right angles to each other pair.  If you can make the ball of blue tack about 1 unit in diameter that will make it easier later on.
 

4. Pass the thread through the bamboo

It will help enormously if you have a piece of rigid wire that is slightly longer than the bamboo pieces.  Fold over one end of the wire so that it can clamp the thread and pass the whole thing through the bamboo pieces as per the following pattern
 
 
At this point you are one third done.  Now instead joining segment 1 and 9 pass the thread into one of the two as-yet untouched bamboos:
 

Now repeat the pattern to get to two thirds done, and then repeat the pattern again.  Finally tie segment 1 and 25 together aiming to get the two marks you made on the thread to coincide with the knot.

 

5. Tug here and there to get the shape right

If all your measurements are correct there should be no need for this step.  Your tensegrity structure cannot possibly adopt anything other than the correct shape as this would require more thread than you have supplied.  However, in all likelihood there is some slack in the system, and some asymmetries as well.  But with a bit of fiddling around you should be able to make it look respectable.  The closer you are to the ideal thread length the more rigid it will be.
 

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