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Post by Ron Walker on Apr 21, 2023 10:53:04 GMT -7
Please note that the following thread is from the very early history of the planetarium forum. Originally hosted where pictures were kept on imageshack and not with the main body of the forum. This changed soon after when the forum was moved. However the pictures from the first years were lost forever on imageshack. Somewhere I still have them and will try and find them and repost in the proper place in these threads. (Ron April 2023) Posted by: Ron Walker Aug 18 2006, 02:25 PM I've been bouncing ideas back and forth and have decided that I have to do something quickly just to be able to get back to my projection experiments. An inflatable would probably be the best way to go, but at a cost of between $5-$10K they are a bit out of my price point. Another drawback is the fact that the dome must make contact with the floor which could cause problems depending on the audience within the dome. The most positive aspect is that (made of the proper material) they can be used in a brightly lit room. The idea of a geodesic dome generates several problems. It takes a long time to set up and take down and the interior projection surface is not very smooth. Once the "lights go down" this might not be a problem but in my mind, the fewer sections the better. Also attachment of the projection screen to the geodesic structure could be a problem. The idea of a simple exoskeleton still seemed the best idea and I have discovered that I am not alone. As I am continually perusing the web looking for solutions to problems, I came upon this picture from a company in Sweden. imageshack.usThe beauty of this design is the open bottom allowing the audience easy ingress and egress. It does require a dark room to operate in and will not be perfectly circular. Each section will be flat between ribs very much like an umbrella but I believe less distracting then with a geodesic dome design. I will start by making a small six foot diameter trial dome and if all works out well I will build a 18 foot diameter one. From my estimates, I believe this can be accomplished for under $500. Time will tell. |
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Post by Ron Walker on Apr 21, 2023 10:54:10 GMT -7
Posted by: NeoDinian Aug 18 2006, 04:19 PM
Look for an Army/Navy surplus store near you... See if you can get a "Used" parachute. That would have the basic shape you need, but you would need to probably paint it or something. smile.gif
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Post by Ron Walker on Apr 21, 2023 10:54:32 GMT -7
Posted by: Ron Walker Aug 20 2006, 10:31 AM
Not at all sure how material would hold paint. I've painted material before for other projects and it has held up well until handled. Then the paint cracked and just looked bad. If the structure was permanent then that could be a viable idea. Since I need to be able to set up and take down, painting is not an option.
Also I'm not at all familiar as to how parachutes are put together. Which way the seams run and how would they appear under projection. How would I hold it up? Air pressure for sure, as that is how they are intended to work, but then the bottom from the spring line down would also need to be enclosed. How would I attach it to the exoskeletan if I didn't use air pressure?
I have looked on the web and found prices starting at $100 and up, $450 seems about the mid point norm. That's just about my price point for all materials of my design including the support structure.
I've purchased some materials. This first experimental dome might come out much cheaper then I had first planned. I'm building an eighteen foot diameter one made out of fourteen sections. The material (drapery lining) cost $169 and the 1/2" plastic pipe for the structure $62. A total of $231 so far, but that's all major purchases. I had planned a $500 budget for this particular project and it looks like it will come in for about one half that amount which is great. If it doesn't work well then I will not be too bent out of shape. Also, I am not considering this my final dome, just something that I can get up and running under.
The amount of material for the finished dome should weigh in at about 25 lbs., so the structure should have no problem holding it up. I'm making a small six foot diameter prototype first just to see how it all works. Should be the perfect dome for the small planetarium kits reviewed on this forum.
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Post by Ron Walker on Apr 21, 2023 10:55:01 GMT -7
Posted by: Launch Vehicle Aug 21 2006, 02:23 PM
Ron, try white lycra-reasonably lightweight, sews easily and holds it's seams well-and most importantly-stretches in all directions! Bit expensive, though. My 16-ribbed skeleton is inside, but the "bumps" are hardly noticeable. 'Works @ 100", not sure about larger diameters.-Bob
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Post by Ron Walker on Apr 21, 2023 10:55:25 GMT -7
Posted by: Ron Walker Aug 22 2006, 11:56 AM
Bob,
Any pictures, inside and out???
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Post by Ron Walker on Apr 21, 2023 10:55:43 GMT -7
Posted by: Launch Vehicle Aug 24 2006, 05:48 AM
It's been a long time since I last worked with it. But I'll do an APB search for my original pictures. If found, I'll scan them and post them.
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Post by Ron Walker on Apr 21, 2023 10:56:06 GMT -7
Posted by: Ron Walker Dec 6 2006, 11:47 AM
OK, time to get this project off the ground.
I'm going to try and relate to you all the trials and tribulations of building a dome for use as a planetarium screen. From the "front page" I will copy the following:
As hard as it will be for some of you to believe, a planetarium projector is the easy part. I'm finding that the real "pain in the neck" is the dome. Not that (once you understand the math) it's hard to figure out (on paper at least) and not that it's that hard to build a small test version (especially if your wife has some free time to sew it for you) but I'm just beginning to comprehend what a monster a decent size one is going to be. To all of those out there who have accomplished this without sending a big check to Spitz, I congratulate you (Ray Worthy, Gare, et.al.) My layout for the 18 footer is now finished and each segment will be about 13 ft long. Soon the material will be cut and then if I can find some free time (for my wife that is) this behemoth will be built.
I will take you all through all the steps that will be required to make this turkey operational. If it doesn't then I'll but a six pack and cry.... if it does work I'll probably do the same thing. Perhaps I should do it right now! biggrin.gif
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Post by Ron Walker on Apr 21, 2023 10:56:25 GMT -7
Posted by: SteveDurham Dec 6 2006, 12:21 PM
......Go for it!!!......We'll all be watching....and waiting.....
steve
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Post by Ron Walker on Apr 21, 2023 10:56:42 GMT -7
Posted by: Ron Walker Dec 6 2006, 06:03 PM
Your right Steve. I had a bunch of beer left over from my birthday, folks don't seem to drink as much as I remembered. I could start right now.....
Oh, perhaps your talking about the dome construction.....Sorry. I'll get to work on it.
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Post by Ron Walker on Apr 21, 2023 10:57:50 GMT -7
Posted by: Ron Walker Dec 18 2006, 05:07 PM
OK, it's time to start building.
First we must make the gores that the screen will be made out of. You can make as many or as few as you like. Just remember that if you do four you will basically have a box.
FORMULA FOR DOME PATTERN
1-Take desired circumference of the dome, divide that by the number of desired gores to find the width of each gore at the base of the dome.
2-To find your constant: 90 divided by 1/4 of the circumference equals your constant.
3-To find the width of the gore at intervals from the base towards the zenith:
a-Multiply the constant by the distance up from the base.
b-Find the cosine of that number.
c-Multiply the cosine by the width of the gore's base. The answer is your width at the distance up from the base.
An example: Since I wanted as large a dome as possible from the material I had, I went about this a bit backwards. Just follow along.
The material I found came in a roll 52 inches wide. I found that I needed two inches on either side of the gore to make the support collar for the gore. Thus each gore could be 48 inches at the base. I decided to use a total of 14 gores as this made as large a dome as I could build in the space I had available. Thus I am starting the above calculation with a circumference of 672 inches.
As in the above calculation:
1-Desired circumference 672 inches. Total number of gores 14. Thus 672 divided by 14 equals a 48 inch base for each gore.
2-90 divided by 672/4 equals 0.5357 which is my constant for the above dome.
3-a-0.5357(40)=21.428
3-b-cos21.428=0.93088
3-c-0.93088(48inches)=44.6822 or 44 11/16 inches.
If you followed that at all you would understand the each gore has a base that is 48 inches wide and that at a distance of 40 inches up along the gore toward the zenith of the dome, each gore would have a width of 44 11/16 inches. Now it is best to make a template and then cut the material for the gores from the template. Be sure to allow the extra material on both edges to make the support collar. We made calculations for every two inches along the gore's 1/4 circumference of the dome.
The is an example from the calculations for my large dome. Before this was tackled we made a small baby dome to make sure we were doing everything right. Calculations and pictures will follow both on the experimental dome and the full size one as construction begins.
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Post by Ron Walker on Apr 21, 2023 11:29:57 GMT -7
Posted by: Ron Walker Jan 12 2007, 03:06 PM First to make a paper template for one of the gores (there will be 14 in this dome design.) imageshack.usAt the left end (horizon line) calculations were made for every two inches. When the curve became more and more critical as we move right towards the zenith point, calculations were made for every inch. The extra material on the outsides of the gore lines is for sewing the gores together and making "loops" to attach the dome to its support structure. |
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Post by Ron Walker on Apr 21, 2023 11:30:33 GMT -7
Posted by: Ron Walker Jan 14 2007, 03:02 PM The outside support structure must itself be supported at two points. The top of the dome is first. imageshack.usThis top central core was cut out of a piece of 2X6 scrap wood. I first drilled holes for 1/4 inch diameter wooden dowels, which were cheap and appeared strong and would also bend the required 90* in their three foot length. Now, as you can see, the spines are actually 1/8 inch steel rods. imageshack.usThis picture shows the 1/4 inch wood dowel compared to the 1/8 inch steel rod spine. As with all good intentions (and experimenting) I found the 1/4 inch wood dowels developed a problem. imageshack.usSo much for that idea. Not to waste the top support core, I just flipped it over and drilled smaller holes for the 1/8 inch steel spines. Now, you will note that the dome material seems to be a bit "wrinkled" between supports. This is because the tension is incorrect as the cloth loops in which the support spines are enclosed were originally sewn for a 1/4 inch spine and not an 1/8 inch spine. imageshack.usYou can see in the above picture the smaller 1/8 inch spine moves to the back/top of the material loop. If I pull the loop tight (so that the spine is in contact with the bottom of the cloth loop) a large percentage of this wrinkling goes away. An interesting point is that when used as a projection surface for stars (as in the photos under the "HomeStar" review) even this large amount of wrinkles don't get in the way of the image. The spines must also be supported at the bottom of the dome at the horizon (or spring line) and this I did with sections of wood. Dividing the circumference into 14 equal segments and angling them at 22 1/2* each to get a basic equator. These were screwed together so as to give the support the rigidity needed to support the spines. imageshack.usThe next two views show the entire dome from top and bottom. imageshack.usimageshack.usAs you can see, the dome is self supporting and can be lifted and supported from any point on the two main supports. The opening at the top will be covered with a circle cut from white poster board which I was going to cover with the same material but now am not so sure that it will be necessary. The pictures that I took of the "HomeStar" projections were with this dome hung from a hook attached to the top 2X6 wood core. I will probably do the corrective sewing on the cloth gore rings so to remove most of the wrinkling of the material. The results are good enough to not only use this small dome as a portable projection dome, but to give incentive in the construction of the larger 18 foot one. I have already built the top core into which the spines (1/2 inch plastic water pipe) will be inserted. They seem to be able to bend the required 90* in their 14 foot length. Hopefully they will not suffer the same fate as the 1/4 inch wood dowels. imageshack.usimageshack.usThe saga of the large dome will continue. |
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Post by Ron Walker on Apr 21, 2023 11:30:55 GMT -7
Posted by: Launch Vehicle Jan 15 2007, 08:22 AM
Wow, Ron, you the man! The 6' dome looks like it was made by a professional "dome builder." You're plowing new ground here and everyone is waiting to see how you scale this puppy up! Good luck!
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Post by Ron Walker on Apr 21, 2023 11:31:13 GMT -7
Posted by: SteveDurham Jan 15 2007, 08:47 AM
Ditto.......
AND, being the "Staff" of Marge's Monograms has led me to become quite familiar with a sewing machine.....that's an "FYI".
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Post by Ron Walker on Apr 21, 2023 11:31:31 GMT -7
Posted by: Ron Walker Jan 15 2007, 12:57 PM
You guys are much too kind! Actually 90+% of the credit goes to my wife Julie. She not only pulled out her trusty scientific calculator, which turned what could have been an ordeal into a simple chore, but pushed me away from the sewing machine and made the nice even stitching that I could never have made.
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