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DIY Torus nearing completion

2034 Views 11 Replies 5 Participants Last post by MC Maniac, Feb 27, 2005

Semisentient

Discussion Starter · Feb 21, 2005

I'm in the final stages of completing a Torus style compound curved screen and thought I'd post about some of the trials and tribulations I have gone through to get to this point.

All in all it was a fun project. All I have left to do is actually staple on the screen material. The material is the Vutec PearlBrite 3.1 .I am hoping there will be no surprises! When I did a quick test with the material it didn't seem to have much gain, but I'm hoping that is because it wasn't tensioned. While testing the material I noticed that quite a bit of light passed through it so blacking out of the inside of the box would be very important. I ended up lining it with black velveteen just to be safe.

The screen itself is 108" by 54". The string method for determining curves came up with a pretty deep horizontal curve, so going by posts of other people who have built these, we compromised with curve depths of about 8.5 and 3.5 inches for H and V.

To control the screen depth I am using a limit switch to modulate a fan which draws a vacuum on the inside of the screen. This should work well along with the various voltage settings of the wall transformer. Since the idea is that the switch is put in such a position that when the screen is at the proper depth, it will hit the switch, turning off the fan, I wanted to find a switch with a very soft touch. Easier said then done! I did eventually find one.

For the sake of adjustment and replacement I made sure the limit switch, fan and wall transformer jack are easy to get to. The last thing I wanted was for the switch or something to fail with no way to get to it!

The hardest part of the project, other than finding time to work on it was dealing with the Canadian winter. Because of the size of the thing I had to build it in my garage (this one is not going into my theatre...). It's amazing how many materials such as glues, caulkings and paints say not to be used under 5 to 10 degrees Celsius. I must have a great wife, 'cause she let me keep the thing in our foyer for a week or so.

Anyways attached is a pic of the screen box sans screen material.

James

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Ericglo

· #2 · Feb 21, 2005

James,

I can't wait to see your finished product. How much material cost minus screen do you have into this project?

Ericglo

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Semisentient

Discussion Starter · #3 · Feb 21, 2005

Quote:

Originally posted by Ericglo
James,

I can't wait to see your finished product. How much material cost minus screen do you have into this project?

Ericglo

Hmmm... I was keeping a spreadsheet, but can't seem to find it... I would guess roughly $125 - $150 not including screen material.

James

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Ericglo

· #4 · Feb 21, 2005

James,

May I ask how hard it has been to build and how much time you have invested?

Ericglo

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garyfritz

· #5 · Feb 21, 2005

For a curved or toroidal screen you want a very high-gain surface, since lower-gain materials disperse the light too much. The dispersed light can then spill onto adjacent screen surfaces and wreck your contrast ratios.

The PearlBrite has a 3.1 gain. I dunno if that's high enough or not. I know of people who made their curved screens out of straight Rusto Aluminum and are very happy with it.

The only specs I can find on the Vutec site say the PearlBrite has a viewing cone of 140deg. But they say their BriteWhite is 180deg, so obviously they have a very loose definition of "viewing cone." Hopefully the reflection at low angles will be small enough that it won't spill onto the nearby surfaces.

Have you checked to see if the PearlBrite is flexible enough to work well in an air-tensioned torus application?

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ender611

· #6 · Feb 21, 2005

Wow semisentient, that is quite the project. I hope that pearlbrite is air tight. You pull this off and you'll be a DIY guru. Imagine the cost of trying to buy something like that.

Not that I'm doing a torus yet but thinking about allot of things lately has this potential.....Using those fiberglass posts ( landscaping, snow fence, tent posts ) for the screen border attached to the screen with grommets and rope. Fit this inside a box with wire or hardware every six inches pulling the post straight with the edges of the box. Then use wire or adjustable hardware to clamp onto the post every six inches from behind to the back of the box. Then by tightening/shortening the from behind lengths or bolts as you go towards the center the fiberglass posts will bend taking the screen with it.

edit:

guess the fiber glass posts aren't even necessary, just tie the back wire and side wire to the same grommet and keep adjusting both.

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Semisentient

Discussion Starter · #7 · Feb 21, 2005

Ericglo,

The hardest part has been figuring some things out as I go. Only basic woodworking skills are needed. This is good 'cause those are the only skills I got! It's hard to say how many hours as I had to break it up to small chucks due to losing a bunch of weekends to a work project. Were I to build another (which I will be soon) I figure it will take a few solid days.

garyfritz,

This screen is based on Atom, another forum member's screen. He used the same material and it looked great! The contrast was very impressive so I am guessing light dispersion is not an issue.

ender 611,

The pearlbrite is air tight. It's very much has the look and feel (and smell) of a shower curtain or pool liner. Some other people who have built these screens ended up having to drill holes in their boxes because it was all too air tight!.That method you are describing is pretty original. I would recommend the method I am using as it is tried and true...

James

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garyfritz

· #8 · Feb 22, 2005

ender611, seems like your method could produce the right shape around the borders, but there's nothing to force the curve in the middle of the screen. You really need something pulling the screen backward.

But you got me thinking. What if, instead of going to the trouble of building the box with the fancy curved edges, you just support the screen with wires along the edge like you suggest, and attach the wires to posts at the corners. Then make the thing airtight and run the fan behind it. Same concept of a fan-drawn torus, but maybe a simpler and lighter construction method?

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ender611

· #9 · Feb 22, 2005

You're right, I could only hope to take care of the curve of one axis with those wires and the grommets would have to be almost overlapping to make that smooth. With semisentient's box at least the screen is in a good starting position. But even starting from there when the fan sucks the middle back this originally rectangle screen is going to want more length in the middle compared to the edges both horizontally and vertically.

If this Atom hadn't already acheived this I'd be skeptical that it could be pulled off without a little bit of wrinkling happening in spots as it pulls the middle sections tight ( will there be any ability for the screen to move..bungee style ). Even getting that screen to lay proper in the box seems a challenge without compressing some parts of it.

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Ericglo

· #10 · Feb 22, 2005

ender611,

Do a search on Torus screens both here and in the CRT forum. There have been a couple of guys who have built these screens with great success.

I think what you guys are trying to do sounds harder than building a suction box. I was thinking that one could use blackout cloth or similar and paint it with a high gain formula for an inexpensive screen to mount to a Torus box. By Semisentient's calculation that would give a total cost of around $200. I have also thought of a hard Torus. One could use a laminate glued to say seven vertical slats of the correct curve. As long as the curve isn't to deep, it should not be a problem for the laminate. I have a small piece of Wilsonart that I was able to do this with. Just an idea.

Here is Armstrr's Torus http://www.avsforum.com/avs-vb/showt...hreadid=467141

Ericglo

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