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My daughter and I went to the movies the other day. Since we were the last to leave the theater afterward, we took a peek into the projector room and received a little tour from the owner. We also received a roll of 2:30 minute movie trailer as a gift. I thought it would be pretty cool to build a wooden machine that with the help of a flashlight and hand-crank could project this trailer onto a 5cm by 5cm screen (2"x2"). I guess I have to flash the flashlight (or whatever light source) just at the right moments and in sync with the film forward movement to create the illusion of movement. How do I do this simply? I am not looking for great quality, just something that illustrates the principle. Something mechanical rather than electronic.I remember seeing human powered apparatuses (sp?) in the "Deutsches Museum" in Munich, Germany that were VERY simple and showed a little clip. I forget how those worked though. Anyone?
The "tricky bit" is the timing wheel. It needs to engage with the sprocket holes in the film and turn on the LED briefly as each frame is centered over the LED. If you can make or obtain a metal sprocket wheel, you might simply run a sprung contact against it to make the circuit to the LED. To break the circuit, stick a piece of vinyl insulating tape on the sprocket wheel. Of course, you could use a microswitch driven by a cam or lots of other techniques, but the vinyl tape method makes it really easy to adjust the timing and "dwell angle" of the LED.
Quote from: Geezer on 14/12/2009 05:53:31The "tricky bit" is the timing wheel. It needs to engage with the sprocket holes in the film and turn on the LED briefly as each frame is centered over the LED. If you can make or obtain a metal sprocket wheel, you might simply run a sprung contact against it to make the circuit to the LED. To break the circuit, stick a piece of vinyl insulating tape on the sprocket wheel. Of course, you could use a microswitch driven by a cam or lots of other techniques, but the vinyl tape method makes it really easy to adjust the timing and "dwell angle" of the LED.An optical switch could be used to detect the black edge of a preceding frame, (or to count the sprocket holes), to synchronise the flash, (no sprocket wheels required). The flash would have to be very brief ~1/100th of a second, even then the image may be blurred by the motion of the film.In a real cine projector the film is momentarily held still when it is projected, i.e. the film does not move through the projector at a constant rate, it is jerked past the gate.
The flash would have to be very brief ~1/100th of a second, even then the image may be blurred by the motion of the film.
Just a couple of essential things (some of which have already been mentioned by others) you'll need to incorporate:1. Each frame needs to be held stationary while it's being illuminated.2. You'll need to be able to advance the film one frame at a time.3. You'll need to be be able to draw the film off the spool, and draw the film onto the take-up spool, smoothly and continuously so as not to stress the film.4. To achieve 3. you need to incorporate buffer loops either side of the gate (the place where the frame is held stationary and illuminated) so that as the film is advanced by each frame it is taken from the buffer loop and not directly from the spool. Similarly, as each frame is feed out of the gate, it runs into the take-up buffer loop.5. You'll need a shutter that is syncronised with the film movement through the gate; the shutter closes when the film moves and opens once the frame is positioned. A spinning disk with cut-outs is probably the easiest solution here as it just needs to spin at the correct constant speed.6. If you're using strong and hot illumination you'll need a blower to cool the film while it's stationary in the gate, other wise it might melt.7. If you're running a long length of film then the film and take-up spools will need to change their angular speed to insure constant linear speed. The film can be drawn off the film spool by a constant speed toothed sprocket but the take-up spool will need some sort of slipping clutch.In practice, you'll need two sets of toothed drive sprockets arranged as an inner pair, to step the film through the gate, and an outer pair to smoothly fill the feed buffer loop and empty the take-up buffer loop.
Viewing/projecting the film via a rotating mirror could cancel out the film's motion if the mirror's rotation was perfectly synchronised with the film motion, (difficult). [ Invalid Attachment ] [ Invalid Attachment ] single rotating mirror octagonal rotating mirrorhttp://web.media.mit.edu/~stefanm/TinyProjector/TinyProjector_labnotebook_prototypes.html