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Observatory Central > Planetarium Forum > Planetariums as a hobby > Planetarium Domes ~ design, construction, and building
natehieter
I recently built a 4m "2V" geodesic dome on a 20degree tilted base at a local elementary school. It was well received and everybody thought it was spectacular..... except me!

The triangle grid and the way the scenes "folded" as they crossed from triangle to triangle seriously undermined the experience. Sadly, we remain severely budget limited at the present time so an inflatable Go-Dome or a fiberglass one from Astro-Tec are not possible "right now".

I am considering DIY alternatives involving polycarbonate "gores" and fiberglass for rigidity. I would use plywood strips on-edge to provide the skeleton, a roll of polycarbonate to make gores for the skin, and then coat the dome with fiberglass to provide structure. Depending upon whether or not I have to transport it I would do the complete dome or break it into quarters.

Aside from the roll of polycarbonate (which I think I can get from an industry contact) most of the materials should be with the realm of a DIY project. There are few locations with sufficient ceiling height. Depending upon community support I might shoot for a small structure near the school.

I am confident that I will have PLENTY of skilled volunteer labor. The challenge has been to find materials and components that will not break the bank. Unfortunately, that has translated into disqualifying any major components.

I welcome feedback and insight on the proposed design and recommendations on size. We are still in the "dream" phase so there is plenty of time to change the plan.
Ron Walker
Hi Nate and welcome to OCP.

I can understand your disappointment with a 2V dome and the angles that would make projection problematical.

http://www.desertdomes.com/dome2calc.html

I think you would be much happier with a 4V dome as it would make a more rounded surface.

http://www.desertdomes.com/dome4calc.html

The big question as you have already noted is if the dome would need to be moved from place to place. You might want to consider a cloth dome supported on the outside with gores made of 1/2 in schedule 40 plastic water pipe. This will be easily transportable should the dome require this.

So much is dependent on size so I guess the first question should be, "What diameter do you want the dome to be?"
natehieter
I'm considering a 5meter minimum. Ideally, I'd get a semi-permanent location and shoot for 7m, but 5m is where I'll likely end up.

I used 168 2in binder clips with the 40 ~4ft triangles. If I go up to 3V..... that's a crap ton of binder clips!

Really, the main problem I forsee is that the edges of the triangles do not reflect light well resulting in a visible grid. Going to 3V (or 4V!) will give me a nice curve, but also increase the number of dark lines.

I'm intrigued by the cloth idea. Would hanging the cloth accentuate the seams? Or is "stretchy" material a possibility? Would I use a muslin-like product that gets painted?

natehieter
A couple pictures of me and my kids in our current setup (spherical mirror projection)
Ron Walker
I moved this topic because it is about building a dome rather then building a video projector. Hope I don't confuse anyone. blink.gif
Ron Walker
QUOTE(natehieter @ Mar 10 2012, 07:04 PM) *
I'm considering a 5meter minimum. Ideally, I'd get a semi-permanent location and shoot for 7m, but 5m is where I'll likely end up.

I used 168 2in binder clips with the 40 ~4ft triangles. If I go up to 3V..... that's a crap ton of binder clips!

Really, the main problem I forsee is that the edges of the triangles do not reflect light well resulting in a visible grid. Going to 3V (or 4V!) will give me a nice curve, but also increase the number of dark lines.

I'm intrigued by the cloth idea. Would hanging the cloth accentuate the seams? Or is "stretchy" material a possibility? Would I use a muslin-like product that gets painted?


If the dome needs to be portable then you become limited in design as you have probably found. Most ideas work best with a conventional horizon and not a tilted dome. A rigid dome or a rigid support structure would be required for a tilted dome.

If you haven't yet I will refer you to: http://www.observatorycentral.com/index.php?showtopic=249 where we talk about making a dome out of a number of gores. Like geodesic triangles, gores will tend to form ridge lines as well. Some people have used tape of the proper color to cover the seams but then you might not like the wider look of he seams. The more gores the smoother the dome surface but the more time consuming the set up and take down. For a portable smooth dome surface you will need to build sections out of curve formed material (plastic) or (what most everyone else uses) a blow up dome. A variation on the blow up dome is the "negative pressure dome" which would allow on open bottom without walls.

As for gore cloth material, the best that I have found is "drapery lining" which is available in "blackout" basically lightproof but very heavy three layer, to simple single layer but heavier then say bed sheet material. Both are available in white and I would imagine could be painted a light gray for video type projection but I doubt it would take very many setups before the paint would start cracking. It might actually come in a light gray color.

When projecting stars one can get away with a lot of seams but not with a video image. So much depends on what is more important for your presentation and more importantly, your budget. But then I remember seeing an Omnimax film at the museum in San Diego a few years back where they projected the image onto a geodesic structure which was not at all impressive. This did not keep them from charging substantially for the experience. My understanding is that they installed a Nanoseam Spitz dome but "fool me once...."
Ron Walker
QUOTE(natehieter @ Mar 10 2012, 07:15 PM) *
A couple pictures of me and my kids in our current setup (spherical mirror projection)


Great looking family!

Would love a detailed description (with pictures) of your video setup and any problems you encountered in design and construction.
natehieter
I used the very well documented plans on the WWT site:

http://www.worldwidetelescope.org/Docs/wor...lanetarium.html
Ken Miller
I'm pretty happy with the overlapping gores design that I use at home and in the new dome that I have built for the Maker Faire. I do video projection, and this works well for getting a spherical surface. Also there are less fire code issues with using hardboard as opposed to cardboard. I have discussed it several times on this forum. The idea was first suggested by Charles Jones, and described by him on this forum. My home dome is 9 ft diameter, the Maker Faire dome is 6 ft diameter, and Charles' original dome is 11 ft diameter. I posted gore dimensions on the Yahoo Small Planetariums group. I can provide links and more discussion here if it would help.
ltkhoover
Hi Nate,

Here is the build thread on my cloth dome http://www.observatorycentral.com/index.php?showtopic=3533 . I did a 10 gore dome as an "experiment" thinking I would do a 20 gore dome if it worked. I was so sick of sewing at the end that I have not mustered up the energy to do a new one yet.


If you go the cloth route, I would suggest doing at least a 20 gore dome. I would sew up two 10 gore sections and then sew the two sections together. If is amazing how much patients is required to push a bunch of gores through the machine....



I have an idea on how to use foam sheeting to create a self supporting, relatively inexpensive, dome. I will marshal my thoughts together as well as the experiments I have done and post something on it in the next couple of days.



Lee
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