Surprises

My latest strategy to tensegrify objects with a pseudo-corner linking tendons yielded some surprising results. Like mentioned in the last blog, it reduces the total amount of string required, although it might take a bit more time to prepare all components. Building models with those already joined tendons was surprisingly easy, however, precision is paramount, and especially on smaller scale tricky to achieve.

When things come together nicely, magic seems to happen. The shot shows an icosahedron with braided nylon string (not really stretchy), flattened and held together by a paper clip. I was very hesitant to push this model to the limit, yet couldn't stop once it bounced back happily. A collapsible model with non-elastic string, which makes me wonder whether I can build collapsible models of other shapes that do the same. Well, as I have a bit more building material at home I'm not too concerned about having some breakage during the experimental stage.

I want to explore the effect (and potentially integration) of UV light on my structures. The results are already very promising, much better that the photo suggests. Most of the nylon string has already a fluoro colour, spray painting the struts as well could bring some dramatic effects.

Scaling

I used up my supply of recycled struts from my geodesic dome, well, the larger length. Fuller claimed that the ratio of strut to string length remains constant independent of scale - so far, my scaling attempts had quite some errors in it.

As I was curious whether I can use eight centrally joined tendon trinities to build a six strut icosa without any support than my body and dexterity, and furniture nearby. The symmetry of this structure made it so much more elegant (at least conceptually) than most other tensegrity builds. I prepared eight corner joints with three tendons each, based on calculating the string:strut ration from a smaller and larger model.

I even got fancy and used two different colours for the tendons, I hope the different qualities of the string used won't create problems later on. After only one minor hick-up the model came together nicely, with the length I measured being precisely what I wanted according to my calculations. I can imagine that even a bit less tension would provide a stable (not disassembling) model.

The tetrahedron survived some wild storms and still hangs in its slightly hidden space, while three other outdoor installations have gone.

Next big thing

I think I got sufficiently mad during the last week to call myself an artist. I upscaled to a degree that my calculations were quite off the target, and a lot of re-adjustment was required. Three structures with 95 cm struts emerged. The first one, attached to its current destination in a stormy night before the rain hit, still survives the wild weather. The second structure didn't stay for 24 hours in the wild, the latest one still needs some painting and still blocks some of my lounge.

While the tetrahedron exposes some efficiency in the use of materials (roughly a 1:1 ratio of string and tendon), the six-strut icosahedron seems wasteful. The initial string/tendon ratio was about 2.7:1, and as I was running low on nylon strings, I wanted more bang for my bucks. I can't really prove in any fashion that in order to create a tension triangle you can equally to from the corner along its sides or to its center, and the central joints introduced another additional node in the network of strings, but in practise it works just splendidly.

The six-strut icosahedron is a strange tensegrity, connecting the 12 corners of the icosa in a neatly way highly symmetrical through its center. In a way, the minimal 3 strut tensegrity can be understood as minimal octahedron. I better test this experimentally :) Being able to reduce to string/ratio to 1.5:1 made the idea of larger icosas much more viable, and I can't stop experimenting with the result.

I hit a sweet spot with the tendon lengths. Any three struts will balance (all 20 faces), drop and squeezing tests showed a lot of robustness, and the wigglyness can be hypnotising. I won't test it to breaking strength without camera, but I love the options offered by this design in a larger scale. It's simple to suspend small scale objects in the center, some sort of generic 'picture frame' to showcase more complex models.

I wonder whether I can use a set of centrally joined tendons to build from the scratch.