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DIY Crystal Sync Motor?


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#1 Jay Taylor

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Posted 19 August 2008 - 11:44 PM

Hey guys,

So this is probably over my head, but has anyone ever built their own crystal sync motor?

I have a Fries Mitchell, so I'd like a motor that could do 1-120 fps, all crystal speeds. How are most motors built? Do most use some sort of DC servo's, or something else?

Like I said, probably over my head, but I'd still be interested in learning how motors are built.

Jay
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#2 Paul Bruening

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Posted 20 August 2008 - 12:25 PM

Bruce McNaughton built my Fries motor. It is muliti-speed in 100ths increments. So, it can handle all those strange flicka' (you know, my friend, Flicka?) speeds. As I understand it, it's all servo motors and stepper motors these days with digital controllers. Clive Tobin makes motors and controllers. I assume he's digital since his motors have precise control resolutions. I do know digital is easier and has more, precise controls than crystal.

I guess I should ask, how handy are you with motors, controllers, writing controller code, machine tools, soldering wire, etc? Because these kinds of projects can get pretty involved. Another thing is, accept that it will take a few prototypes to iron out unforeseen problems. Guys like Bruce have piles of conceptually flawed prototypes laying around. They don't let a product out the door until it has been refined to a well tested and working model. I have a small pile of parts and pieces to my DIY scan rig in a box from ideas that just didn't pan out.

I'm not telling you, "Don't do it," because I'm a, "Give it a try," kind of guy. But I am saying you could save yourself a lot of head scratching and cussin' if you get something already worked out by someone else who does this stuff for a living.
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#3 Jay Taylor

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Posted 20 August 2008 - 03:04 PM

Hello,

Paul, I sent you a PM.

The only thing I'd really be worried about is having to program the controller. As far as just hooking up a servo to the camera to make it go, it's probably not too big a deal. But programming it for different speeds, intervalometer functions, and all that? no clue.

I know I sound naive, but I'm sincerely interested in figuring out how this stuff works.


Jay
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#4 John Sprung

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Posted 20 August 2008 - 06:03 PM

I did build a demonstration unit about 30 years ago. IIRC, I just barely got it to work once before I fried something in the electronics. Back in those days, the idea was to use a CMOS 4046 phase locked loop chip to lock the frequency from a light chopper disc on the shaft to the crystal by pulse width modulating the power to the motor. So, you had to run the motor thru some hefty switching transistors. IIRC, I used 9.6 KHz as the pulse rate, so the thing made audible noise under load. The tradeoff is that going to a higher frequency means switching more often and making more heat in the power transistors. Going below the audible range would give you mechanical chatter.

I started from the schematic for an early CP crystal motor for the Arriflex. I just happen to have pulled the paperwork out on that, since I got a request for the schematic. They ran at 576 Hz and made their own PLL out of a quad nand gate.

Today, stepper motors could be driven at the chosen rate without the complexity of a servo. In any case, a crystal will still be your frequency standard.



-- J.S.
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#5 Olex Kalynychenko

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Posted 21 August 2008 - 02:42 AM

Hey guys,

So this is probably over my head, but has anyone ever built their own crystal sync motor?

I have a Fries Mitchell, so I'd like a motor that could do 1-120 fps, all crystal speeds. How are most motors built? Do most use some sort of DC servo's, or something else?

Like I said, probably over my head, but I'd still be interested in learning how motors are built.

Jay


I upgrade of many type of DC motors of cine cameras on crystal sync speed.
Give me more technical inforation about your motor, pictures ( on personal e-mail ).
What kinds of type of motor ?
The motor have any feed back ? digital, optical, analog, taxo ?
What kinds of camera you will use ?
You have any mechanical parametetrs and characteristics of camera ?

P.S
The Micropower Phase-Locked loop chip 4046 - the design of past century.
Yes, this is very good chip and can be use, but, the procedure of signal conversion of chip included many procedures of calculation of analog quantity.
The modern algorithm of PID speed control inclued more wide rate of parameters and data and have more high accuracy of control.
This is like, if i will compare of compact calculator and modern Personal computer.
Any case, this is my personal opinion and personal experience of research.
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#6 Hal Smith

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Posted 21 August 2008 - 10:13 AM

Crystal motors are digital, just as not elaborately so as stepper motor and microspeed controllers. There are some real difficult design criteria in motor control. It's not enough to just control the motor's speed, there are all sorts of issues to be addressed like ramp up to speed, braking, tendency of servo loops to "hunt" back and forth past the desired speed, etc.

I'm about to build a controller and power supply for an Arriflex 3-phase blimp motor. But I'm not going to start from scratch, I'm going to try to modify a commercial 3-phase variable speed controller to run at crystal speeds. That way I'll inherit all the work that supply's designers had to solve with respect to generating the 3-phase AC power and making that circuitry reliable.
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#7 Jay Taylor

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Posted 21 August 2008 - 10:30 AM

Hey everyone,

Hal, I've consider a lot of the things you've mentioned. Ramp speed, braking, etc. I've also read a lot of arguments over servos and steppers.

I guess I'm oversimplifying, but the controller itself would be responsible for timing, and that's it. The speeds, the ramping, braking, it's all timing. Sounds simple in concept, but I realize it's probably quite complicated in practice to build a controller capable of all that.

Another type of motor I had in mind would be responsible for the variable shutter. Something that would allow to program fades and dissolves. I'm assuming with something like that it would need to be synced somehow to the main motor. This getting into full blown motion control territory!

Well, is there anyone you guys would recommend that builds these types of things for a living?


Jay
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#8 Jay Taylor

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Posted 22 August 2008 - 01:47 PM

Hey guys,

Okay, trying to simplify things a bit. Rather then being able to punch in any speed to two or three decimals, I decided to have about ten preset speeds ranging from 6 to 120. I could use a rotary switch to select the speeds rather then some sort of numeric pad.

Would it make it easier if only 24 were crystal, or would it be no more difficult to make all speeds crystal?

As far as ramping is concerned, could there be a flat rate applied to all speeds? Each ascending speed would then take slightly longer to ramp up then the previous speed. Of course, how is this done?

I'm assuming you'd want a servo connected to the 8:1 gear shaft, which would require 900 rpm's for the top speed of 120fps, and each frame would require a turn of 45 degrees. I suppose you could have the motor connected to the 1:1 gear shaft, but then you'd need 7200 rpm's for the top speed. Wouldn't vibration be a problem at that speed?

So what I'm imagining, as far as the controls are concerned, would be three rotary switch's. One would be for the live action speeds, 6-120.

I suppose you'd have a switch that would change the control to the second rotary switch, which would be for single frame exposures. It would also have about ten settings from 1/8th of a second to 1 minute exposures.

Then there could be another switch/button that would activate the third rotary switch for the interval settings. I'm thinking about 12 selections from 2 seconds to 1 hour.

Then you'd need a power button, a switch for reverse running, and a start/stop button. Also, a power connection, and an outlet for possibly a remote.

Sound feasible?

I thought that you could have two separate motors inside the casing. A servo coupled to the 8:1 shaft, and a stepper attached to the 1:1 shaft. That way when you enabled the single frame control, it would change over to the stepper. Of course, I'm not sure if you could fit two side by side given the small amount of room. Also, I'm thinking it may not be possible anyways due to one of the motors being stationary when not being used. Would this cause some drag, forcing the working motor to compensate?

Alright, tear it apart if you want, or suggestions on how to make this a reality!


Jay
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#9 Hal Smith

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Posted 23 August 2008 - 09:04 AM

Do you have access to a machine shop? From my perspective, 95% of any serious modifications to a camera or home-made accessories always ends up requiring a machinist who knows their way around precision machinery. I was connected by family for a few years to Cadillac Motor Division's retired chief tool and die expert. Unfortunately he's no longer with us - another of America's Finest Generation gone to their eternal reward.
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#10 Paul Bruening

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Posted 23 August 2008 - 04:20 PM

Hello Jay,

I am definitely in favor of you learning this stuff. At the same time, what is your goal? Do you want this gear because you want to make movies or do you like widgets and technology. James Beverly and I have chosen the path of self-equipping because we want to make movies. But, when you think of the time we've spent getting equipped, we could have actually made at least one movie if not more.

What do you really want to do?
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#11 Jay Taylor

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Posted 23 August 2008 - 05:43 PM

Hello,

Hal, I will need to find someone who has the equipment and expertise for any of my machining needs.

Paul, I've been interested in learning electronics/motion control/animatronics for quite a while, but like I said, very limited experience with any of it. I'm wanting to learn this in order to aid my film making endeavors.

After talking to a few people I'm starting to think you can't have a motor capable of high speed, and single frame/intervalometer functions, but certainly it's possible.

The Lynx C-50 can do this (with the optional quicksync controller), the Fries motor can do this (with the intervalometer remote), the Jackson Woodburn can do it with all functions completely built in!

The Fries is a dc servo, I'm assuming the other two are as well. Would they be coupled to the 1:1, or the 8:1 drive shaft?

First thing I'm trying to figure out is what kind of motor (servo or stepper), and which drive shaft to couple it with.

http://www.tobincine...com/page14.html

That article claims steppers can be hard on a cameras gears. Of course, everything else I've read suggests that creating circuits to control steppers is quite a bit easier. So?

I realize I'm at the bottom of a very steep hill.


Jay
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#12 Jay Taylor

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Posted 04 September 2008 - 08:16 PM

Hello again,

Does anyone know of any forums that might discuss electric motors, and how to build them?

I'm wondering if there would be anything wrong with having a dc servo coupled to the 1:1 drive shaft if I intend on shooting at high speed. I figured that would be the only way to have a motor capable of high speed, and single frame/intervalometer functions. Although, if making two separate motors would be way easier, I have no objections.

Any resources on writing code for the controller?

Would it be best to use an eprom, or a microcontroller? Or something else?

So many questions. Having a hard time finding the answers!


Jay
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#13 Jay Taylor

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Posted 15 September 2008 - 07:23 PM

Hey again,

Not much discussion in here! I'm not surprised. This motor business is super complicated.

I stumbled upon an old thread over at the stop-motion message board. Someone built a single-frame/intervalometer using a superior electric stepper motor, and a stepper controller from applied-motion. The controller comes with some software to help program everything, and the person that did this posted a video showing how the software works. Looked quite non-programmer friendly.

Anyways, applied-motion also carries servo controllers, which include the same software. However, the specifications for the software claim that only 8 inputs are programmable. I'm assuming, in the case of a live action motor, I'd only be able to setup 8 speeds. Is this correct? I had worked out ten speeds I'd like to use, and now it looks like I may have to take another couple off the list.

Out of curiosity, how are the old mitchell "wild" motors put together? Of course, those are AC, so that would probably be too dangerous to mess around with.


Jay
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#14 Paul Bruening

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Posted 15 September 2008 - 07:34 PM

I wish I had answers for your q's. I do know this, servo-motors are often used for continuous speeds even if those speeds can change incrementally via an encoder. Smoothness is the reason. Steppers are great and certainly perfect for stop motion. But they wobble. Some, a lot. They can shake enough on a lighter camera to effect the image quality. Bruce put a whopping big, rare earth, stepper on my scan rig. But, the camera is mounted to an even whoppinger big chunk of steel to eat the vibrations. It would be no good on a tripod. Unless something has changed over the last few years, servos are used for continuous speeds and steppers are used for intermittent speeds. It may be beyond motors to do both for you without some other compromise.
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#15 Dominic Alt

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Posted 15 September 2008 - 11:53 PM

Bruce put a whopping big, rare earth, stepper on my scan rig. But, the camera is mounted to an even whoppinger big chunk of steel to eat the vibrations.

Is your scan rig an Arri II or similar? And did he put that whopping big, rare earth, stepper on the 1:1 shaft?
If so, that was a big whopping mistake. When you use a stepper, the torque of the motor must be matched to the torque of the load. The 1:1 shaft of an Arri is a light load.
Replace the whopping big motor with a smaller motor and you'll be much better off. Maybe it won't pass the penny test, but it might pass the nickel test. :rolleyes:

The Nickle/Penny Test

Posted Image

Edited by Dominic Alt, 15 September 2008 - 11:54 PM.

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#16 Paul Bruening

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Posted 16 September 2008 - 12:43 AM

Mitchell NC. Have you seen any of the old NC motors? They're just about as big as the camera body. Bruce's stepper is tiny compared to the old DC motor I've got for it. It's almost as big as an American football.
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#17 Paul Bruening

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Posted 16 September 2008 - 12:57 AM

The Nickle/Penny Test



Oh, I see, now. You didn't even ask what camera I was using before putting me down. Jay asked how he could do it himself. Not if NCS could sell him one.
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#18 Dominic Alt

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Posted 16 September 2008 - 02:20 AM

Oh, I see, now. You didn't even ask what camera I was using before putting me down.

No offense intended, either to you or Bruce, but that would be my remote diagnosis.
In any case, Mitchell or Arri, basically the same thing. Not much torque is required.

If the vibration is a problem, try a smaller motor, or less current through the motor. If not, no need to change anything.

I've only seen the old motors in pictures. Very impressive. When running at normal speeds, it is nice to have a giant motor for fast acceleration. I'm not sure what size magazines were used with those cameras, but I think 1000' magazines were available. That puts a load on the camera.

I just bought a wild Mitchell MKII motor door. The attached motor is 1/6th horsepower! Not football-sized but it is bigger then a soda can.
I will be replacing it with a much smaller motor, but for single-frame only. No sync.
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