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Post by Ron Walker on Apr 21, 2023 12:04:22 GMT -7
Posted by: Owen Phairis May 13 2008, 10:22 AM Tent Dome... As many of you know I started out with a traveling planetarium show that used a 20 foot by 20 foot tent. I used the Goto S-2 planetarium projector, slide projectors, robot, etc. Recently I got the tent parts out to see if I could reconfigure it for a smaller size. I was able to make a 15 foot by 15 foot tent. This should be able to fit in my building or other confined spaces. It was my experience, that even though the tent is sort of more like a pyramid at the top, in the dark it did not detract very much from the star show. I have attached a picture showing the 15 foot top section assembled and the telescopeing legs inside. Owen Planetarium Projector Museum ( www.pictorialism.com )
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Post by Ron Walker on Apr 21, 2023 12:04:53 GMT -7
Posted by: albert Apr 15 2009, 11:25 AM QUOTE(Ron Walker @ Dec 19 2006, 02:07 AM) * 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.
Hello Ron,
may I ask where you found the dome formula? I want to start on a model dome having a diameter of 3 feet, and I spent the afternoon with a pocket calculator doing the calculations for it. I will try Depron foam boards, the ones small RC planes are made of.
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Post by Ron Walker on Apr 21, 2023 12:05:14 GMT -7
Posted by: Ron Walker Apr 15 2009, 01:09 PM QUOTE(albert @ Apr 15 2009, 11:25 AM) * Hello Ron,
may I ask where you found the dome formula? I want to start on a model dome having a diameter of 3 feet, and I spent the afternoon with a pocket calculator doing the calculations for it. I will try Depron foam boards, the ones small RC planes are made of.
Sort of came up with it on my own (with my wife's help and her scientific calculator). That's why I made the small one first as I didn't trust my mathematical skills. blink.gif It does work as you can see from early posts on this thread.
Please take pictures.
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Post by Ron Walker on Apr 21, 2023 12:05:44 GMT -7
Posted by: albert Apr 16 2009, 11:51 PM QUOTE(Ron Walker @ Apr 15 2009, 10:09 PM) * Sort of came up with it on my own (with my wife's help and her scientific calculator). That's why I made the small one first as I didn't trust my mathematical skills. blink.gif It does work as you can see from early posts on this thread.
Please take pictures.
I really admire you for that, I could not do that. Perhaps you can for the better understanding of it elaborate a little how you came up with it? The cosinus bit and the constant?! Black art for me. BUT The formula works, since a small 3 ft. dome is taking shape at this moment in my workshop. Pix will follow if I dont throw it out the window before. The cutting of the pieces is not the real hassle, putting it together is a hair puller. Do you have any idea how to make the central circle in the Zenith? And incorporate that in the pattern? I thought I could do this on the fly but ....on a "solid" dome the bending of the pieces to the inside is the problem. I found out that the smaller the model the greater the need for precision.....you would almost need a laser cutter to come up with anything REALLY precise. I have a razor blade and a wood saw. sigh. huh.gif But I got filler putty. But I'll get it to work at the end It will only take longer.
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Post by Ron Walker on Apr 21, 2023 12:06:04 GMT -7
Posted by: albert Apr 17 2009, 12:16 AM I made a wooden ring for the base, pieced together from several parts to make best use of the wood I had lying around. The gores are made from Depron, foamboard without the paper on it. (Insulation material, 4 mm thick)
Here the pieces are glued in place and stick out like the spikes of a kings crown.
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Post by Ron Walker on Apr 21, 2023 12:06:20 GMT -7
Posted by: albert Apr 17 2009, 12:23 AM Then I took some books and piled them up in the center for the desired height. Added some more books on top... this shows that your formula is working correctly.
At least it looks dome-ish.
I think I will make apost with a circle of foamboard on top and the required height, attach the gores to that and then close the gaps by adjusting th individual pieces. I am glad I did not make the thing bigger. It has 24 sides, since I did not want to have a 12 sided polygon.
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Post by Ron Walker on Apr 21, 2023 12:06:42 GMT -7
Posted by: Owen Phairis Apr 17 2009, 08:40 AM QUOTE(albert @ Apr 17 2009, 12:23 AM) * Then I took some books and piled them up in the center for the desired height. Added some more books on top... this shows that your formula is working correctly.
At least it looks dome-ish.
I think I will make apost with a circle of foamboard on top and the required height, attach the gores to that and then close the gaps by adjusting th individual pieces. I am glad I did not make the thing bigger. It has 24 sides, since I did not want to have a 12 sided polygon.
Nice work Albert,
May I ask what kind of experimental star projectors do you planning on using it with?
Thanks,
Owen -
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Post by Ron Walker on Apr 21, 2023 12:07:08 GMT -7
Posted by: albert Apr 17 2009, 10:36 AM QUOTE(Owen Phairis @ Apr 17 2009, 05:40 PM) * Nice work Albert,
May I ask what kind of experimental star projectors do you planning on using it with?
Thanks,
Owen -
Hi Owen, I want to use a voodoo doll with a light shining out of it to test the true meaning of pinhole projection. wink.gif ... No...the first purpose was to see if the dome formula works and can be applied to a "solid" structure, not a cloth dome. I can confirm it is a workable thing. Could be enlarged and might be a lot easier than to do a geodesic dome. If you make it from a material that can be sanded and painted, even larger goofups may be covered up...making a miniature is always a good idea if one wants to evaluate the difficulties of a project. my second idea is to test M. Yves Lhoumeau's adapter for a fisheye lens to use with a video projector. It can be found elsewhere on these pages. since I have the necessary lenses in my stock, it will cost nothing to give it a try with stellarium as the software. I also think I will try to airbrush the inside with a light grey tone to see if that works better with video projection. The foamboard has a "glint" to it anyway and is less than ideal as a surface for projection. I havee put the dome together today and I'll let it sit and dry for a while before I continue.
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Post by Ron Walker on Apr 21, 2023 12:07:31 GMT -7
Posted by: Ron Walker Apr 17 2009, 12:39 PM QUOTE(albert @ Apr 16 2009, 11:51 PM) * I really admire you for that, I could not do that. Perhaps you can for the better understanding of it elaborate a little how you came up with it? The cosinus bit and the constant?! Black art for me. BUT The formula works, since a small 3 ft. dome is taking shape at this moment in my workshop. Pix will follow if I dont throw it out the window before. The cutting of the pieces is not the real hassle, putting it together is a hair puller. Do you have any idea how to make the central circle in the Zenith? And incorporate that in the pattern? I thought I could do this on the fly but ....on a "solid" dome the bending of the pieces to the inside is the problem. I found out that the smaller the model the greater the need for precision.....you would almost need a laser cutter to come up with anything REALLY precise. I have a razor blade and a wood saw. sigh. huh.gif But I got filler putty. But I'll get it to work at the end It will only take longer.
You expect me to remember what I did to come up with that.....that would take hours to re-think. You would need a mathematician for a proper answer. Anyway, hopefully this will help.
Since we will be laying out dimensions on flat material we want this to be somewhat linear. The length of any gore is 1/4 the circumference as well as 90 degrees of the circumference. Wanting to be able to work in whatever dimension one would like (inches, centimeters, cubits) we work out a constant by dividing 90 (degrees) by 1/4 the circumference (which is the same distance as that 90 degrees but in a measured distance based on the size of the dome and in your chosen dimension.
Since each measurement as we move up toward the zenith is basically a circle or circumference at a given latitude and we all know that the circumference becomes smaller and smaller as we head toward the zenith. Up pops trigonometry. If we assign a cosine of one for the circumference at the spring line (0 degrees latitude) then the calculations for any degrees toward the zenith (90 degrees) can with the use of the constant be calculated in the measurement of choice. Thus rather then using degrees up from the spring line, we can now use actual dimensions. huh.gif
Does any of that make any sense??? blink.gif
There are other ways to do this as finding the entire circumference at any given degree up from the base line and then divide by the number of gores, but I found this the easiest to make one gore and then just duplicate.
Now that I have you totally confused......
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Post by Ron Walker on Apr 21, 2023 12:07:54 GMT -7
Posted by: albert Apr 18 2009, 02:10 AM blink.gif blink.gif blink.gif .... I'll have to print that out....Take a deep breath...disconnect the phone....lock out the cats....go into a dark corner...with a can of beer...and mull it over. But I'm sure the light will go on! Maths were always a big bugaboo to me... unfortunately.
Thank you Ron ! I'll try to "grok" that.
Albert
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Post by Ron Walker on Apr 21, 2023 12:08:12 GMT -7
Posted by: Ron Walker Apr 18 2009, 11:13 AM QUOTE(albert @ Apr 18 2009, 02:10 AM) * blink.gif blink.gif blink.gif .... I'll have to print that out....Take a deep breath...disconnect the phone....lock out the cats....go into a dark corner...with a can of beer...and mull it over. But I'm sure the light will go on! Maths were always a big bugaboo to me... unfortunately.
Thank you Ron ! I'll try to "grok" that.
Albert
I think it will take more then one can. I am not much better at math but am fairly good at reasoning things out. The entire equation is just based on the cosine of the angle as one moves from 0 degrees (the horizon) to 90 degrees (the zenith). This then makes it easy to get the circumference "slice" at any degree up from the horizon. Then the number of gores must be taken into account. I just wanted to get it in a form that would be easy to use by just plugging in numbers. Someone who really understand math can probably sum it up in one sentence.
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Post by Ron Walker on Apr 21, 2023 12:08:45 GMT -7
Posted by: OdedK Feb 3 2015, 08:10 AM Hi Ron, I'm writing this message from Argentina, I purchased a 10 meters geodesic structure some time ago and I'm truing to find ways to build the projection dome inside. I was reading all the messages and they are very helpful, but since the last message was posted many years ago...I wonder what happened since then and if you have found any new solution to this manner.
I have attached a picture of the geodesic dome and you can see the inflatable dome inside that I still use for teaching
I would appreciate any suggestions best regards
Oded Kindermann Astrojujuy - Mobile Planetarium Jujuy - Argentina
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Post by Ron Walker on Apr 21, 2023 12:09:29 GMT -7
Posted by: Ron Walker Feb 3 2015, 10:32 AM Hi Oded and welcome to OCP.
For me, a lot has happened since this thread. Back then I was looking to build a six meter dome for us with a Spitz A3P that I was rebuilding at the time. I was looking for something that could be put up and taken down easily as the space I had to put it up had other uses. It was to be made of sixteen gores (to get the most bang for the buck) and with my wife's help, built a four gore section. It was constructed out of drapery lining material and weighed a ton. This was not going to be something that could be put up and taken down at will. This was not going to be an inflatable dome but one supported by plastic pipe on the outside.
It was also about this time that I moved on to my Minolta projector and decided to build a more permanent structure as it required a 9.1 meter dome. I did a geodesic dome structure as it was constructed out of small sections of materials which allowed my to basically build it myself. I tried several experiments to get a perfectly rounded interior but all failed for one reason or another. I finally just decided to put up drywall triangles and hope the image wouldn't be distorted too much. There are five coats of drywall mud at each junction as well as along each edge of the triangles which takes helps give the interior a more rounded and some like appearance. For the projection of stars this works extremely well and I plan to experiment with all sky video projection soon.
The idea solution would be some kind of actual interior dome but the old wallet is basically empty. I have not received any comments about the dome as it is now so I really doubt I'll do anything more with it. Being my own worst critic I find that, if I am happy with it, everyone that visits is happy as well.
It is interesting that I have generated absolutely zero interest in a "I come to them" kind of portable planetarium and it is so nice to just go out a flip a few switches and be up and running in a minute or two. The biggest constraint is waiting to get ones eyes totally dark adapted for those sixth magnitude stars and the Milky Way.
What you are doing right now appears to work for you. Making anything like a negative pressure dome would be a nightmare to set up and take down. Attaching a blow up dome to the interior of your geodesic structure would also be a pain in my mind. I would imagine you use the geodesic dome as a protection against the elements for your inflatable dome and it works well. The old adage, "If it ain't broke, don't fix it", comes to mind.
The only possible change I can see would require the screen supported by the geo framework and hanging inside but it would still need to inflate it to keep it smooth and round.
What kind of changes would you like to make?
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