Wednesday, 22 June 2011

Bell Tower

I played around with models of orthogonal cubes, trying to stack them together. I'd love to build a mega-cube with 20 cubes connecting a larger one, yet I still doubt whether I could easily balance and tune such a large structure.

I would need three columns of tree cubes stacked on top of each other, so I experimented to find out how to stabilise three cubes. Four struts of each cube connect top and bottom vertically, and come very close with simple stacking. I decided to have four central struts, and complete them in the pattern of three stacked cube models.

Bell Tower early draft
The build turned out quite awkward, with some engineering challenges on the path. It took me some hours just to tune the model into a more symmetric shape, and achieved hardly any decent balance. Cubes without diagonal support are inherently instable, so I decided to add cross-bracing tendons to the sides of the structure.

Finally, I was getting more stability and balance, and I began marvelling how to finalise the now sturdy base in a satisfying way. I could easily stack my two cube model over the base, and have an octahedron to top it off.

Bell Tower last draft
Although this experiment created the first 6-level tower I ever made (if you count the base of three levels), balancing was rather unpredictable, and probably hardly stable over time. I had enough leaning towers, and an octahedron on top simply jumped the shark. Finishing the cube-based structure with a 'twisted' cube combined with half an octahedron rather mimics traditional building methods, no need for a wobbly extension on top.

I achieved the final bit of stabilisation by suspending a bell from the four central struts, bringing the centre of gravity down, and dampening lateral movements. I had all aspects together I wanted for that sculpture: a lean base with four central struts, a pointy roof, and a suspended weight. The devil hid in the detail. A cube combined with half of an octahedron can be build with 12 struts, using four joined corners, instead of simply wedging an 8 strut half octahedron on top of a 12 strut cube. Also, the bell had the right kind of weight, but not the looks I wanted.

Bell Tower nearly finished
I spend the first day on building the base structure, the second day with finding a top and suspension, as well as cleaning up the model and fine-tuning. On the third day, it was time to bring everything together. 

Once the bell was in place, the model stood easily balanced, and I installed the last struts without bothering about the wobbly base to work with. The top can now be bend, and the weight of the bell prevents the model from falling over on the rebound. Once in motion, top, base and bell swing in different, connected rhythms, with pressure from the top it rather bends away instead of collapsing.

Bell Tower
Even while blogging, I couldn't stop tinkering. The finishing touches included a cross-bracing of the central struts, similar to the sides, and a tip made with red struts, rotating opposite to the smaller half octahedron underneath. I like the distinct shapes emerging from the red struts from a distance, as well as the sturdiness with all sides cross-braced. 

I used four oak struts (60cm) and 44 bamboo struts with three different length (24 @ 20cm, 16 @ 16cm, 4 @ 28 cm), three types of elastic cord totalling about 12 metres in length, and about 6 metres of nylon cord. Bell Tower measures 90 cm, with a base of 20 x 20 cm, encapsulating a volume of about 35 litres with an estimated weight of about 300 grams. There's roughly at 2:3 ratio in the added length of struts and tendons.

Thursday, 16 June 2011

Leaving symmetry behind

I used a short stint of sunshine to spray paint a batch of struts to bring more colour to my market display. Then I left symmetry behind to experiment with more skewed tensegrities, and came up with five structures in which a splash a colour creates new interesting perspectives.

Disguised Rastafarian
Disguised Rastafarian represents another variation of my favorite octahedron build method, using nylon and elastic jewellery cord together. It's the forth or fifth octa with four green struts hinting at a square, and not the last....

Limejelly revives my old preference for transparent elastic, and for building the 'complementary' tensegrity. Limejelly displays clockwise rotating corners, so their at least two little differences to Disguises Rastafarian.

I think a tensegrity cube allows a symmetric distribution of two colours, yet I continued with a 2:1 ratio in colour distribution, with 4 out of 12 struts coloured green. Balanced on one corner, the green struts appear floating. The box character of the orthogonal tensegrity cube allows for a parallel arrangement for the coloured struts.

Skewed Jellycube
My experiments to transform 12-strut octa and cube into a cuboctahedron inspired Skewed Jellycube. I like the shape and stability of a 12-strut cuboctahedron, but it offers only little play. Skewed Jellycube can be pushed down to collapse in this orientation, although I'm not too sure whether it would survive to vigorous playing.

Skewed Jellyocta
Skewed Jellyocta repeats the idea of Skewed Jellycube, highlighting one of the four potential triangles in a 12-strut cuboctahedron. The structure doesn't collapse entirely, but can be squeezed easily.

With this 80ties retro series the market stall offers enough eye-catching colour, I just need to build some more small icosas and I have a decent collection for the next market day.