Simple Tensegrity Tower
A simple three-X tensegrity tower made from 3D printed parts
Tensegrity principles (see Wiki link below) combine tension and compression forces to create fascinating structures. The name was first used by Richard Buckminster Fuller. Tensegrity is important in such diverse areas such as skeletal systems, cellular interactions and inter-atomic interactions in molecules. In the very simple design shown here I have used three X's arranged one above the other. You could of course extend the idea to as many X's as you like. Fishing line cords are then used to space, tension and position the X's. If the tension elements (in this case the fishing line) are made very thin the solid pieces of the structure seem to hover in the air. The basic idea can be seen in Snelsons 1948 design in the wiki link below.
The X's and base are 3D printed - the files can be downloaded below. I have also designed a base for the tower (the bottom X simply plugs into the slots). To make the tower simply print out as many X's you want your tower to be made of and then print out the base. Each X has nine holes: two on the end of each arm and one at the center. The two holes at the end of each arm are at right angles to help thread the various lines.
Starting with the first X attached to the base, we pass the fishing line through the holes so that you create a square around the X. Now, instead of simply completing the square at the top, pass the lines through the hole in the middle of the second X, which will go above the first (it will be twisted 90 degrees to the first). Of course these lines will not hold this second X in place (it will just fall down) so we also need to attach lines from the top pair of arms of the first X to the bottom arms of the second X. If we continue in this way, through the structure we will be able to create a simple tensegrity tower. I know these notes are very brief, but I hope you will be able to see how the lines attach from one X to another so that a structure is formed. As you tighten the lines the structure will become rigid (it needs a bit of patience). Once the X's are aligned correctly you can glue the lines going through the central holes of each X piece.
The amount of loading you can place on top of the tower will depend on the strength of the fishing lines and how accuratly you have balanced the forces (tension on the lines) on the whole structure.
I was surprised how rigid the structure becomes ... to see what I mean pick up the tower by the top X and try twisting and rotating it ....
Left: close-up of a base foot that secures one arm of the X. Right: an X-piece just printed-out on the 3D printer.
THE CREATIVE SCIENCE CENTRE
Dr Jonathan Hare University of Sussex, Brighton.
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