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Crystal Sync Motor Schematics


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#1 Bryan Darling

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Posted 12 May 2006 - 02:43 AM

I'm doing some research on crystal sync motors and was hoping someone might have information and schematics. Anything would be helpful. I'm studying how they work from a component/electrical perspective. I'm fairly new to electronics so any techinical and schematic information would be really helpful.

Thanks so much.
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#2 beanpat

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Posted 13 May 2006 - 02:30 AM

I'm doing some research on crystal sync motors and was hoping someone might have information and schematics. Anything would be helpful. I'm studying how they work from a component/electrical perspective. I'm fairly new to electronics so any techinical and schematic information would be really helpful.

Thanks so much.


Hi,
I'm an electronics hobbyist myself. I too have pondered the same project for my arri-s. if you do a web search for motor controller chips you'll find that the manufacturer will have example schematics or test circuits for their chips and provides at least a good starting point. also check out the new brushless motors used in R/C planes and cars at a hobby store. you can get a really nice ball bearing brushless motor and 3 phase controller for $60 or so. they seem like an excellent candidate to run a camera. they are also much more quiet than brush motors. the cool thing about the brushless 3 phase motors is that you do not need a feedback signal from the motor. the speed can be precisely controlled just by the frequency of the ac going to the motor.
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#3 Bryan Darling

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Posted 13 May 2006 - 02:51 PM

Thanks,

I had been looking into the brushless DC motors and those piqued my interest. The thing I'm still trying to get around in my head is speed control of the camera, in achieving the proper frame rate and it maintaining. I was looking into feedback circuits. However still doesn't answer how I'll know that it's turning the camera at the proper frame rate.
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#4 Nick Mulder

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Posted 13 May 2006 - 07:36 PM

Thanks,

I had been looking into the brushless DC motors and those piqued my interest. The thing I'm still trying to get around in my head is speed control of the camera, in achieving the proper frame rate and it maintaining. I was looking into feedback circuits. However still doesn't answer how I'll know that it's turning the camera at the proper frame rate.


have a read here:

http://en.wikipedia..../PID_controller

you have your crystal oscillating at a known frequency which is a multiple of your desired frame rate (which is usually a much higher frequency crystal whose oscillations have been divided down) - then you also have a sensor connected to your motor reading its rpm that provides another frequency, this is achieved with an encoder (the frequency is usually a multiple of the rpm, encoders usually have from 50 to up to 2000 ppm 'divisions per revolution' if you like) ...


to make things simple, imagine your encoder gave one pulse per revolution, so if you were shooting at 25fps you should get a 25Hz pulse, your crystal will always give a 25Hz pulse, but if you were to give voltage to your motor and it went say 23fps (ie 23Hz) there would be an error of '2' - you give more voltage in proportion to this error, which will make you get closer and closer to your desired frame rate - a crystal sync device provides the crystal frequencies, the comparative circuitry that works out the error and acts upon it is usually in the camera ...

There is so much to type.. but that wiki is a good place to start leaning about PID loops (the P stand for proportional)
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#5 Nick Mulder

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Posted 14 May 2006 - 12:26 AM

... from 50 to up to 2000 ppm 'divisions per revolution' if you like) ...


think I was a bit tired when I wrote that, should be ppr, not ppm which is a chemistry term :lol:
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#6 Bryan Darling

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Posted 14 May 2006 - 02:52 AM

Thanks so much for that. It's a tremendous help and makes a lot of sense. I printed out the Wiki entry and will read it tomorrow. To clarify something, I take it the 25fps/25hz assumes a 1:1 shaft. Now the bolex I have has an 8:1 shaft so I would assume you'd divide 24 by 8 to get the frequency needed. This is based on my thought that 1:1 vs. 8:1 is applicable to frames. For example, the 1:1 means that one revolution equals one frame and the 8:1 means one revolution equals 8 frames.

Do you agree?
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#7 Nick Mulder

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Posted 14 May 2006 - 04:03 AM

Thanks so much for that. It's a tremendous help and makes a lot of sense. I printed out the Wiki entry and will read it tomorrow. To clarify something, I take it the 25fps/25hz assumes a 1:1 shaft. Now the bolex I have has an 8:1 shaft so I would assume you'd divide 24 by 8 to get the frequency needed. This is based on my thought that 1:1 vs. 8:1 is applicable to frames. For example, the 1:1 means that one revolution equals one frame and the 8:1 means one revolution equals 8 frames.

Do you agree?


24/8 yep you got it... that is if you were to have only one sensor and one sensing element per revolution.. there is nothing to stop you from putting as many as you require to get the best resolution... the more sensors the more accurate your eventual drive would be ... having a 1ppr sensor on your 8:1 shaft aint going to help you very much for this application...

instead you could spin an LED around on the 8:1 shaft and have 8 equally spaced phototransistors reading it, or an even better idea you could have one LED and one phototransistor reading a spinning disk mounted on the 8:1 shaft, put black and clear stripes radiating from the centre that will alternatively hinder and then let pass the light from the LED - this is exactly what happens in encoders you can buy of the shelf...

there is nothing to stop you from using a 2000 ppr encoder checked against a 6.25 KHz crystal. I suspect altho I am yet to open it up and confirm that my EL has a 40 ppr encoder 1:1 - it could be some multiple or division of that tho...

I should say that I'm still only at/around your level also, just getting to grips with the concepts and am yet to fully understand the implementation in terms of code for microchips and/or discrete logic (CMOS stuff), let alone analog PID control - But soon I hope to upgrade my Bolex EL to automatically go to xtal sync when I switch to 24 or 25 fps - the 'CRYS' switch I will convert into a mode that will give continuous ramping speeds much like your wind up ...

I also own a couple of Bolex wind ups myself (RX4 and a recently acquired SB) and am thinking rather than goin for a full blown xtal sync servo motor system like you are talking about building (?) I'll just use a stepper motor for that pesky range of speeds around 1fps to 10 fps - I'll put an encoder on of some variety just for a sort of speed read out, but no feedback (I personally would be the feedback mechanism in that case)

try also the forums at www.cnczone.com - heaps of info there
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#8 Olex Kalynychenko

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Posted 14 May 2006 - 11:03 AM

I'm doing some research on crystal sync motors and was hoping someone might have information and schematics. Anything would be helpful. I'm studying how they work from a component/electrical perspective. I'm fairly new to electronics so any techinical and schematic information would be really helpful.

Thanks so much.


What camera you wish modify ?
I can set crystal sync speed control module with microprocessor control on electrical motor of Konvas-2M ( 17EP-16APK ), Kinor-16 ( 29EPSS ) and other cine cameras with DC motor and tachometer generator in feed back.
Possible set this module on any other DC motor with optical encoder.
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#9 Bryan Darling

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Posted 14 May 2006 - 02:27 PM

I'm looking to build a crystal sync motor for my Bolex Rex-2 and to modify my Nizo 2056. I would love to be able to have sync speeds at both 18 & 24fps. I'd prefer to do it myself as a learning experience, although I more apt to have a professional do the Nizo if I don't feel confident.

I was thinking of getting the MCE-17B motor to use for easy applicatins where I don't need the xtal sync.

Nick, do you have any ideas on motors? What specs I should be looking for? Any ideas on make/model?

Thanks.

Edited by tornsprocket, 14 May 2006 - 02:30 PM.

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#10 Nick Mulder

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Posted 14 May 2006 - 04:39 PM

Nick, do you have any ideas on motors? What specs I should be looking for? Any ideas on make/model?

Thanks.



to answer that sort of question cnczone.com a *great* site (honestly) - mostly I pull motors out of defunct machinery or buy them second hand on ebay or surplus stores and have a play as buying them new is very $$$ - the main specs to look out for is the torque spec, which another visit to wikipediea will help you decipher what is it all about:

http://en.wikipedia.org/wiki/Torque

you will also need:

http://www.onlinecon....com/torque.htm as people will often try to fool you into thinking they have a super powerful/super small motor, however they have just provided you an odd torque spec that montgomery burns types would use..

also keep an eye out for its current drain as this will hinder your ease of designing the driver electronics, as for actual figures regarding DC servo type motors, you've kinda caught up with me!

The folks at NCS (http://www.intervalometers.com/) use steppers so they can easily stop and start the motor when the shutter is open and closed thereby being able to ramp from any speed to any other without aperture adjustment (with a little foresight and programming beforehand) - they use 'Vexta' brand which is pretty much a much of a muchness same as every other stepper clone out there (although I'm sure the differences are there, its just I've not tried every other brand and the marketing or lack thereof leaves me no other choice but to believe this at this stage) - look out for unipolar types which are easier to design the driver boards for (as opposed to bipolar and 5 phase) ...


Again an online tutorial is very helpful:

http://www.cs.uiowa.edu/~jones/step/

you can read as much as you like but actually buying some cheapo surplus gear and getting it going in front of you is a goldmine of tactile learning regarding the torque specification - you can try stalling it, look at its ramp/acceleration up to speed, try different power supplies etc...

look out for the specs online or hopefully they are printed on the side of motor ...

I got some big heavy 12v 3.5amp DC motors the other day for free from a ball throwing machine, in attempting to stall it I made myself bleed, very grunty things...

its stuff you learn by osmosis (pain) over time :P
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