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Question about collimated display systems.
http://science.discovery.com/videos/...simulator.html
Found this link that has a good view of the mylar parabolic mirror.
Is it always the case that the view the crew actually sees come directly from the parabolic mirror? From this presentation, it seems that first thing that occurs is the projectors generate a 2d image on a curved ( semi spherical) screen, that I assume is at 0.5 the radius of the Mirror. The mirror then reflects this image to the crew.
Can it also be the case that the projectors beam to the parabolic mirror first and the reflected light illuminate a viewing surface that the crew would subsequently see?
Thanks.
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Re: Question about collimated display systems.
Unfortunately, the physics of optics in this case is not "reversible". The light rays relected from the mirror are collimated and the focus is at infinity. Illuminating a curved screen will result in the eyes focusing at the surface where the image appears. If that worked that would be a far less costly solution and one the sim manufacturers would have employed long ago.
JW
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Re: Question about collimated display systems.
The view seen by the crew is always a reflection of the screen in the spherical mirror. Due to the shape of the mirror and location of the image on the screen, the virtual image seen by the crew is at or near infinity.
The projectors do not beam to the mirror.
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Re: Question about collimated display systems.
Thanks castle,
Why am I to understand that it is improbable a hobbyest could build such a vacume Mylar screen successfully? The materials are seemingly not a cost barrier, and so do you know what process may be beyond reach? I have done a lengthy search and it is quite obvious not too many diy examples abound. If I didn,t know any better, I might think it could be done with favorable results, but given the evidence, or lack there of, I,m inclined not to begin and to seek some other approach. That said, I still am not at that point of totally ruling out the possibility.
Any more info related to this subject would be greatly appreciated.
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Re: Question about collimated display systems.
I'm kind of the same mind set regards a DIY collimated display. BTW the link to the short video was cool.
Part of the problem is in the precision required to shape and hold the Mylar in position, then you need to construct the curved screen on which to back project the image(s), then a projector lens to keep things in focus by accounting for the changes in the throw distance projecting a flat image onto the back of the curved screen. You might be able to use a front projection system -- easier to build a solid opaque curved surface but still need to find an appropriate lens system.
Engineering and building the curved mylar mirror is the greatest challenge. Looking at the video portion showing the mirror was informative as to the shape but very little on the vacuum system. Need to come up with some numbers to describe the mirror's geometry. Also speculating the mylar as to quite flexible to stretch in two directions so as to create a snug fit against the spherical surface. Try wrapping some mylar or any sheet of material around a sphere and you get the idea.
As shown in the video the size of the visual system also requires a little more expertise than simply throwing up a 4x8' white board
Maybe a good project to tackle in 2011....
JW
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Re: Question about collimated display systems.
Most cross-cockpit collimated displays are rear projected. Here's a link to a marketing video showing the general layout: http://www.q4services.com/images/supravue001.mov The company hosting the video, Q4 Services, provides maintenance for Mylar mirrors for just about all types of simulators.
RSI Visuals is a small company that offers a front projected collimated display. The projection path uses a spherical-section fold mirror just above the collimation mirror. http://www.redifun.com/r/products.ph...=3&category=14 Front projection has the disadvantage of requiring a second mirror, but can offer higher contrast and brighter images for the same projector light output. Rear projection has significant issues with back surface reflections.
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Re: Question about collimated display systems.
Thanks you castle and thank you Mike. Mike I appreciate the links, especially the "Supraview" movie.
I have perhaps way too many questions. I wonder if either of you or others can address the following.
If one were to start such a project, would it make most sense to first construct the visual mirror with the idea that the other components, be they front or rear projection screen projector/ first mirror, etc, being easier to make the neccessary adjustments . I assume there would be no final adjustments that could be put in place to vary the viewing mirror. So the mirror would have to be done correctly.
I have yet to experiment with N Thusim/ Sol 7, but I can only imagine an image from a parabolic mirror that is not buit with accuracy and neccesary precision could not be compensated with the pre warp process of the 2 d image this software provides.
So then the mirror.
First: Size: I can only afford a 6.5 foot radius. So would the first image need to be created on a 3.25 foot radius spherical screen? Is this even possible with Sol 7?
If this size is not a problem, what must the proper geomety for viwing mirror? I imagine a perfect sherical shape would be constant radius horizontally and vertically? I would want 220 degree viewing and I haven't considered the vertical amount yet.
Orientation of mirror to preimage. It seems there must be some way to prevent the mirror from capturing the simulator shell or any other non image related visual artifact. The examples I have seen so far are of a mirror designed to curve up and out, like a bowl. This way the orrientation is up away from the shell and only on the first projection surface.
Consistancy of mirror surface. Obviously no rinkles. This then is the role of the vacume pump. So some questions about this. Are there any other materials with good mirror surfaces that could be glued on, even painted or moulded so that the vacume pump part could be avoided? Not sure how this was done, but this is an interesting image I found. http://www.dailymail.co.uk/sciencete...ve-mirror.html
If not, how would one need to prepare the mylar sheet. Before applying to a vacume box shaped accourdingly. How would the the mylar be cut to accomidate the shape? would it be glued down? Taped? Tacked?
Thanks so much.
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Re: Question about collimated display systems.
I've been seriously researching collimated displays for inclusion in an upcoming book on simulator/computer-gaming display systems; however, I don't have all the answers yet. (I sporadically post progress reports on my website.) Here are some thoughts:
The best source of information is searching patents though Google. Patents include a section on prior art to illustrate the shortcoming the new invention is supposed to overcome. Then, of course, the patents describe the new ideas. The writing all seems to be twisted 19th century legalese. Fortunately, there are a lot of pictures. Good search terms are "infinity display", "film mirror", and "collimated display". Check out patents #3,432,219, #3,659,920, #3,785,715, #5,253,116 for starters. There are lots more.
The collimating mirror is a spherical-section of radius R. For proper focus and collimation the image must be located near or on the mirror focal surface which is a spherical-section surface of radius R/2. The mirror focal surface has the same center of curvature as the mirror. The pictures in the sales literature looks otherwise, but they really do have the same center. The odd look is because cross-cockpit collimated displays use off-axis optical paths.
R can be small or huge. Collimated systems have been built for head mounted displays and for wide-body aircraft simulators. You can scale it to meet your needs.
The field of view details can be worked out with ray tracing and high school trig and geometry. Ray tracing with a CAD drawing system works well. I've been using TurboCAD. DoubleCAD XT would probably work and it's free.
Metalized Mylar can be used to make film collimating mirrors. Up to about 40 degrees of vertical field of view, building one is merely difficult. Building one with a 60 degree vertical field of view apparently requires magic. SEOS figured it out a few years ago. Rockwell Collins was so impressed they acquired SEOS in 2008.
I agree. Start with the mirror. If the mirror doesn't work out, nothing else matters.
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Re: Question about collimated display systems.
Some other technique other than a vacuum system to hold the mylar will not work. I tired glue with very poor results.
Built a small frame, 5' radius, 60hx45v degrees FOV, just no way to get a smooth application of glue and no matter how thin I spread the glue, the mylar always had bumps and irregularities, and it was impossible to "stretch" the mylar to make it conform to the surface.
So you need to devise a manufacturing process to precisely create a concave surface that is very smooth and uniform. I imagine you could tolerate some variation in precision but it would not be much. And don't forget the projection screen has to be quite precise as well.
Another problem to solve would be some non-uniformity of the mylar attach points along the edges which will result in variations in the tension applied to the mylar. This would be a problem if the mylar was "free standing" and relying on the vacuum to control the shape. If you suck the mylar onto a solid surface, imagine that should not be a problem.
I don't have the links handy but the technique of deforming mylar and glass mirrors with a vacuum has been used by astronomers to produce optical collection mirrors starting in the '80s. The mirrors were much smaller and they actually used the vacuum as a control function to achieve dynamic focusing of the mirror.
My approach would be to pick some arbitrary size as noted above, maybe even smaller, and focus on the mechanical and manufacturing details. That is one question I'm still puzzling over --- does the vacuum actually shape the mylar attached to a frame or simply suck it onto a surface that defines the shape?
One other consideration I've not researched yet is the lens requirements and what f-stop is required to project the image onto a curved screen that is "nearly" in focus everywhere or some other lens arrangement to handle the problem.
JW
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Re: Question about collimated display systems.
I just bought a roll, so can't wait to experiment.
My thoughts are to use phenolic or other soft flex material cut into long narrow strips that would act to clamp down on the Mylar film. The strips would be set front and back along the edge of the Mylar sheet. I would need to figure out the interval for spacing drill holes. The idea is to not only hold the Mylar in place, but also to prevent wrinkling at the edges, so there would need to be a tight enough, but also fairly uniform holding pressure all along.
These strips would fit into a track that would be set in the semi sphere frame along the mirrors border. I imagine this track would be made of the same material. The track would need to be snug, but also air tight for suction. I imagine perhaps using a router so that a grove can accommodate the phenolic track housing . The track groove would need to be set square and consistent along a precise arc.
The material should slide into place. I would also need to have these strips set along the vertical edge. Perhaps the track groove would be set so that the track would lie into the frame, set back down.
I need to figure out how much play there is in the Mylar and how and how cut and bunch the material prior to affixing the track. From the movie link that I provided, seems the Mylar prior to suction shows wrinkles at 45 degrees to vertical. Sort of reminds me of those old instant popcorn tin tops that were twisted or rotated so that when the tin expanded with the popping it would expand and rotate out. This is an exaggeration as the wrinkles on the mirror are very slight, but perhaps telling none the less.
Lots of unknowns, so I too will start with smaller models, e.g. 1-2 foot radius. Perhaps in time we'll get it figured out. I know that it would be a terrific enhancement. We shall see what challenges lie ahead. I'll keep you all posted as I progress, or not.
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Re: Question about collimated display systems.
I've been thinking about this nasty problem for the last three weeks. So much so that I didn't do a thing with it today - I gave my poor IBM 5160 some quality time instead. *laughs*
First, you need one of these...
http://www.diy-cockpits.org/coll/ima...rror_frame.jpg
...but that's not all. :)
I'm going to try to get a frame that will fit into the one shown above to retain a solid skin - hopefully I'll get to it tomorrow.
One thing I noticed about the video from How It's Made - the mylar _crawls_. I've only seen that when a material is being drawn against a solid surface. I strongly suspect there's either a solid skin with a Metric Buttload(tm) of tiny holes, or there's a gas permeable solid like MDF there. Fortunately, I've got me a little gadget that's perfect for drilling holes in Metric Buttload quantities. :D
I should note that the frame in the picture above is a 60 degree wide slice of a 48" radius circle. It's 40 degrees high. The top is at zero degrees. This is a good size for a practical test. It also means that if it works, I only have to build two more to get 180 degrees. :)
g.
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Re: Question about collimated display systems.
That is one fine pic of one fine piece of work and craftmanship. Yes, drawing the mylar against a solid surface is the way to go. Would be most interested on how you construct the surface and the tolerances you are working with. I guessing that is plywood or some other type of non permeable material.
Hers is a suggestion on "attaching" the mylar.
Rather than trying to pre-measure the material and attaching it, first construct your frame and surface and the vacuum system. get some sort of "referee" material, cut it into sections, turn on the vacuum, and slap the strips in place. Cut an oversized piece of mylar that you know will extend beyond the edges of the frame. Roughly position the mylar against the "referee" material. Once the mylar is sort of in position, remove a section of the "referee" material by sliding it out from under the mylar. Hopefully, the mylar will be drawn against the surface. Continue until all the strips are removed.
If that works and the mylar is in position, simply mark the attach points on the mylar or maintain the vacuum and secure the mylar to the frame, shut down the vacuum and trim as required.
Warning, I've NOT tried this myself. Just a crazy idea.
JW
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Re: Question about collimated display systems.
Great work! Curious about R. I was considering 6 feet and 30 degrees vertical but if there isn,t a disadvantage going to 5 or less feet, it would make for moe space in an already crammed room. Do you have any ideas on this?
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Re: Question about collimated display systems.
Thanks castle
Can you explain "referee material"? Not quite sure I understand exactly what you have in mind.
Thanks.
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Re: Question about collimated display systems.
Quote:
Originally Posted by
mikesblack
Great work! Curious about R. I was considering 6 feet and 30 degrees vertical but if there isn,t a disadvantage going to 5 or less feet, it would make for moe space in an already crammed room. Do you have any ideas on this?
Mikesblack, you realize a 6 foot radius will give you an edge-to-edge width of 12 feet, right? The radius of the screen is going to be dictated by the size of the simulator cab. I picked 48" because I can use it with a couple of different cockpits - IF it works. Making even a "good enough" thin film mirror is a brass plated nightmare. :)
BTW - wledzian, I've got the projectors set up and running, so if you want to stop by and see it in action, let me know. I'm going to be taking it down at some point in order to move it, so let me know as soon as you can. :)
Here's what my next step looks like:
http://www.diy-cockpits.org/coll/ima...ame_insert.jpg
The gray colored components need to be cut out, but with any luck I'll be able to do that tomorrow.
g.
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Re: Question about collimated display systems.
Referee material --- anything that would block the holes and create a suction and substitute for the mylar. wrapping paper, aluminum foil, 8x11 paper sheets, etc.
Would also be a way to test your vacuum system and seals by blocking air flow through the pin holes and use smoke to see if air is being sucked in from other spots on the frame or joints.
JW
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Re: Question about collimated display systems.
"Reference" material maybe? :)
g.
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Re: Question about collimated display systems.
Thanks for explaining. I understand what you mean. Makes good sense.
On a separate note, I would love to find some plans or blueprints of these level D C. display systems. That would take out much of the guesswork.
I wonder how helpful the manufacturers would be if someone called over to explain that he or she was a hobbyist, looking for some helpful ideas or information. I wonder if the response would be guarded. Perhaps a manufacturer would be resistant to help someone if they thought by sharing could compromise their competitive advantage.
I have found Mike P. work and links to be a great help, so thank you Mike. I look forward to your new book. I have been reading your second book of late. Very interesting indeed. I'm sure I'll continue to check out your site for updates on this.
I will be happy to share what I find as I gather more information and look forward to exchanging ideas on this. Given that this seems like uncharted waters for the general DIY guy or gal, makes it even more intriguing.
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Re: Question about collimated display systems.
geneb,
My pit is 11.5 ft across at the floor and at the back. I have roughly 2 ft from side of pit to my wall, perhaps a little less on the other side. I am considering that my radius origin is located at the throttles in the center of the cockpit. The widest part of the circle and where I am measuring R is at the top of the Mylar screen, where the angle relative to the floor is 90 degrees.
I'm considering the following.
Angle of arc from bottom to top of screen. Whatever I can do in order to keep the Mylar material wrinkle free. Width based on the arc based on 30 degrees and r= 6 feet is approx. 3 feet assuming my math is correct. ( 2Pi R) = approx. 36 ft diameter. So At 10 degrees of arc( 36/36) = 1 foot. I need to be sure that when I look out of the cockpit window I have enough viewing surface above and below cockpit window so there isn't an interruption to the image. If I bring these elements into consideration perhaps I might get away with 3 feet viewing surface. I need to experiment with curves of various radii and arc to see what will work.
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Re: Question about collimated display systems.
Just in case you've not found this site and want more info on concave mirrors and optics..
http://www.physicsclassroom.com/class/refln/u13l3d.cfm
Your instincts are probably correct, no manufacturer is going to supply details, trade secrets, and proprietary data to a voice on the phone no matter how sincere, honest, and trustworthy the caller may be. Afraid we're on our own here. OTOH there are some very bright, intelligent, and creative folks in the hobby side of simming as well as those on these forums.
Plus we're not going for FAA Level D certification. Close enough works for me ;-)
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Re: Question about collimated display systems.
Quote:
Originally Posted by
castle
Just in case you've not found this site and want more info on concave mirrors and optics..
http://www.physicsclassroom.com/class/refln/u13l3d.cfm
Your instincts are probably correct, no manufacturer is going to supply details, trade secrets, and proprietary data to a voice on the phone no matter how sincere, honest, and trustworthy the caller may be. Afraid we're on our own here. OTOH there are some very bright, intelligent, and creative folks in the hobby side of simming as well as those on these forums.
Plus we're not going for FAA Level D certification. Close enough works for me ;-)
Good link JW. There lies the problem, the technological, know how and the resources for R&D. We can have all the information regarding how it's done, but when it comes down to the bottom line....... it's nearly impossible for one person to take on this task and I'm just talking about the mylar mirror. The overhead rear projection screen is in itself a major or almost impossible undertaking, if you really think about it. Between the two of them, there is no room for imperfection.
I've researched this for over 15 years, I've tried all sorts of mirror setups, I've studied actual mirrors on a level D sim. I've got rolls of Mylar, different thicknesses and qualities. Even to stretch mylar on a flat surface is a feat itself. Try to find an imperfect piece of mylar.... wow, the frustrations.
If some one can find a way of making this happen, this person will be THE hero of our hobby. :)
Matt Olieman
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Re: Question about collimated display systems.
There were a series of reports funded by government money all with the appealing title, "Wide Angle Multiviewer Infinity Display Design". So far I've run across abstracts for 3 different reports with this name. They appear to be have been distributed in micro fiche format to a few university libraries. None of the libraries will send micro fiche out as an inter-library loan. It is possible to buy hard copies from the NTIS for $48 to $60 each. Not being able to preview them, I'm reluctant to spend the money, especially because there is no guarantee that the print-on-demand from old micro fiche will be of readable quality. There is also the issue of just exactly what the reports contain. The abstracts sound appealing, but there is no indication of the level of detail or its usefulness.
I've considered driving to UC Davis California to visit the library as the catalog says they have two of the reports, but I haven't gotten there yet.
If any of you gentlemen are located near a good university engineering library, you might check to see if these reports are available there. They might be full of gold plated hand waving, or they might be real gold mines for this project.
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Re: Question about collimated display systems.
Hi Mike,
Were Rhinehart and Shaffer some of the authors of these reports? Any more info such as fiche numbers.
JW
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Re: Question about collimated display systems.
Quote:
Originally Posted by
castle
Hi Mike,
Were Rhinehart and Shaffer some of the authors of these reports? Any more info such as fiche numbers.
JW
Here's what I've got so far:
Wide-Angle, Multiviewer Infinity Display Design by L.W. Shaffer, J.A. Waldelich; Air Force Human Resources Laboratory, Advanced Systems Division, [1977] NTIS product code# ADA053679, Library call: DOC D 301.45/27:77-67 mf11 [@ UCDavis Shields Library]
Wide-Angle, Multiviewer Infinity Display Design by Robert M Rhinehart; Air Force Human Resources Laboratory, Advanced Systems Division, [1977] NTIS product code# ADA051158, Library call: DOC D 301.45/27:77-71 mf11 [@ UCDavis Shields Library]
Wide-Angle, Multiviewer Infinity Display Design by Ian Whyte, A.W. Zepf; Brooks Sir Force Base, TX. : Air Force Human Resources Laboratory, Air Force System Command, [1982] NTIS product code# ADA116308 , Library call: D301.45/27:81-27/V.1-2 [@ New Mexico State Library] Series: AFHRL-TR ; 81-27 (I-II)
NTIS is the US Department of Commerce National Technical Information Service www.ntis.gov
Doing a Google search on the title turns up various links, but no real content. There's even an entry in Google book scan, but no preview.
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Re: Question about collimated display systems.
I found these abstracts listed in the bibliography of the AF Human Resources Lab. http://www.icodap.org/papers/AFHRL/index.html
Whyte, I., & Zepf, A.W. Wide-angle, multiviewer , infinity display system. AFHRL-TR-81-27(I), ADA116 308. Williams AFB, AZ: Operations Training Division, June 1982. Project ILIR, Contract F3361S-79-C-0002, American Airlines. NTIS. This study examined the design specification for a wide angle infinity display system with minimal distortion, convergence, dipvergence, and collimation errors for use on wide-body-aircraft simulators. The report includes a recommended final design specification; a survey of potential fabrication technologies for projector, screen and large mirrors; an approach to fabrication of a large display system; and finally, assembly and alignment techniques of mirror segments for a large display. (Note: Dipvergence refers to vertical movement of eyes up and down as opposed to side to side. (94 pages)
Shaffer, L.W ., & Waidelich, J.A. Wide-angle, multiviewer infinity display design . AFHRL,-TR-77-67, AD-A051 158 . Wright-[Patterson AFB, OH : Advanced Systems Division, September 1977 .Project 6114, Contract F33615-76-C-0064, General Electric Company. NTIS. There has long been aneed in aircraft simulation for a wide angle visual display that will accommodate the entire crew of a large aircraft type such as a bomber or tanker. This study is concerned with the approach and design of a wide angle display for multiple crew members in large aircraft simulators . The study traces the development of a concept from existing simulation methods. Throughout its 180° by GO° field of view which accommodates pilot, copilot, and instructor pilot the final design meets most of the requirements of the original specification . Because of its relatively large optical components the fabrication of the display will be of a developmental nature itself . (116 pp.)
Rhinehart, R.M. Wide-angle, maaltiviewer infinity display design . AFHRL-TR-77-71, AD-A053 679. Wright-Patterson AFB, OH: Advanced Systems Division, December 1977 . Project 6114, Contract F33615-76-G0052, McDonnell Douglas Electronics Company. NTIS. A research design study was undertaken to define an extended field of view (60° x 180°) infinity image display, suitable for multiviewer use on wide-bodied aircraft simulators. Mosaicking of single channel units, both reflective and refractive was investigated, along with extended field, off'-axis reflective systems. Major emphasis was placed on the investigation of extended field of view, off-axis reflective systems. Various figured screen and mirror combinations, ranging from spherical to high order aspherics, were designed and evaluated. Two specific designs were selected, optimized and evaluated over an extended viewing volume. (78 pp.)
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Re: Question about collimated display systems.
I found the Whyte & Zepf report for sale in pdf from NTIS. I bought and downloaded it. It is interesting in, shall we say, a historical way. It does not mention film mirrors at all. The optical design reflects very early approaches to the cross-cockpit design goal.
My thought is that information in recent patents is both more detailed and more useful.
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Re: Question about collimated display systems.
Thanks, Mike
I would put my money on the 1982 study. If the abstract is accurate, the phrase "approach to fabrication" might provide some insight. While they all are a bit dated. might still be a good starting point.
You can download an electronic copy of the 1982 Project ILIR study for $15 from NTIS. Catch is that file is reproduced from "best digital master available", that could mean an optical scan of an old micro-fiche. Think I'll give then call tomorrow....
JW
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Re: Question about collimated display systems.
He, he, guess I won't call them.
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Re: Question about collimated display systems.
Mike,
Thank you very much for all of this as well as your insights.
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Re: Question about collimated display systems.
Matt,
Can you say from your experiences what the most demanding element you found was? Sounds like there are a bunch, but at any point did you think there was possibility you might have been close to getting it.
It sounds like you have encountered too many obstacles to feel satisfied continuing or that it may be a further exercise in futility to care to bother with it all. After all, this is supposed to be fun.
That said, I should think that your many years of exhaustive and frustrating experience trying to build this has led to many valuable insights that could be of tremendous value. I wonder if you think that a collaborative undertaking by this community and most especially with your rich experiences could be what it takes to make this at all plausible.
At the end of the day, the technology is there and it is a physically reality practically speaking. I would be most grateful for your insight and experience, so long as you come to find it worth your time to do so. With that and the input of diversity of this interested crowd, who knows, perhaps we'll get there.
Thanks,
Mike
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Re: Question about collimated display systems.
Mike (mikesblack), the first question that comes to mind, are we capable to form a cast for the mylar mirror? The answer is yes. Secondly can we vacuum form the mylar to the cast? The answer again is yes. So than where lies the problem, it's the imperfections in the mirror or the mold. First the mold has to be perfectly curved to act as lens and align with the curvature of the rear projection screen. Secondly foremost difficult part is the imperfections in the curve, a slightly flattened portion of the mold (mirror) and the whole mirror is out of whack.
Obviously, the mold can not be hand made, there is a tremendous amount of precision involved to make this work, that's the major short fall of a self made collimating mirror.
There is a video floating somewhere, at I saw within the past several years, where they showed to vacuum fit of the mylar to the form (mold). I was surprised how quickly it took place. The tiny holes in the mold has to be 10's of thousands and very small as not to have the slightest imperfection. The mylar is actually glued to the mold.
The development cost of a collimating mirror would be tremendous compared to buying a ready made mirror and screen. Then comes the high resolution projectors and then the special lenses, where talking about thousands of dollars for a single lens.
Mike Powell has presented amazing technical information regarding design of the collimating mirror for a cockpit, it certainly gives you a jump start. Even if you had the exact specifications, the above mentioned obstacles would still be there.
I'm not saying it can't be done, it's a matter of how much money you want to spend. I hope someone does come up with a solution to make an affordable design for a cockpit collimating mirror.
I hope I made some sense out of what I wrote, sometimes a just babble...... :) :) :)
Matt Olieman
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Re: Question about collimated display systems.
Matt,
Not at all. I appreciate your reply and If you don't mind, I have a few questions for you.
You mentioned many things. I'd love to find this video and if you know or find a link, I would be most grateful.
You mentioned here and I believe in another post on this topic that the Mylar is glued to the mold. Are you saying that the suction acts as a one-time process for which it enables the Mylar to be spread uniformly and finally joined permanently by glue? I was thinking that the vacuum was actually part of the set up that was used to keep the Mylar held to the mold and used continuously.
Also, do you have any idea what sort of result one would find using conventional projectors, assuming a good mirror, projection screen set up?
I have no idea the scope and scale of this project, so forgive my naiveté or simplistic thinking. If nothing else, I am always happy to learn new things.
Mike
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Re: Question about collimated display systems.
If you wanted to go for a simpler solution, it might be within a hobbyist's power to create a WAC (Wide-Angle Collimated) window display unit. Older sims used them, before large mirrors were practical, and plenty of sims still have them in today. You can still buy them new, too. Basically they use the same parabolic mirror as the cross-cockpit display but the mirror is sized for the window it's put in front of - the radius of the mirror being just a little larger than the width of the window. Put a half-silvered mirror directly in front of you at 45 degrees, then up top, put a CRT (I suppose you could use a very bright TFT) looking directly down onto the half-silvered mirror. The picture on the monitor is reflected onto the spherical mirror and then back at you, duly collimated. Get the focal length right, position the mirror and yourself in the right place, and bingo.
There are surprisingly few actual pictures of this in the internet, which is annoying... Matt Ford has a good section on his site about his Level D display system salvaged from an old Boeing sim which uses WACs:
http://web.me.com/mattford1/Site/Lev...al_System.html
The key is the mirror. You can get concave spherical acrylic mirrors from science and educational supply outfits, these are sometimes used by people creating solar stoves. I found one with a diameter of 600mm - can't find the link now, unfortunately - and it's possible they may go bigger. At 800mm - 1000mm they'd become useful for front-view windows on a smaller cockpit. Many are not a single mirror surface but made from strips of reflective material with joins, which is OK for a solar stove but not for sim use.
For a fighter pit or any kind of pit with small windows - maybe a GA pit? - this might be a goer. I doubt you'd be able to buy mirrors big enough for a heavy jet simpit without going to custom fabrication. You'd also have a lot of unneeded top and bottom to the mirror which you couldn't just cut off because the mirror would then deform. Probably have to cover the unused bits in black.
It's interesting that it seems very easy to get hold of reasonably large convex spherical mirrors - lots of companies sell big ones you put up in a corner of a warehouse so you can see all around you - but concave mirrors, not so much. Plus of course not just any old concave mirror will do.
I suppose at smaller sizes - up to a meter in diameter - you might get your local friendly plastics company to make you a few as a job lot.
But I think the full-on precision machined mirror you need for a cross-cockpit display is just beyond the capabilities of anyone without a proper manufacturing plant at his or her disposal. I suppose Matt Sheils might be able to manage it :)
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Re: Question about collimated display systems.
I went back to take another look at the "how it's made" video. Somethings to note.
The shape of the mirror section seems to indicate that the top edge starts at a latitude below the equator and and looks to be much closer to the "south pole" wherein the lower circumfernece or line of latitude has a much smaller radius than the upper latitude. Eyeballing it might be something like lat 20 degrees south to say around 50 degrees south.
The vertical curve along the top edge appears to have a rather large radius and is greater than the lower radius. If the person in the scene is 6 feet tall, my guess is that the radius of the sphere from which the mirror section is mapped is close to 15feet or more. Keep in mind the radius of the Artic Circle is much less than the radius of the Equator. Tough to tell as there is probably some distortion with the camera and depth of the image due to the lens. Note how the yellow beams of the holding frame are curved. I'll bet lunch that those beams are, in fact, straight.
The other item to note is the closeness of the projection screen to the mirror as it is visible when the scene shows the mirror moving into position.. Clearly, the projection screen is inside the focus of the mirror which produces the larger virtual image for the OTW. Also the view from inside the cockpit shows the mirror with wrinkles, so that would argue for an active vacuum system. Or did Matt really mean to say "glue" as in the sticky stuff.
Mike, you might want to rethink your calculations as to size, location, and perspective. The projection screen clearly overhangs the cockpit shell and can only be a few feet from the mirror.
Matt is right, It is a tough problem but I always like a challenge :-)
JW
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Re: Question about collimated display systems.
Concave spherical mirror. Thanks Neilh, I couldn't think of that term. :)
JW I'm with you, it's a tough problem and a fantastic challenge...... anybody..... GO FOR IT!!!! :)
Mike (mikesblack), The video..... :) I'll do my best to find it. Regarding the Mylar being glued. The vacuum holds it in place for several hours as the glue cures (yes, the sticky stuff :) ). They did not mention what the glue was, but I amagine something that would not cause imperfections.
Regarding the individual Concave spherical mirror, yes, Matt Ford uses it on his cockpit, you can find pics of it in the "March 2010" Builder of the month. Go HERE. Project Magenta's Flight sims use the individual concave spherical mirrors, matter of fact at one time they were selling them for around $4K each (NEW). I considered it. If you ever flew a sim with these type of mirrors it would not take long to be a bit frustrated, particularly if you want to be wrapped with scenery. If you're in the CPT seat, you can't see out of the F/O window, all though you can see out of the side windows. If you were able to see the F/O window, you would see the identical image as the CPT side (they are the same).
There is a GA Sim, I think a C172 that uses the individual Concave spherical mirror. I believe there are some posts here and pics of the sims progress, it was a school project in Europe (I think).
Regarding how close the mirror is to the overhead screen. The first time I walked between the cockpit and the mirror, I was amazed how close they were. First of all, from inside the cockpit, it gives you the impression the mirror has quite a bit of distance.... what an illusion!!! :) I was constantly reminded.... "DON'T TOUCH THE MIRROR!!!!" :)
This is an amazing topic and a fantastic challenge, I know...... I believe in our hobby we've conquered every aspect of building a Flight Sim Cockpit, except the concave spherical mirror, 150 to 180 degrees.
There was a time where builders believed, motion for the sim was not practical to make and was way beyond our budget. Someone in New Zeeland came up with an idea using Automobile axels, starter motors and other parts and made a full motion sim for around $3,000. We've developed further than that, and all sorts of contraptions are available in affordable form.
Our hobby still is not a cheap hobby, but compared to 8 to 9 years ago, you can build a sim for much less, AND it's plug and play. :) :) :) Oh well..... I can go on and on.... LOL.
I see hope for the 150 to 180 degree collimating mirror for the home build cockpit....
Matt Olieman
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Re: Question about collimated display systems.
Quote:
Originally Posted by
mikesblack
geneb,
My pit is 11.5 ft across at the floor and at the back. I have roughly 2 ft from side of pit to my wall, perhaps a little less on the other side. I am considering that my radius origin is located at the throttles in the center of the cockpit. The widest part of the circle and where I am measuring R is at the top of the Mylar screen, where the angle relative to the floor is 90 degrees.
That makes sense. I just wanted to make sure you were aware of the size requirements. :D
Quote:
Originally Posted by
mikesblack
I'm considering the following.
Angle of arc from bottom to top of screen. Whatever I can do in order to keep the Mylar material wrinkle free. Width based on the arc based on 30 degrees and r= 6 feet is approx. 3 feet assuming my math is correct. ( 2Pi R) = approx. 36 ft diameter. So At 10 degrees of arc( 36/36) = 1 foot. I need to be sure that when I look out of the cockpit window I have enough viewing surface above and below cockpit window so there isn't an interruption to the image. If I bring these elements into consideration perhaps I might get away with 3 feet viewing surface. I need to experiment with curves of various radii and arc to see what will work.
Keep the mirror as close to the cab as you can without it shadowing the image and you'll be fine. There will be some experimenting for sure though. :)
g.
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Re: Question about collimated display systems.
Mike,
I came up with slightly higher numbers..
If you want a mirror that subtends 45 degrees of arc which seems to be the standard size, ( don't think 30 degrees will provide a sufficient FOV) for mirror with 6' radius
(45.0/57.2957) * 6.0 = 4.712 feet
you might be able to get by with a 5' radius mirror in which case you will need
(45.0/57.2957) * 5.0 = 3.92 feet
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Re: Question about collimated display systems.
I wonder what the effect would be if you took an acrylic mirror sheet and bent it into a parabolic curve just in one direction - horizontally - and then put a similarly-curved and appropriately scaled rear-projection screen at the focal point and projected onto that screen? Would you get partial collimation? What would that look like? I don't know enough optics to really think it through. I'm sure the reflected image would be distorted vertically at the corners, but if you removed that distortion using NTHUSIM what would the end result look like? Would your eye see it at a near focus or infinity or some kind of half-way house? Precisely bending acrylic mirror sheet into a simple curve is well within the capabilities of many people here.
Also - acrylic mirror sheet is basically clear acrylic with mylar on top / underneath. If the curve was gentle enough - say, using a large parabolic satellite dish, if you could get hold of one, as a mould - and you heated the acrylic up enough to be formable, would the mylar cope with the scretching and deforming without cracking or seaming? Could you even get the mylar film up to that temperature without it burning off? Anyone tried that?
I suppose you could maybe make several sectional moulds of an overall mirror shape using heavy-duty polystyrene blocks which are easy to carve and adjust, form acrylic to each one using the heat-it-in-the-oven technique, then look at mylar-covering each segment individually. That'd surely be easier to do? Yes, you'd get a less perfect display, but it'd be better than nothing by a long way.
Just throwing out ideas here...
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Re: Question about collimated display systems.
I like those ideas neilh. I too wonder about the horizontal curve only. At least in terms of simulating paralax and proper runway allignment per Cpt or FO seat. This is something I will experiment with when I start to work with the mylar.
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Re: Question about collimated display systems.
Hi all,
I like the idea of the one dimentional curved mirror(cheap) and the problem I see is that it can not be mounted vertical, as in 90 degrees to your eyes. Because the "screen" must be over your head, you need to tip the mirror back at an angle to see the screen that is above and behind you. This will give your horizon a curve that can be at the right elevation directly ahead but will turn up at the outer edges like a smilley face. So my question for the day is would this "Immersive Display Lite" program that is on the main page be able to un smile the horizon and bend it back so it looks flat? It is only 40 bucks so I think I will buy it and take the mirror off by bathroom door and do some expirimenting. I already have a projector mounted to the cieling in the center of the room and a small mirror on the wall above the overhead so all I need to do is put a piece of white paper over the existing mirror and re focus the image on the paper then mount the large mirror in front of the sim.
Now that I am imagining this what about a curved screen, the one behind you, also bieng tipped at an angle might be able to curve the horizon the other way cancelling out the curved horizon on the big mirror?
My bathroom mirror is only about 18" wide by about 5 feet tall and is glass so I can't bend it much, but enough to test the concept. I will report my results tomorrow.
Andy Smith