four-fold garden-stake-and-nylon-twine tensegrity obelisk standing outdoors

On October 21, 2003, I finished assembling this tensegrity obelisk. I have attempted obelisks before (see First Obelisk and Second Obelisk). This new obelisk is mostly a variation on the first obelisk I assembled. Like that one, it is composed of 4-foot (1.22 m) hardwood garden stakes (all recycled from disassembled structures, including the first obelisk) knitted together with nylon twine. It is 9 feet 1-3/4 inches (2.788 m) tall which is approximately the height of the first obelisk.

The main innovation of this structure is its four-fold geometry vs. the three-fold geometry of the first obelisk. The main benefit of the four-fold geometry is to give the structure a firmer base. Triangular bases seem much more unstable to me. In addition, I doubled all the tendons. This wasn't necessary for strength, but to make the tendons less elastic. This will help if I ever grow vines on the structure I think. For a taller, unloaded structure, I would double the tendons on the layers closer to the base and leave the ones higher up single.

See the datasheet for a schematic and annotated computer-rendered views of the obelisk. Some of the tendons near the base are a little looser than I'd like. I'd tighten them up if I did the design again. This model is available in the Tensegrity Viewer as "4-Fold Obelisk".

axial view of four-fold garden-stake-and-nylon-twine tensegrity obelisk lying on its side outdoors
Axial View of the Obelisk

Seven-fold Equi-tendoned Prism Index Skew Four-Prism