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# Star Dome

written by Rene K. Mueller, Copyright (c) 2006, last updated Mon, October 8, 2012

 UpdatesFri, May 5, 2006: Extensions such as skylight, door construction and alternative bows, and photos of a model construction. . Tue, April 18, 2006: Added general calculator (simple one), plus canvas calculator, along with more detailed illustrations. . Tue, April 11, 2006: First version, first calculator, and simple construction plan .
 Star Dome Model (with bamboo sticks)
While I was researching the net for bamboo based domes, I came across the Star Dome website. a project of the Kyushu Fieldwork Society, in particular Daisuke Takekawa (Ph.D.) Professor of the University of Kitakyushu, and decided to give a try.

I did a small model, as I usually do when I explore a new form, and I'm very pleased so far, especially since the door can be done easily at the larger triangle at the base, and all bows are the same length, and the position of the junctions is simple to calculate.

## The Structure

According Star Dome , he developed it from a 2V geodesic dome, and finally used 3 bows from each bottom point of the 10 sided polygon.

 Star Dome (virtual model)
 Star Dome, top view (virtual model)

The main advantage over the 2V geodesic dome is apparent:

• 15 (or 30 half) bendable struts (optional add 2 for the base), all the same length
• no connectors, no complicate calculations (e.g. to reduce waste)
• simple bow crossings, which can be tied with cords to provide stability

Star Domes at Night (courtesy StarDome.jp)
2006/04/17 09:54
Star Dome Gathering Space (courtesy StarDome.jp)
2006/04/17 09:55
Star Dome grown green (courtesy StarDome.jp)
2006/04/17 09:54

## The Construction

This is a re-write of the construction procedure, if you want to follow the official procedure please check StarDome.jp: How To (English) .

As mentioned you need 15 full length bows, or 30 half length bows (tied to one long at a time), and drill a few holes to keep the bow crosses stable, or at least mark the crossings in case you plan to tie them:

Step by Step:
 Star Dome Construction: Step 1-4

1. compose a pentagram with 5 bows (blue), and
2. then a surrounding pentagon with 5 bows (green), junctions at the marks
3. prepare the base (red), 10 positions
4. lay the pentagon/pentagram composition over it, and connect the bows accordingly:
• those bows whose ends connect another one, cross them
• loose ends bend so the final bow goes around the center
5.  Star Dome Construction: Step 5
finally use the remaining 5 bows (blue), look at each base connector, and connect there V (two bows go up) is leaning to left, connect right, and where the V leaning right, connect left.

Optionally 5 bows of l/2 length can be used to cross over the top pentagon, and attached to the new formed pentagones around the side (not yet illustrated, but part of the original construction procedure mentioned above), it's suitable in case you plan no skylight.

The "original" star dome is made from split up bamboo, 10cm diameter and then split into 4 struts. Note: It's not sufficient to split it just once as the bamboo is too strong, must be twice splited (1/4th).

## The Formulas

 circumference c = s * 10 diameter d = s * 10 / π bow length lbow = c / 2 floor area afloor = (d / 2)2 * π surface area asurface = (d / 2)2 * 4 π / 2 volume vtotal = (d / 2)3 * 4 /3 π / 2 a = s * cos(π / 5), b = s * sin(π / 5), c = s * cos(π / 10), d = s * sin(π / 10), e = s * cos(π / 3), f = s * sin(π / 3) a-f formulas from Star Dome website

## The Calculator

 Star Dome Sketch, Human Height 170cm
d = m, lbow = m,

Either edit the d or lbow, but not both otherwise d is assumed to be meant.

c = m,
afloor = m2,
asurface = m2,
vtotal = m3

## The Canvas

### Pentagon & Triangles

 The Star Dome Canvas (based on StarDome.jp)
The canvas is pretty straight forward as suggested by Star Dome , in case you care to match the pattern implied by the struts:
• 6x pentagons with side length s
• 10x triangles with side length s

a, b, c, d, e, and f are helping to mark & sew the pattern:
s = cm, a = cm, b = cm, c = cm, d = cm, e = cm, f = cm

Daisuke Takekawa, the innovator of the star dome, recommends to make it 10% larger in case you plan to cover it over the construction.

M. Martin suggested to use "flat felled seam" approach to sew this pattern (or even "overlay" or "interlocked"), it only has to be noted that parts need to be sewn part by part sequentially, and not larger parts (combinations of clusters of pentagons and triangles) together, as it won't fit under the sewing machine - or "one fold", "two fold or "half fold" seam approach is used. Then it's essential to have the opening part (considering the seams as shingle) facing downward to the bottom. I personally would only consider this cover pattern for interior use or sun shade application, but not for serious outdoor (rain cover) application, it's just too complicate and too many parts and seams to sew leak-free.

### Leaf-like Canvas

Of course you also can make a leaf-like cover as well, e.g. choose 5 or 10 leafs, and have one larger triangle at the base be the entry.

The width of canvas lane is wcanvas to compose an entire leaf; in case you want more exact shape numbers, decrease wcanvas and switch to show one segment(s).

nleaves = , wcanvas = m, show segment(s),

 Half Sphere Surface

Which requires apprx. canvas.

 Leaf composition: interior & rain canvas

### Sewing the Cover

In order to sew these leaf-like sphere surface together as rain cover, the water leak is particular to be avoided and so special care of how to sew the seams together:

 Options of Seam Sewing

In case of the star dome a combination of two of the options might be used:

• overlay horizontal canvas stripes or lanes to compose a part of a roof leaf or segment
• use either one-fold or two-fold to patch the leaves / segments together

Consider to seal the stitching holes from sewing with silicon or good clear tape for canvas (with threads) and preferable use water-resistant sewing thread as well.

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