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  1. #1
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    Collimated display build thread...

    Ok guys, I know it's been a long time without updates, so I decided to create an "official" build thread that will show our progress.

    Wayne & I have both been pretty busy with the holidays, etc. and we've not made a great deal of progress that's very photogenic.

    I finished the last sheet of parts a couple of weeks ago, so now the mirror framework is ready to be assembled.

    The parts:





    The parts marked "TOP PLATE" and "BOTTOM PLATE" are cutting jigs. In order to properly fit the "mask" that the mylar is attached to, the top & bottom of the mirror frame has to have beveled doubler plates attached. The jig was attached to my band saw and then I tilted the saw base 20 degrees and Wayne ran the parts through it.

    The doubler plates are made of 2 or 3 layers of 3/4" plywood. Here are some in the glue-up stage:



    When cut, it looks like this:



    The pic above shows the 2 layer bottom doubler. The top is made of 3 layers.

    Here's what the cut-off from one of the top doublers looks like:



    The next step will be to cut out the parts that make up the table that the mirror framework will sit on, and the base platform that the table will rest on. Some of that work should happen tomorrow (2/27/11) providing things go as planned.

    The really hard work has been done - it's all down to assembly now.

    We've also come up with a neat way of managing the shape of the mirror that allows us to continue to use a shop vac as the vacuum source. Here's a short video that describes the Arduino controlled bleed-air valve:



    The current iteration of the firmware works much better than what is shown in the video. I'm also in the process of writing a stand-alone application that will show data from the PID controller as it does it's job and will allow us to tweak the various controller parameters real-time.

    Thanks for reading folks!

    g.

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  3. #2
    150+ Forum Groupie Atomic_Sheep's Avatar
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    Re: Collimated display build thread...

    Looking really good... how many of these sensors are you using? I'm guessing just one? I suppose you would use 1 per vacuum section. Would be possible to create a more complex one with multiple vacuum cleaners and subsequently more sensors but I suppose that would probably only be necessary for really large areas. Question is... how much larger do you think the setup can get before you are no longer able to get away with just 1 suction source?

  4. #3
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    Re: Collimated display build thread...

    There's just one big chamber behind the mirror, so there's no way to individually control separate parts of the mirror. A single sensor is sufficient; we don't need to know the exact position, only whether it's too close or too far from the sensor. The firmware does the rest.

    There's a lot of leakage around the prototype frame, the final version will be much better sealed. Even so, we reached a point during testing where we were trying to eliminate as much leakage as possible, where the valve box full-open position was still too closed-down to keep the proper vacuum level. We don't anticipate any problems with the single suction source.

    The prototype is using 2 mil mylar; the final version will use 1 mil mylar, requiring half the vacuum draw. If anything, the vacuum we're using now is extreme overkill.

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    Re: Collimated display build thread...

    Overkill? Wazzat?

    g.

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    Re: Collimated display build thread...

    Excellent... thanks for that.

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    Re: Collimated display build thread...

    If anyone is curious, it takes four sheets of 3/4" plywood for the complete mirror chassis. It looks like the table may take two sheets. With any luck, we'll get some of that cut & assembled this coming Saturday.

    g.

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    Re: Collimated display build thread...

    Quote Originally Posted by geneb View Post
    If anyone is curious.......
    Anyone ? Anyone ?
    We all... sit every day for our screens, waiting for more !

    Thanks both so much for all this information.

    Hessel
    767 Level-D

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  10. #8
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    Re: Collimated display build thread...

    Thanks Hessel. I (and I'm sure Wayne does) appriciate your and the others on this forum for their enthusiasm for our project.
    The good news is that we're closer to the end than we are the beginning at this point. With any luck, much sawdust will ensue tomorrow. (FYI, a 30 gallon garbage can full of sawdust is heavier than you'd think! - I have a "turbine extractor" (fancy name for a stupidly expensive special garbage can lid) that separates the heavier chips into the garbage can, keeping them out of the DC)

    g.

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    Re: Collimated display build thread...

    I look you sistem of control mirror position, and i see oscillation in first time: forward, back, forward, back.
    How you have solved this problem?
    Or oscillations fade also position is stabilized?

  12. #10
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    Re: Collimated display build thread...

    We're using an arduino-based PID controller to control the mirror position. Our controller is not yet tuned in that video; Gene is writing an interface that will let us view the sensor readings so we can tune it better. Once everything is tuned properly, there will be much less oscillation.

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