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Motorized masking system


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23 replies to this topic

#1 of 24 Travis Campbell

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Posted September 02 2003 - 04:35 PM

Greetings,

I've been wanting to build a motorized matting system for my 100" screen (4:3) to mask out the black bars of a widescreen presentation. However, it seems that finding the right type of materials and motors are much more an issue than originally thought.

The goal would be to rig some sort of independent curtain system that could ascend and descend from above and below the screen at the same time at different aspect ratios by remote (the remote part isn't a problem).

Has anyone successfully managed to accomplish a project like this? or am I just crazy go nuts!

I have seen screens that DaLite and Stewart offer, but the large dollar figure attached to them dissatisfies me.

Any info or alternatives would be greatly appreciated.

Thanks very much,
Travis.

#2 of 24 MikeWh

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Posted September 03 2003 - 04:43 AM

Hi, Travis. I've seen a couple examples of DIY masking, but I've only got one URL for you. I'll have to hunt around for another site that I found over a year ago-- it explains in full detail how another guy did his.

http://www.bfcc.biz/homecinemas2.html(last 2 photos in the second row of pics)

I am planning on doing similar masking, as well.... but I'm nowhere near getting the materials together. I'm thinking of using the same X-10 drapery controllers that the guy used in the link above. (http://www.smarthome.com/3142.html)
I've read differing opinions on these things though-- some people say they're rather noisy. I think a few people here on HTF use these, so maybe they can tell us what they think.

#3 of 24 Darren Hunt

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Posted September 03 2003 - 06:31 AM

Travis,

I've got plans myself of making my own masking system some time in the future for when I get a projector. My plan involves some welding and then woodwork to finish off a frame that contains the masking system and the screen together. The woodwork would be used to hit the motor and any of the other metal components used to pull the masking into place. My idea would work with vertical and horizonal masking, and if done right, could even be put together with a little more work.

Some details of what I have planned:
- A metal frame to mount all the equipment/motor to with mounting plates for the wood finishing.
- The equipment would be made up of an electric motor that is attached to two metal rods, one on either side of what you want masked. If we want to mask a 16:9 screen down to a 4:3 screen, then these two threaded bars would be mounted along the top and bottom of the screen.
- These two rods would be threaded one direction half way along the bar, and then reversed for the rest of the way.
- On each half of the bar, you will have one nut (two nuts per bar).
- These nuts would align up with the opposite rod nuts (the nuts above/below each other, NOT on the same bar) and be attached to each other via a long, vertical flat bar.
- To this flat bar you would attach your dark material and have it spooled in a spring controlled spool, one for each roll of masking material at either end of the frame.

Using an electric motor, you can slowly turn the two rods. As the rods turn, the nuts/bar will slowly move along the rod via the metal bar between them, pulling the black material out, covering the screen. By controlling how many turns the rods take, you can control how far the material is pulled out. Since each rod has half of its length threaded in opposite directions, the two bars will be brought together evenly. You could even go so far as to place optical sensors along the rods to stop the electric motor once it reaches that location(s).

When you reverse the motor, the nuts move back toward the outer edge of the screen, and the spooling function of the material is rolled back up by its springs. If you use strong enough springs, the material will be tight and very functional (I hope).

Once I get closer to purchasing a projector, I will spend more time on the details of making it.

I have the whole thing designed in my head. Maybe its over the top and way beyond what someone should do, but then, my theater room became that the minute I ripped my basement apart to create it. Why stop now!? Posted Image

Darren

#4 of 24 BenSC

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Posted September 03 2003 - 06:40 AM

Speaking of DIY solutions, what power/speed motor would be good for something like this? I've been looking at some of the motors at allcorp.com but have yet to find something that I'm sure of.
- Ben

#5 of 24 Darren Hunt

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Posted September 03 2003 - 08:26 AM

If your looking for an electric motor to operate something like I've described, I don't think it would take much to do it. All your really doing is turning two long rods which are pulling two swaths of cloth out. The forces are not that large. Its similar to a drill press with the moveable plate being controlled by the small handle. Turn it one way or the other and the platform moves up and down relatively easy when compared to how much it actually weighs and the amount of force needed to turn the handle.

I purchased an electric motor a year ago in anticipation of making this project. I can't remember what the rpm/torque the thing had. I'll have to look it up tonight. I do remember it being quite fast, so I had planned on gearing it down to a slower speed, which helps in two ways. One, the masking won't be flung across the screen very quickly with the motor running slow, and two, the torque of the output of the gearing will be greater than the motor itself, resulting in little worry if there is enough torque to properly turn the rods by the motor itself. Of course, if the motor is WAY to small to begin with, there is little chance that gearing it down for this would even work.

Darren

#6 of 24 MikeWh

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Posted September 03 2003 - 11:59 AM

Darren, I like your idea for side masking. For a 4:3-to-widescreen conversion (like Travis is interested in), I think it can be done more easily with readily available drapery equipment. But if you've got access to welding equipment, that's a great plan.

As an alternative (for 16:9->4:3 masking), I was considering just using a DC motor, a single iron pipe, 2 weighted masks, some gears, and gravity. The masks would simply wind around the pipe, one on the left side and one on the right side of the screen. Like this:
http://home.earthlin...ut/dropmask.gif

Of course, they cannot be adjusted in-and-out though. I was considering combining this mask with a top/bottom mask, so that I could get 2.35:1 masked properly, too.

#7 of 24 Darren Hunt

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Posted September 03 2003 - 04:09 PM

Mike,

Thats a great idea as well, and substantially simpler then what I have planned. With my idea, it would work really well with converting a 6:9 picture down to 2.35:1, as you mentioned, or any other ratio like than, including 4:3. Having my idea on the left and right, just to change it from a 16:9 into a 4:3 would be a bit of a waste. Your idea would be a better solution for this.

You need the adjustability in the height more than the width. The around best solution would to put the two together and have the best of both worlds.

Darren

#8 of 24 Darren Hunt

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Posted September 03 2003 - 04:16 PM

Ben,

I took a look at the motor I had bought a few years ago and here is the spec's on it:

Dayton Permanent Magnet DC Gearmotor
Model Number 4Z840
Full Load RPM: 50
Full Load Torque: 10in/lbs
Armature Volts DC: 12
Armature Full Load Amps DC: 1.6
Input Motor H.P.: 1/90
Gear Ratio: 45.4:1

If I remember correctly, I spent around $100 CAN on it.

This motor has a gear box built on it, bringing the RPM down to 50 rpm, which is slow enough for a masking system in my opinion. I believe the torque should be enough too, especially if I use ball bearing son the rods to ensure they rotate smoothly. The amount of force on the rods should be minimal and this should do the job. Have to wait until I've built the thing to see if works.

Darren

#9 of 24 BenSC

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Posted September 04 2003 - 03:03 AM

Cool, thanks for that info.
- Ben

#10 of 24 MikeWh

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Posted September 04 2003 - 12:21 PM

I found it! Here's the site I was talking about:
http://www.kathiejoh...om/masking.html

Very nice description of their DIY masking. I particularly like the tensioning system for the bottom mask. It's crude looking, but totally effective.

They used the "DrapeBoss" motor/controller, which is a little more expensive than I'd like to mess with-- about $280 (and they used 2, at that!).

#11 of 24 Travis Campbell

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Posted September 04 2003 - 01:27 PM

Thanks for the help.

I can now revisit my plans from a year ago and perhaps end up with something a little more pleasing than previous attempts. I currently utilize x10 controllers in my theater, in fact I purchased it with the intention to control the masking system, since then it now controls my lighting as well.

I like the idea of using the x10 drapery controls and the weighted/tensioning system. I will look further into these examples.

Thanks again for all your input. It is greatly appreciated.

Travis.

#12 of 24 Agnello G

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Posted September 08 2003 - 08:52 PM

Up down motorised masking only requires one motor as shown in this quick sketch. The theory is simple, when one piece masking is fully wound on the rotating pole at the top the other should be fully unwound.
As the pole rotates, the fully wound piece of masking is unwound thereby lowering it, at the same time the fully unwound pieces of masking is wound there by raising it. Piece of cake. Reverse the motion of the pole, and the top masking is wound back up as the lower masking is unwound back down.
Two Motors indeed!?! Posted Image

Here is my quick sketch: http://www.bfcc.biz/masking.jpg
I'm sure you guys can fill in the dots, hehe.

I would like it directly but it appears your moderators do not allow external linking to new members. Posted Image

#13 of 24 Travis Campbell

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Posted September 14 2003 - 07:19 AM

You've hit it bang on Agnello G. I've worked out my plans in this fashion. Just need to get the motor (x10 controllable) and the bar with mechanics.

#14 of 24 Agnello G

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Posted September 14 2003 - 09:19 PM

Glad you like it, the idea is slimplicity itself, quite often I find that people try to over complicate and over engineer the whole idea of moveable up down masking, when all thats really required is some black velvet covered balserwood, some string a pole and some staples.

#15 of 24 John Clancy

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Posted September 14 2003 - 09:39 PM

Also, if just using video projection you can get away with just having a moving top mask due to the way the zoom lenses tend to work on video projection. Just the top of the frame tends to move as it enlarges/reduces whereas the base of the picture largely stays where it is. It's only us people who predominantly project real film that really require the top and bottom masking to move in tandem as the zoom lenses uniformly increase the size of the picture all over. Also, with film you get to play with 'Scope lenses which with a 2x anamorphic print instantly gives a picture of twice the width. All jolly good fun.

As Agnello has pointed out it only requires one motor to move the top and bottom masking. Looks like some examples pointed to within this thread have used two.
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#16 of 24 BenSC

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Posted September 15 2003 - 01:22 AM

Not sure what you mean, but when masking an LCD Projector (which I would consider a type of 'video projection') for 2.85:1 material you would need top and bottom masking.
- Ben

#17 of 24 John Clancy

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Posted September 15 2003 - 01:44 AM

If the bottom of the picture is still roughly at the same height throughout the zoom range then the bottom masking does not need to move. This means only the top mask has to move up and down to incorporate all the different screen ratios.

LCD is a video projector. As is anything projecting a video image. Film projection requires top and bottom masking to move as the zoom lenses increase/decrease picture size evenly all over.

I don't think there's been anything 2.85:1 since the introduction of CinemaScope. And even then the widest ratio was 2.77:1 or more commonly 2.66:1. I think Ben Hur received a very wide treatment in some cinemas but still didn't reach 2.85:1. Since the introduction of stereo optical stripes the picture area has been reduced to 2.44:1 (2.35:1 on projection due to masking).
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#18 of 24 BenSC

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Posted September 16 2003 - 02:24 AM

Oops, your right on the ratio's, I got mixed up there. But in any event, on an LCD projector you don't zoom using the lens normally. Say your projector has an aspect of 16x9 but the movie is 2.44:1, You'll get "gray" bars on the top and bottom. Masking these with a low reflective cloth like velvet makes things look much better.

That's what I mean by needing top and bottom on video projection. I'm not sure how DLP's handle it, as I've never used one.
- Ben

#19 of 24 John Clancy

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Posted September 16 2003 - 07:29 PM

Doesn't that just mean you get a smaller picture despite the film originally being Panavision (i.e. 'Scope)? I suppose some modern multiplex cinemas do the same thing - many in the UK installed screens without adjustable side masking. However, they put in top or bottom masking to reduce the picture size on 'Scope material. Rather defeats the object of the wide anamorphic frame but more understandable with video projection.

Personally I love putting on a 'Scope print and having a picture twice the width of a flat print. Very impactive and gives the opportunity of adjusting the masking behind the curtains. Then when they open there's a lovely wide screen there.
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#20 of 24 NateF

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Posted September 19 2003 - 04:37 PM

John - if the width of your screen is fixed (which it generally is for us home viewers), and you want to use as much of the screen as possible, then if you move from 16:9 material to anamorphic, the vertical screen real estate used will diminish.

An 8 foot wide 16:9 movie will use 4.5 feet vertically. An 8 foot wide 2.44:1 movie will use 3.27 feet vertically. Assuming you don't physically move the projector, the vertical reduction will be equal on the top and bottom, resulting in a 1.635 foot gap at the top and bottom, requiring masking on both the top and bottom.

I don't know what kind of projectors they have in Great Britain, but all the ones I've seen in the US expand and contract the image around its centerpoint.

-Nate