Thursday, 14 April 2011

Frog in the well

Frog in the well
I went to the local hardware store to find a small table saw. It could make preparing wooden struts much faster and even more precise than the Dremel, but I'll have to wait to find out. Instead, I brought a 3m aluminium tube home and got busy.

The first hole I drilled was too wide to hold a knotted nylon string, yet I decided to worry about this fact later and prepared three alu struts for a prism, each with three equidistant holes about 2cm from the end. Doubling the tendon should provide additional strength, and a knot of two strings of nylon held safely in the hole.

I used the measures taking from a bamboo strut structure with nearly 1m struts. I adjusted the final tension by pulling the vertical tendons overly tight, and then knotting off between 2 and 5 cm of it. I ended up with the box shape I wanted, with decent tautness. I did a stress test by putting a zabuton on top, and it took the load nicely.

I pushed the end of the strings back, and riveted the end of the tubes. The construction details hidden, not perfectly but nicely balanced, evenly spaced holes made it a satisfying piece by itself. Yet it invited me to do more, to use it as base for a more complex tensegrity.

After installing two bamboo tensuls into the top triangle, and playing around with spheres on top of them, I build a 30-strut icosahedron with nylon strings. I chose a strut length I didn't use before, and estimated the string length required, with nasty consequences. The overall tension split one after another strut, as could drops from just one meter height.

The drop resistance might not have improved, yet in its current installation the structure is unlikely to be exposed to excess stresses. The sphere now rests on a single smaller tensul, with a 3:1 ratio of strut length from basis to middle part, and a 3:1 ratio of strut length and upper triangle of the support for the sphere.

Instead of a tension triangle, the base of the support prism get its tension from three connected nylon string loops, connected to the lower end of the struts. A small Chinese bell with a frog sitting on it is suspended from the center.

Now all I need are three columns to elevate the model some more. The aluminium struts were easier to work with than I thought, and invite bigger structures.

No comments:

Post a Comment