Question about collimated display systems.

[SU-Medo]

Hessel, Thanks for the links. The last link is VERY interesting.

Matt Olieman

I was doing some mathematical calculations (Pythagoras) yestarday to design a frame suitable for my cockpit , and i discovered a big barrier , it's the "huge Space" .. but i think it would be a great way for the design if we all recognized the validity of it ..

I'm not sure if those calculations are correct or not , but they seems so logic .. correct me if I'm wrong ..

well , my Cockpit width is 165 cm ( Sorry for the non-US unit ) , so this is the idea of the calculations :-

1- Forward- Projection screen's radius
- I began by the base of the Forward-Projection screen , I planned to be as width as the cockpit .. plus say 5 cm , so the light rays would be free of hitting the cockpit , because it's the first task to guarantee that all light rays from the Forward-Projection screen would hit the whole of the mirror totally , and after i guarantee that task , i can plan the mirror radius / widths / etc according to those calculations .. See Picture below !




2 - Mirror's Radius
- After i calculated the Forward-Projection screen's radius , I then calculated the Radius of the Mirror .. The idea is the Screen would be in a distance from the Mirror less than the focal length , So i first assumed the screen would be 20 cm in front of the focal point , so the focal length would be [ screen's radius - 20 cm = 249 - 20 = 229 cm ] , Now I could calculate the Mirror's radius by multiplying the focal length by 2 [ 229 x 2 = 485 cm ] , See Picture below !



3- Mirror's Lower ( Bottom ) width
- The triangle of the lower width , it's base would be the Mirror's lower width that we aim to calculate , as we know the total sum of any triangle = 180 degrees , so as the base angle = 40* , so both the other angles = [ 180 - 40 / 2 ] = 70* .... & see the Picture below !!




4 - Mirror's Upper width
- see the picture , i guess it's now clear !!




Remarks
- The first 30* angle , to draw a latitude of 30 South ( If we looked to the screen as the earth )
- The 2nd 40* angle , because our Field of View ( FoV ) = 40* .. drawing latitude of 70 South .
- The opposite side is the same as above .
- As the half circle = 180 degrees , so the remain angle ( Mirror's Lower width's angle ) would equal [ 180 - {(30* x 2 ) + ( 40* x 2 )} ] ...

Looking forward for your thoughts

Mohammed Sayed

[SU-Medo]

I was doing some mathematical calculations (Pythagoras) yestarday to design a frame suitable for my cockpit , and i discovered a big barrier , it's the "huge Space" .. but i think it would be a great way for the design if we all recognized the validity of it ..

I'm not sure if those calculations are correct or not , but they seems so logic .. correct me if I'm wrong ..

well , my Cockpit width is 165 cm ( Sorry for the non-US unit ) , so this is the idea of the calculations :-

1- Forward- Projection screen's radius
- I began by the base of the Forward-Projection screen , I planned to be as width as the cockpit .. plus say 5 cm , so the light rays would be free of hitting the cockpit , because it's the first task to guarantee that all light rays from the Forward-Projection screen would hit the whole of the mirror totally , and after i guarantee that task , i can plan the mirror radius / widths / etc according to those calculations .. See Picture below !




2 - Mirror's Radius
- After i calculated the Forward-Projection screen's radius , I then calculated the Radius of the Mirror .. The idea is the Screen would be in a distance from the Mirror less than the focal length , So i first assumed the screen would be 20 cm in front of the focal point , so the focal length would be [ screen's radius - 20 cm = 249 - 20 = 229 cm ] , Now I could calculate the Mirror's radius by multiplying the focal length by 2 [ 229 x 2 = 485 cm ] , See Picture below !



3- Mirror's Lower ( Bottom ) width
- The triangle of the lower width , it's base would be the Mirror's lower width that we aim to calculate , as we know the total sum of any triangle = 180 degrees , so as the base angle = 40* , so both the other angles = [ 180 - 40 / 2 ] = 70* .... & see the Picture below !!




4 - Mirror's Upper width
- see the picture , i guess it's now clear !!



Remarks
- The first 30* angle , to draw a latitude of 30 South ( If we looked to the screen as the earth )
- The 2nd 40* angle , because our Field of View ( FoV ) = 40* .. drawing latitude of 70 South .
- The opposite side is the same as above .
- As the half circle = 180 degrees , so the remain angle ( Mirror's Lower width's angle ) would equal [ 180 - {(30* x 2 ) + ( 40* x 2 )} ] ...

-- Those calculations for explanation only , but of course as the upper curve’s latitude increases , the radius increases ….

Looking forward for your thoughts

Mohammed Sayed

[Snovadnb]

Hello, i read this thread all - cool! I have question:

how did you control vertical mirror radius and horizontal mirror radius ? I construct analog your system, but i can't make vertical radius equal horizontal radius =(

how did you control sphericity?

thanx!

[wledzian]

The design geometry is defined by the frame shape, which must lie entirely on the surface of the sphere. When the mylar is first installed, it will have the shape of a cone, and will deform into the spherical shape when the proper vacuum is applied. Until the vacuum is at the right level, the horizontal curvature will be larger than the vertical curvature.

How have you attached the mylar to the frame? Is it just clamped in place? If so, the extra material on the edges may stretch inward unevenly, creating an unacceptable amount of distortion.

For the prototype, we know the vacuum is correct when the mylar makes contact with the internal ribs. Once we see the distortion from the ribs (clearly visible in the photo on page 13, post#12, we reduce the vacuum just until the distortion disappears. For the full-size version, the ribs have been set back, and will not touch the mirror. Instead, we've developed an optical sensor based feedback system controlling a valve box to keep the mirror in the correct position. We'll need to install a temporary "indicator block" on one of the ribs to find the correct sensor reading when the mirror is in position, but once we've established that value, the indicator block will be removed.

[Snovadnb]

We attached mylar to the frame without adhesive tape or glue.
Only still strip.
It is no good - we understand now =)

[Snovadnb]

So well, we have two different problem: distortion and sphericity.

[wledzian]

I just found some great photos - they appear to be of the same CAE sim installation shown in the earlier video.

http://www.fotothing.com/B0B/photo/4...989d52150212c/

[vyper883]

I just found some great photos - they appear to be of the same CAE sim installation shown in the earlier video.

http://www.fotothing.com/B0B/photo/4...989d52150212c/

You know Wayne, looking at some closeups of those photos (TY BTW-great hi res pics!) I would almost swear, that the mylar absolutely gets stretched across the back surface of the frame when it's under vaccum. There doesn't appear to be much of a cavity for the mylar to to be drawn into, as opposed to your original prototype. (speaking of which I'm awaiting anxiously to see new pics your current iteration )

Seeing it up close in those hi res photos, make my brain think that it makes perfect sense for the mylar to actually be drawn onto a surface, rather it being suspended in a void. In one of the pics, I can judge no more than maybe 2 inches of the relaxed mylar from the back surface of the frame. I could be wrong, and I probably am, and I'm OKAY with that lol. But after seeing those photos, I just can't help thinking it is so. EDIT

[mikesblack]

Hi-

Thought I'd chime in here.

The mylar material needs to be optically near perfect as it is becoming a lens. Having a surface "push through" would distort the image.

Think of a mylar balloon, forgetting the wrinkles near the edges, the surface is perfectly smooth and so too is the CAE flight simulators as per these photos. The vacume pulls the mylar, or rather the pressure differential allows the mylar to " ballon" out from the rail frames that drape the material.

[wledzian]

There's not much of a cavity behind the mylar, but the mylar touches only the frame. The structure is spherical as well, probably only larger than the mirror by a couple of inches as you said. As mikesblack mentions, contact with the back surface would produce optical distortion.

The stretched mirror forms what is essentially a big drum head. With mirrors that large, the 'drum' can vibrate at a frequency which produces visible effects. One design goal is to minimize the space behind the mirror, in order to keep the resonant frequency as high as possible. With our prototype (and we hope, with the larger version as well), the mirror is too small to resonate at such low frequencies, so the large cavity is not a problem.

In other news, design work is all but finished, the frame and table parts are all cut. We need to polish some details on the screen design, but the remaining work there is little. I've got other business keeping me from the sim this weekend, but I expect we'll begin assembly on the 19th.