mxa's blog

Greg from the Small Planetarium group asked me about the patterns I used for the cover. Well, they're really very simple! Click on the images on the right to see the sketches I made while laying out the cover. I use the same color coding as used in the 4v assembly diagram at DesertDomes. As mentioned before, the cover is composed of three layers of five segments each, connected end-to-end in a ring.

The bottom layer has the largest segments (16 triangles each). I wanted to use the sewing technique described here, which meant adding a little extra fabric (borders) around the perimeter of the segments. On the bottom layer segments, I had to add wide borders to the left and top, and narrow borders to the bottom and right. The little wedges within the segments are not cut out, but folded up and sewn flat against the cover. If you're planning on using your dome outside, make sure that the opening of the fold is always pointing downwards, to prevent rain pooling in the seam. The result is a piece that cannot be properly folded, since it is already beginning to be curved.

If you want to be able to enter and exit your dome without having to lift the entire thing (highly recommended!), you'll need to design in some kind of a doorway. I did this by making a vertical cut in one of the bottom segments, straight down the middle of the purple/green/green and purple/purple/purple triangles. I put in a zipper and also added a little awning, which you can see in the photo of the finished dome.

The segments of the middle layer are 12 triangles each. The top of each segment has a wide border, the other edges (left, bottom and right) have narrow borders. Note that I moved the wedge on the left inward (by rotating the red/yellow/yellow triangle against the other red/yellow/yellow triangle. The reason for this is that otherwise, there would be too many layers of fabric coming together at that corner to be sewn properly anymore.

The segments of the top layer are very simple, only 4 triangles each. Only the top has a wide border, the left, bottom and right have narrow borders. For my tent, I removed the red/yellow/yellow triangles on all five segments and replaced them with a clear plastic pentagonal skylight.

Before you start drawing and cutting fabric, I recommend you make a paper model using these patterns, including the borders, to familiarize yourself with the layout. Then, after the segments are all prepared, start assembling the top segments, then add the middle segments and finally the bottom segments.

This is me inside the dome, preparing the dome projection setup. This picture was taken with a fisheye lens; the dome is big but not that big...

And here is the projection rig: a 60 cm half-sphere security mirror and a video projector hooked up to a PC. Simple but very effective!

Many thanks to Paul Bourke for sharing his dome projection software and movie trailers! I had a great time playing around with various panoramic pictures.

Below you can see an outtake from a planetarium movie. Flying towards and then through the space station was incredible; people kept asking me to play it again and again.

Winamp in combination with the Milkdrop plug-in also drew a lot of attention. Even though the music visualization was not pre-warped to fit the dome, it still made for some very cool visuals.

So here we are, at WhatTheHack! I had lots of help raising the dome, thanks everybody! It was exciting to see the frame grow higher and higher, until it had reached its full height of 3 meters.

Then it was time to hang up the cover. It turns out that the elastic cords I used were too short! Fortunately, I brought lots of cable ties so that was easily solved...

The weather at WTH was very, very wet but the dome held up beautifully. The cover did not leak at all; there were only a few drops of water coming in through the ventilation holes during the worst of the rainstorms.

The tent is finished, at last! The whole thing is really quite big and unwieldy (about 4.5 m long), but all folded up and stuffed into a bag it is easy enough for one person to carry. The black vinyl anti-draft skirts that I added around the bottom add a few kilo's; I estimate that the total weight is about 20 kg now (excluding the 30 kg for the dome frame).

Sewing this dome shell is a lot of work! I've finished the top, with the skylight, all 10 main segments, and put the zipper and the awning in the front piece, for the doorway. All that remains now is putting the thing together!

Each vertex of the dome cover (there are 95) gets a suspension point, consisting of a little loop sewn onto a separate patch of tent fabric, which is then sewn onto the shell. This way, if the loop tears off, at least the main tent shell won't be damaged (or so I hope). I will thread a piece of bungee cord through each loop, which is then tied to the dome frame. This will make the suspension nice and springy, reducing the chances of anything tearing.

I found instructions for building a nice bamboo dome on Tara Landry's Desert Domes site. Though this has nothing to do with my dome tent project, I was curious as to how the finished bamboo dome would look. For less than €2, I bought two packs of 18 cm bamboo skewers from the supermarket and went to work. I used small metal wire bag binders to tie the crosses. The legs of the crosses are connected using masking tape.

As always with dome structures, the dome was quite unstable at first, but it got more and more rigid as it neared completion. The finished, 72 cm wide dome is strong and light and can be lifted by any vertex. The lengths of bamboo weave over and under each other, creating a nice, even tension throughout the structure (click the picture on the right to get a bigger image).

Since I'll need some light in the tent, I've decided to make the top pentagon of the dome cover from clear plastic. I bought a length of heavy, clear vinyl material also used in boat covers, which should not degrade or become opaque when exposed to the sun.

Unfortunately, the roll of plastic was not wide enough to make the entire skylight out of a single piece. Instead I've used two pieces, glued together with special soft-PVC glue, so the seams are still flexible. I took care to site the seams at the highest point of the cover, so as to make sure that no water can collect in them.

I've also spent some time familiarizing myself with the Pfaff 238 industrial sewing machine. This is the wonderful piece of machinery that I'll be using to sew together all the segments of the dome cover. It's almost 40 years old but still in perfect working order. It's strong enough to sew through several layers of tent fabric and a layer of plastic, something that I would not want to try with a common household sewing machine...

Now that the dome frame is all done, it is time for the next phase in the project: the cover. The plan is to sew a dome out of tent fabric, which will be suspended from the (91) vertices of the dome frame. This means that the tent fabric dome will have to be a little smaller than the frame; I decided to give it a 5.85 m diameter.

The tent will be composed of 15 segments of fabric: 3 layers of 5 segments each. The bottom layer's segments are the largest (16 triangles), the middle layer's are 12 triangles and the top layer's segments are only 4 triangles each.

To make measuring and drawing easier, I made five cardboard templates, one for each different type of triangle in the dome.

To lay out enough tent fabric to draw the segments, you need a lot of floor space. Thanks to bigmac for letting me use his (kids') playing loft, it was perfect!

Notice that the cardboard triangles have an extra purpose: you can sit on them while you move around on the tent fabric. This is a Good Idea, because you want to touch the fabric as little as necessary, to keep it clean and to prevent folds and creases while you measure and draw. The wooden beam was used to draw margins around the triangles, for the seams.

It took about 12 hours to get all the pieces measured, drawn and cut. Now I 'only' have to sew them together...

Still, the result looks very nice and I'm quite happy with it! There was plenty of interest from the neighbours, especially the younger ones.

I'm confident now that assembling the entire dome will not cause any serious problems. So now it's time to get to work on the next project: the dome tent cover.

Painting is almost complete; 250 struts are painted now. Many thanks to my sister for helping out! She did an excellent job painting all D (green), E (purple) and F (orange) struts.

All that remains now are the extra struts for the ventilation ports and doorway: only ten pipes in total; they can just be seen in the top of the picture. I should be able to get those done tonight, let everything dry and then we can raise the dome frame for the first time this Saturday!