Inflatable Dome

The inflatable dome is based on the work of Paul Bourke, formerly at Swinburne University and currently at Western Australian Supercomputing Program WASP. It draws on the innovations made by Paul enabling extremely cost effective planetarium projections to be displayed using readily available components. We'd also like to thank Arts House and the Meat Market for providing us with studio space where we did the initial design, construction and projection testing.

This 3.75 metre diameter inflatable dome is our test dome. It is smaller than the one we will use in productions, however it fits within a large room allowing us to test scenes within. It is a little fragile due to the thin PVC used, and probably wouldn't stand up to too much punishment as it tears on sharp edges quite easily. With some care it will be very serviceable. The weak point at the moment is the entry. The opening is a zippered flap the height of the blue skirt. Consequently you have to crawl in commando style. This is ok for our own testing purposes but would probably want to be remedied with a higher skirt and consequently larger opening. We limited the dome height to the height of the roof in the studio used for construction. This was so we had a reasonable chance of being able to set it up in modest sized rooms for testing.

We will provide more details of the construction of this dome shortly, when we find a space to set it up again and take some more detailed photos. The dome is made up of 12 sections or "gores" which are like long curved triangles. When they are joined they approximate a curved surface. The sections don't finish in a point but are cut off at the top. This is because joining 12 sections at the peak is unweildy to glue and sew. Instead a circular section is sewn in at the top. A skirt (the blue section at the bottom) was added so we could stand up in the dome. We usually don't project on to the lower part, just the grey hemisphere. The dome is made out of thin grey PVC. It is grey because as Paul Bourke points out, a white surface causes greater cross-talk in the projections, light areas reflecting into other parts of the dome projection. The grey minimises this effect. The final dome was sewn onto a tarpaulin, much like a tent. This allows it to be folded up easily, as well as making setup very easy. 1. Unfold the tarp, 2. Peg or weight the tarp. 3. Attach the fan. 4. Inflate. It takes around 20 minutes to inflate with a cheap domestic fan.

Inflated Dome

Dome with Polar Grid test projection

Paper mock-up (not quite right) Notice hole at top to be filled with a circle.

Gore section pattern, opened out. It was folded down the middle, along its length to draw and cut out.

The gore section pattern was cut out from a piece of paper 3 metres long, 1 metre wide. The paper was folded down its length. The curve was laid out from points in the following table along the side away from the fold and then the curve formed by joining the points. The curve was then cut out on the side away from the fold. When the paper was unfolded the full gore pattern was achieved.

From the table below, measure the Distance up the Gore from the bottom of the paper, then mark the width of the gore at a right angle to that height and away from the fold in the paper. You can see that the widths taper in as they go up the length of the gore. They do not form a point as we cut the tip flat which will form a round opening at the top which we fill with a circle of PVC. Once you have marked all the points out, you can join them to form a smooth curve and then cut them out. Then once you unfold the paper you will have the full gore pattern. There is a 5 millimetre seam already in the pattern width, so whan you join the sections along their edge you will have 10 mill overlap. You can add a little to the widths if you want more overlap on the seams. Use the pattern to cut out 12 identical gore sections. A construction guide (see below) will help in gluing the edges of the gores together. I used a pvc glue to initially glue the sections together. The glue didn't stick very well so I also sewed along the seams for added strength.

Gore pattern dimensions. All measurements in millimetres.

Marker	Distance up Gore	Width from centre (fold)
0	5	496
1	152	494
2	300	490
3	447	482
4	594	472
5	741	459
6	889	442
7	1036	424
8	1183	402
9	1330	378
10	1478	352
11	1625	324
12	1772	294
13	1919	261
14	2067	228
15	2214	193
16	2361	157
17	2508	120
18	2656	82
19	2803	44
20	2950	5

Once all the sides are joined, cut out a circle larger that the opening at the top and join the circle to close the opening. Join some lengths of pvc until you have a piece slightly longer than the circumference of the dome. This will be your skirt if you want one. The width of this piece will be the height of the skirt. If you want to enter relatively easily and stand up inside then this skirt should be at least 1 metre width. Attach the skirt to the bottom edge at the circumference of the dome. Don't close off the ends of the skirt, you should have a flap that can be pulled back for entry. Almost done. A length of pvc approximately 1 metre X 2 metres, joined along the long edge will make a small pipe for your fan to blow in. Cut a hole in the skirt slightly smaller that the pipe and attach one end of the pipe away from the door, perhaps 90 degrees around the circumference from the door, and attach your fan to the other end of the pipe. Lastly attach the bottom edge circumference of the skirt to a tarpaulin slightly bigger than the dome. (A 4 metre X 5 metre tarp worked well) Don't sew across the bottom of the skirt where your entry is. Leave at least a large body width at the bottom of the skirt unattached to the tarpaulin, for a flap for entry. If you want you can put a zipper in the ovelapping part between the skirt and tarp to close it off when you have entered.

 

Construction Guides

The curved aluminium arch made it easier to glue the edges of the sections prior to sewing. It is very difficult to glue the sections on a flat surface. The curve of the arch is the same as the curve of the dome. An easy method to work this out is to get some string the length of the radius of the dome. Fix one end to the floor and tie a pen to the other end. On a piece of paper under the pen, trace an arc keeping the string taut. Bend the aluminium strip to fit the arc and fix the strip to a piece of board. The length of the arc doesn't matter too much, around a metre seems ok.

The circle was used to help glue the top piece to the dome sections. This was done last, after the side sections were sewn together.The circle needs to be a little larger than the opening hole at the top. Cut out a circle of PVC also larger than the hole. Place the cardboard under the hole to spread the side sections out against, and glue in the top circular section.

Dome folded up like a tent

Dome packed in sleeping bag cover with domestic fan/heater