Question about collimated display systems.

[mikesblack]

Hi Wayne,

How wide, radius and degrees vertical and horizontal will the final mirror be?

Given that material can be found at 55 inches, could you remind me what limits we face and in my case assuming a 7 foot radius curve and 40 degrees vertical( ideal).

I have been thinking about using either thin plasic packaging tape or mylar tape to join 2 sheets of mylar. I have experimented with small pieces and have found good results. The tape is applied on the back of both pieces and carefully lined up and smoothed on.

Love to hear your thoughts on that.

Hope you and Gene are well.

[geneb]

mikesblack: I suspect that when you try to stretch the mylar under vacuum that it's going to distort at the seams.

The current setup gives us an 8' diameter mirror. The framework provides 180 "real" degrees of mirror plus the extra we get for the "ears". If I remember correctly, this gives us 180 degress of "perfect" view with some space on either end that provides "usable" mirror which then degrades into "funhouse mirror" at the ends.

If you look at this picture: http://www.fotothing.com/photos/492/...50212c_ab4.jpg you'll see the "ear" that we keep referring to. On their setup, they've trimmed the mylar back from the full curve of the ear. Our mirror will cover it completely because of how we're attaching it.

The photo that really got my attention was this one:
http://www.fotothing.com/photos/115/...c9a914_9f6.jpg
If you zoom in on it you can see that the mylar is being brought into position in a fashion very similar to how a shower curtain is hung. You can also see two black parallel lines at the top edge of the mylar. This makes me wonder if there's something sewn into the material - maybe a reinforcing strip or something like a sail bat?

I suspect that band is some kind of reinforcement for the method they're using to hold the mylar in place. I'd love to talk to the guy on the ladder.

That image shows some of very interesting details - one an approximate depth of the frame. You can see it in the bottom right hand corner of the image. Another detail is what appears to be the vacuum port at the back of the framework in the center. I'm not sure why there is two - volume maybe?

In the lower LEFT corner, you can see what looks suspiciously like the paper that would cover double-sided tape! It looks like the repeating logo thing done on some brands of 3M tape. The tan color above it may also be some kind of tape backing. If you look closely, you'll see a "hump" in the material (right near the left edge of the image). I've seen a similar effect in double-sided tape backing when it's applied around a curve... I bet if we could see the "ear" on that end, there would be a line of that material going straight up to the top edge of the framework.

In this image:
http://www.fotothing.com/photos/88d/...c2e7fd_15d.jpg

...HA! I was right! If you look at the bottom of the image, just to the right of the ladder, you can see a bit of adhesive covering peeking from behind the mylar and directly to the right of that there is an obvious band where the mylar is stuck to the tape! I don't see any evidence of the reinforcement band on the bottom, so that may have only been done in order to lay the mirror in place before they expose the adhesive behind it. In fact, if you look to the top of the mirror directly above the band I just mentioned, you can see extra material folding forward of a line that appears to have attached it - I think at this point in the process the worker is working from right to left - you can see how the mylar is "stiffer" on the area on his right. He's in transit on the ladder by the position of his foot, but I don't know if that's going up or down. The area to his left is still being supported by the top edge, so there may be some kind of rail up there that we can't see - maybe for removable clips that are attached to that reinforcing band?

This weekend I'm going to try to get the base platform built and painted. This is what the table will attach to and then the mirror chassis will attach to the table.

We're going to build a new screen - more in line with the current design. The trick is going to be building a jig in order to cut the foam with. I don't expect it to be much of a problem though. Anything that keeps my fingers way from that table saw blade makes me happy. The last one we built was something like 40+ cuts on the table saw with the blade run all the way up and my fingers about an inch away from it. I was really, really glad to be done with that particular part of the project. I had to be lucky every single time. The table saw only has to be lucky once.

g.

[geneb]

I just did a bit of research on the CAE 7000 Series simulator that those pictures show - it has a FOV of 200 degrees wide by 43 degrees high. The mirror that Wayne & I are building is really close to that 180-190 (or so) wide and 40 high. Not too shabby for a couple of sim geeks.

g.

[wledzian]

Mike,
Without digging into interference issues between cockpit and display geometry, I can squeeze about 115° out of the full-height mirror, with possibly an additional 10°-15° usable in each ear, using a 1" margin. This does not account for the dead band, which probably eats up about 5° at the top and bottom, leaving ~30° usable. If I increase the vertical FOV to give a 40° usable area, the full-height section drops all the way to 30° horizontal, perhaps 70° total including the ears.

[mikesblack]

Thank you Gene and Wayne. Appreciate the response.

What do you guys think of my idea for joining mylar in order to get full width?

[wledzian]

The seam will be locally stronger, and will therefore stretch less. This will most likely produce some fairly severe distortion.

[mikesblack]

I was thinking the same thing, but figure it may be worth the experiment. I'll let you know what I find.

BTW Do you know who manufactures the mylar for CAE and the other sim manufacturers?

[tomenglish2000]

Hello all.

I was talking to a friend who visited the install of one of these. He says that the back of the dome is a material like felt or fine carpet which is either attached to a solid structure or has been treated to be stiff enough on the back to hold the spherical form. Because its carpet/felt it isnt air tight and allows air to be drawn through it. Looking at the pictures I think he might be correct, it certaintly looks like it has hand prints in it like you would find on the top of a pool or snooker table. He didnt mention how the mylar was attached to it but I think we can see it in the pictures and figure it out.

Please look closely at this photo http://www.fotothing.com/photos/115/...c9a914_9f6.jpg that Gene also linked to.

Around the top and bottom of the black dome area where the mylar gets attached if you allow your eyes to follow it around the curve I believe it is sloped backwards from the black dome. Some of the patents linked earlier in the thread (if memory serves, perhaps they were on one of Mike's tutorials) showed methods for attaching the mylar. One showed the use of material to for a uniform curve around the top and bottom of the mirror so that the mylar isnt going around a sharp angle and this makes sense with the picture's sloped back attachment area.

So contrary to Gene I think the material is folded back and not forward in the second picture.
http://www.fotothing.com/photos/88d/...c2e7fd_15d.jpg
I also think he might be working out from the centre to the sides.

So my interpretation is this. The mylar is placed in the dome shape. Note that there is no measuring equipment visible in any of the photos (tape measures etc) so the black lines on the top must make sure the mylar is positioned correctly. As the guy moves out from the centre he removes a bit of the backing paper from the tape (as can be seen at the bottom in the second picture, there is a tail of the brown backing paper peeking out from under the mylar) and he sticks it down on using the black marks for guidance. The thing I cant figure out is how he knows where to stick the bottom, there are no black marks that I can see, surely it has to be more scientific than just guessing when the mylar is loose enough.

In the second picture at the very top right you can see the black marks for the top but on it's back there is no evidence of reinforcement.

Anyone have any thoughts?

Tom

[andyb]

I'm not sure of the exact supplier (it was 10+ yrs since I was playing with Mylar) but I do recall the manufacturer was in Eastern Europe (narrows it down slightly) and material had to be purchased by the tonne/ton or 500m +. Basically a complete roll. Even when working for a large sim company, the dollars were large.

For those currently building with Mylar, there were a few occasions when people had dropped screw drivers from the top of the screen ..... followed by a big POP and a large OH **** and then a few more OH ****'s.

The developments forward in this area is truly amazing.

Hopefully helpful:
http://www.rockwellcollins.com/~/med...a%20sheet.aspx

[Efe Cem Elci]

Especially with the vacuum considered, even a screw might have unwanted effects (read return to square one) on the "mirror".