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24fps crystal for Eclair ACL 1 motor


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#1 todd eacrett

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Posted 18 May 2007 - 03:30 PM

Thanks to one of Clive Tobin's magic boxes (speed checker) I've discovered that the crystal module on my ACL motor (single speed model), while labelled 24fps, is actually 25fps.

Anyone have an extra 24fps module sitting around? Or has anyone found a way to dig the epoxied crystal out of the cover to replace it?

Also, this ACL motor has an external brass flywheel -- something I've only seen a couple of times. I'm guessing this was an attempt to increase inertia to pull 400' mags. Would this have been a factory mod or something added later?

Thanks, Todd Eacrett
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#2 Clive Tobin

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Posted 18 May 2007 - 06:00 PM

Thanks to one of Clive Tobin's magic boxes (speed checker) I've discovered that the crystal module on my ACL motor (single speed model), while labelled 24fps, is actually 25fps. ...

I think the 25 FPS crystal is 1.000000 MHz while the 24 FPS one is 960,000 Hz if I remember correctly, both a very poor choice by modern standards. The crystal itself is likely in an HC-6 (large) case and potted in glue, wax or something.

Crystal manufacturers generally refuse to make crystals for under 1 MHz as they are large, delicate, unstable, unreliable and expensive. A technically much better approach would be to use one that is 4 8 or 10 times the frequency and digitally divide it by 4 or 8 or 10 as appropriate. 3.84 or 7.68 MHz are common microprocessor accessory frequencies and you can buy a crystal off the shelf from many distributors for well under $1. However this would require camera motor modification to feed power to the external crystal, oscillator, divider module.

If you can get a 960 kc crystal made, they will want to know the circuit parameters, that is series or ? pf parallel resonance. I can't find my drawings or I would try to figure it out for you.

Custom crystals are made by outfits such as Jan Crystal, Crystek, Northern Engineering Labs, etc. You may have to beg and plead to get them to make this too-low frequency. Yes, I know there are lower frequency crystals made such as 32.768 kc for quartz watches but these are a different cut. The space in between these frequency ranges is a no man's land.
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#3 todd eacrett

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Posted 20 May 2007 - 02:50 PM

Thanks Clive. The ACL manual says it's a 983.04 kHz crystal for 24fps (1024 for 25fps). I think the 1000/960 are pilotone freqs. It is indeed a big HC-6, encased in rock-hard glue or epoxy. I guess this is going to be more difficult than I thought.

MH Electronics say they cut crystals down to 800 kHz, so if I can find the circuit specs I'll try them. Would a custom manufacturer like that be able to test an existing crystal (e.g the 1024 kHz ones I have) to determine the parameters to make another one?

Oh, and thanks for the Maurer motor. It works great!
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#4 Clive Tobin

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Posted 21 May 2007 - 10:05 PM

... MH Electronics say they cut crystals down to 800 kHz, so if I can find the circuit specs I'll try them. Would a custom manufacturer like that be able to test an existing crystal (e.g the 1024 kHz ones I have) to determine the parameters to make another one?...

They should be able to adjust the load capacitance in their test jig until the crystal oscillates at its marked frequency. However this will incorporate any calibration error or aging drift of the sample into the new one.
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