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Arriflex 16MB sync motor connector?

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I have been trying to outfit my Arriflex 16MB with a sync motor for music videos or similar (knowing how loud my camera is). I purchased a 60hz - 42v sync motor without its transformer for a reasonably low price on ebay. I shouldn't have any trouble building my own transformer but the connector on the motor is a little confusing to me.


Does anybody know what the pins are on these 60hz - 42v motors? I assume there is a ground, pilot tone, +/- 42v, maybe a secondary at 8vdc for the torque motor on the SB model?


Any help would be appreciated!!



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I'm no electrician but 42v seems like a LOT of power to be running through that camera. I have the Arriflex S/B with a 12v torque motor for the 400ft. mags but there is no connector or any port for one.


The only cable I have is a basic XLR that connects my battery belt to the camera on the (operator's) right side.

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This is an optional motor that plugs into the mains through a transformer. I have also used the variable and constant speed motors for this camera. My motors run at the original 8volts although i think many have been modified to work on 12v.

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I'm no electrician but 42v seems like a LOT of power to be running through that camera. I have the Arriflex S/B with a 12v torque motor for the 400ft. mags but there is no connector or any port for one.


Just some general info - AC synchronous motors in this application typically run on 110 volts, so 42 volts

isn't a lot, really. Their main advantage is that they lock to the drive frequency and maintain constant speed. However, they don't have a lot of torque. You have to make sure the motor is big enough for the load.


DC motors generate more torque, even though they run on less voltage.

Edited by dan kessler
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Just some general info - AC synchronous motors in this application typically run on 110 volts, so 42 volts

isn't a lot, really. Their main advantage is that they lock to the drive frequency and maintain constant speed. However, they don't have a lot of torque. You have to make sure the motor is big enough for the load.

DC motors generate more torque, even though they run on less voltage.

Okay, thanks for the info. I always thought most motors for those cameras ran off much lower voltage.

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Greetings David, Bill, Mark, Dan and any other forum members interested in this subject!


I have some information on the 24 fps sync motor that I can share. I am also an owner (and operator) of the Arri 24fps sync motor, 60~ (Hertz these days), 42 volts AC, 8 volt DC for magazine torque motors. I have used this motor with the Arri 16S camera as the motor was designed.


The thing to keep in mind, when this sync motor was designed for use with the Arri 16S camera, the 16M was not on the market. The earliest listing I have for this motor is a price list from 1961.


The motor was designed for use in the blimp for the 16S, but it could be used without the blimp. I never used my 16S in a blimp, so I have no experience with that set-up.


The 24 fps sync speed was maintained by the frequency of the mains, there were no xtal controlled motors back then.


This motor can be used on the 16M camera, even though there is no 8 volt magazine torque motor, you still need the 8 volts to turn on the 42 volt AC motor and operate the clap stick feature.


To answer a question, no, no 42 volts AC went into the camera (disclaimer: as long as the motor and cables were operating properly as designed!) The power supply is more than just a step down transformer.


David, in the picture of your 16M with the sync motor attached, I noticed that the motor was sitting further away from the body. That's when I realized, you have another Arri 'accessory' between the motor and the camera. That accessory is the 'Phase Shift Attachment' that was used for filming CRT tv screens back in the day. Description.....




I have never used this accessory, so I can't say how it works. But, the main thing is, when filming CRT screens you needed a sync motor so the shutter bar didn't drift.


So the previous owner of the motor used this on either a 16S or 16M camera to record tv screens. I'm assuming that this Phase Shift Attachment came attached to the motor when you purchased the motor.


The reason I bring this up, there are 2 conditions for using the sync motor and recording screens in the old analog days. Also, Arri offered a special sync motor modified for interchangeable geared heads to change the speed from 24 fps to 30fps for this purpose (it uses the same power supply as the 24 fps motor I talked about above).


One way to film the screen was, shoot 24 fps with a shutter at 144 degrees. Or, shoot at 30 fps with a 180 degree shutter, the mirrored shutter that came with the camera.


The special sync motor came with the 24fps gear drive, but you would have to send your camera to Arri to be fitted with a 144 degree mirrored shutter.


Or, you could keep the existing shutter in your camera and get the 30fps geared head for the motor, but you would be shooting everything at 30 fps, which may not work for sound synchronization.


You take your motor off the Phase Shift Attachment by loosening the clamp on the side of the phase shift unit. Pull the motor off and see which motor you have. Unless you are shooting old CRT screens, you really don't need the Phase Shift Attachment, also, by eliminating it, it would be 1 less rubber coupling that could be slipping on the camera's drive shaft.


The speed of the motor should be marked on the end where the drive shaft sticks out....




If your motor has the 30 fps gear head, then you'll be shooting everything at 30fps. You could always have the footage transferred at 30 fps. It's too late to find any 24 fps geared head assemblies, unless the seller included it when you bought the motor.


Does your motor have a pigtail lead on it as is shown on the right in this pic? It could have a connector like shown, or it could have a cannon connector such as the one that goes into your camera's power supply port.






Description of the 24 fps sync motor from a 1960's sales brochure. That is exactly how my motor and power supply look. I do have the accessory film counter for the blimp. That accessory also has contact points on the shaft that 2 wires are plugged into so when the motor is running it activates lights on the blimp that then blink so you know the camera is running.


As it states, the motor is 3 phase 60~ (c.p.s., the 'old cycles per second' term) 42 volts.




The accessory footage counter....




A newer Arri description of the 24 fps sync motor from the mid '70s (notice the smaller sized power supply).....




The 2nd paragraph in this Arri description lists the availablity of a 117 volt sync motor. I've never seen one, and I think that was a motor that Arri USA made for US customers, it's not from the factory in Germany. However, it seems with this motor, 117 volts went to the motor on the camera, but I'm not sure if you could use the camera's on/ off switch. Not much info on that motor is around. I guess the 'shock hazards' they mention in the previous paragraph about the 42 volt motor no longer exist when using this motor.


David, if you want to know which pins on the plug connect to the motor's windings, or the the 8 volt pins, I can make a plug schematic for you. The pins are not numbered externally. Of the 6 pins, 3 of them are used for the 42 volt 3 phase AC supply, 2 pins for 8 volt DC positive, and then one for ground.


I don't have schematics for the power supply.


So, in slow motion, this is how motor and power supply work on either the 16S or 16M....


8 volts positive comes out of the power supply via a seperate wire to the sync motor, it then travels out of the motor on the pigtail that is plugged into the left pin (the positive pin) on the 16 S camera's power input. The sync motor housing blocks the neg pin so you can't plug it in incorrectly. It then goes to the on/off switch. When the switch is activated, the 8 volts go to the torque motor on the 16S camera (not needed on the M model), the automatic clapstic on the GS models, and to the electrical contact on the sync motor (yellow arrow)...........




It then travels back (on it's own wire) to the power supply that contains 2 relays and activates those relays. When the relays are activated and they close the contacts, they connect the 42 volt 3 phase A.C power that travels back on 3 wires to the windings on the motor, and the camera runs.


When the camera is shut off cutting the 8 volts to the relays in the power supply, the power supply applies DC current to the windings of the motor to stop the motor from turning. It does stop the motor very quickly.


This dynamic braking is necessary on the 16S because of the torque motor on the magazine. When the 8 volts are cut, the torque motor stops right away, no more film is wound on the take-up side. Because the 42 volt AC motor is brushless, when the power is cut, it does not stop abruptly like a DC motor does, but it coasts to a stop. When the motor is connected to the camera, that coasting could advance the film movement and draw 5 to 8 more frames of film through the camera. The torque motor is stopped, so those extra frames of film cause slack in the film on the take-up side. When the camera is next started, the torque motor takes off, and depending on the condition of the clutch, it could pull on that slack in the film hard enough to strip sprockets and cause a lost lower loop, or break the film. Then the buckle switch works. If the camera is in a blimp, this would cause downtime, and the DP retires to craft services table. The Dynamic Brake prevents this.


I don't know why Arri used 42 volts for the motor. I have not run across any literature about why the engineers decided on this voltage, other than safety reasons mentioned above.


I have used my motor and power supply, not only on mains, but on location plugged into a crystal controlled generator. No problems.


I hope this clears up some of the mysteries of this motor!


























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Thank you so much Charlie for the very thourough response! This has definatly gotten me on the right track with this motor. I have been on-set the last few weeks and haven't had a chance to take a look at this untill now.


The phase shift attachemnt on my motor will have to stay on - I removed the caseing as suggested and the output shaft on the motor has been replaced by the long plastic accessory seen in the photo. On the output side of the attachment is the ball-like clutch connection but on the input side to the accessory is a gear that connects directly to the motor. The original output shaft was not included with the motor.




I removed the phase shift accessory by removing the caseing and then removeing the 3 screws seen in the second photo above.


It appears that the gear ratio of the accessory is VERY slightly less than 1:1. It took me some time to notice this because it is so slight but the attachment appears to slow down the output of the motor slightly.


My best guess would be that it takes the framerate from 24fps to 23.976 for recording NTSC systems?


As for the power supply unit - Charlie, do you have any idea how they manage to go from a 1phase 120v source to 3phase 42v? Also - inside the motor, I see 4 wires going into the windings but industial 3-phase motors only have 3 wires plus chassy ground - is this motor not a regular 'Delta' or 'Wye' three phase motor?


I am pretty sure I could create a powersupply/controller for this motor that chops a 42VDC supply at 60hz (120deg out of phase with each other) and provide the required 8VDC to the auto-clapstick and camera controls.


Thanks again! This has been a very good first experience on cinematography.com!!



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  • 2 weeks later...


I have some additional info for you about this Arri 24 fps sync motor set (Motor and Power Supply).
First, I don't have a schematic drawing of the power supply. I wish I did, I'd like to see how they achieved the 3 phase, and the 42 volts for the synchronous motor. Also to see how they switch in the DC voltage for the Dynamic Braking. I don't know where one would be available, other than at the manufacturer in Germany.
However, some things were easy to trace, and I was able to get some voltage readings at the power supply that may help solve the 3 phase mystery.
From the looks of your pictures, and with the casing removed ( blue arrow), you have the "special sync motor modified for interchangeable geared heads to change the speed from 24 fps to 30fps" that I mentioned in my last post. It also looks like your motor was set up to use on a "S" model camera by the pigtail lead (yellow arrow) that plugs into the camera's battery port.
Your motor with attached phase shift attachment was probably used on a S camera that had the shutter changed to 144 degrees for kinescope filming. If your motor was used on a "M' camera, the pigtail would have a Cannon plug to plug into the battery port on the camera. That way you could use the camera's on/off switch to turn on the a.c. sync motor.
It looks like this on S camera......
This camera has an extension pigtail added because the motor is set back further (yellow arrows).
You could make an extension with a Cannon plug for your M and connect the extension wire to the + pin.
close-up of the battery port on the S camera with the pigtail lead plugged into the + pin


With no motor in your camera, look at the back of your camera and into the motor cavity. At about the 6:30 position you'll see a flat copper leaf spring. That's the 8 volt positive supply that runs to your d.c. motor, such as the 'wild motor'. The camera body is the ground side (blue arrow). The silver end of the motor is the ground on the motor.
On the front of the 'casing' in your pic, there is a 8 volt contact point that lines up with the spring in the camera. (red arrow) (yours looks like it could use some cleaning :P )
Then the voltage travels through the 'casing' to a contact point on the front of the motor. In your pic, that point would be on the face plate, below the
red arrow. I can't see it because the drive shaft is blocking it. Looking in the casing (by the blue arrow) you should see something that makes contact with the contact on the motor.
Of course, all the locating pins must be lined up.
That contact point (the one we can't see) on the front of the motor takes the 8 volt circuit to the multi-strand cable coming out of the back of the motor, then back to the power supply.
To answer your question about the 4 wires coming out of your motor: "inside the motor, I see 4 wires going into the windings but industial 3-phase motors only have 3 wires plus chassy ground - is this motor not a regular 'Delta' or 'Wye' three phase motor?"
This is my motor with the cover off. The red wire you see is the wire for the 8 volt return to the power supply. It is just passing through the motor. It is not connected to the motor's windings. The 3 yellow wires are for the windings in the motor. The red wire goes to the terminal block, then exits on the blue wire (blue arrow) and connects to pin # 6 on the 6 pin connector (good luck trying to find those ancient 6 pin connectors).
The black wire (yellow arrow) is the chassis ground wire, also the ground for the 8 volt torque motor on the S camera via the camera housing and the ground contacts on the motor.
Put the phase shift casing back on the motor, and with your VOM, you can check the continuity by putting one lead on pin 6 of the plug, and the other lead on the contact point on the front of the phase shift unit. You should get a complete circuit.
The diagram for the pins on the connector....
Continued in next post............
(too many pics)


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I can't answer your question asking about the type of sync motor this is, 'Delta' or 'Wye' three phase motor? I don't have that knowledge, so I can't say. But, my curiosity got the best of me and I opened the power supply to see what's going on with this set.
I do believe the 3 phases are created with 2 windings on the step-down transformer and a 1000 uf electrolytic capacitor rated at 15/18 volts. Inside the power supply I found 3 large caps, one being the one I just mentioned, and the other 2 are for the d.c. rectifier for the 8.4 volts d.c., and the dynamic braking. Those 2 caps are: 40 uf +/- 10% (m) 250v /125v ~ 50Hz. But my motor says 60 Hz??
I did some searching and found a bit of info at Duall Camera, N.Y. about these motors. I believe Arri made only one sync motor, then put different housings on them, one saying 50 ~ / 42 Volts the other 60 ~ / 42 Volts. When 50 Hz current is applied to the motor, it turns at 3000 rpm. Put 60 Hz to it, it runs at 3600 rpm.
So Arri made a step down gear set with a ratio of 24:48 for the motor marked 50 ~ / 42 Volts to reduce the rpm to drive the camera at 24 fps. They had a gear set with a ratio of 24:60 to use with the motor that was getting 60 Hz to drive the camera at 24 fps. These gears are in the part of the motor that is inserted into the camera.
Looking at a sync motor, you can see the motor shaft, inching knob on the left, is off set from the shaft that drives the camera, it's not a straight line.
The speed of the motor is marked on the front. My motor is 60 Hz 42 volts 24fps
This is a motor labeled at 50 Hz with a gear set of 25/50 to drive the camera at 25 fps. You could run the motor on 60 Hz current, but it would drive the camera faster than 25 fps because of the gear ratio.
David, you said you saw the gear set, and thought that it might be driving it at '23.976 for recording NTSC systems?' I doubt it. These motors were designed in the late 50s, early 60s. Filming of NTSC systems, in 60 Hz land, was worked out to 24 fps with a 144 degree shutter, not a 145 degree shutter, nor a 143.5 degree shutter, but 144 worked. Of course, you would be filming only 1 of the 2 scans of the 2 scan video frames, so the video picture looked softer. The 23.976 came much later with crystal controlled cameras with 180 degree single opening shutters. That's a whole different discussion. But, the best way to check the speed of your motor and gear set, when you get your motor with the phase shift unit running, is with a cine-strobe on the shutter, or with a flicker meter.
Looking at the 'specifications' badge on the side of the power supply case, I discovered several things.....
The power supply works with a mains voltage from 110 - 240 volts. A switch is provided to select the input voltage. Mine is set at 110 volts.
The power supply works with a mains frequency from 50 Hz to 60 Hz. Does that mean one supply will work with either the 50 Hz motor or the 60 Hz motor? Seems to me that it does. I did see a cap in side that was rated at 50Hz. That would make looking for a power supply for your motor easier.
But the interesting spec was the 8 - 21 V. It does make the 8.4 volts d.c., but I thought it was 42 volts for the motor.

Inside the power supply on the relay side. You can see the 2 large 40uf caps for the dynamic braking.......


It is very difficult to trace the wires because of all the switching through the relays and the reversing switch. One really needs the schematic. I didn't want to disassemble it because it still works. Nicely constructed however. This unit was made in the mid 1960s.
The transformer side....
The back side showing the wires for the windings and the 3rd electrolytic cap (gray arrow lower left)...
The yellow wires on the left side of the transformer are for the different input voltages.
The transformer is a multiple winding transformer with 3 secondaries.
The top 2 lugs are for the 8 volt d.c. current, then the bottom 4 are 2 - 21 volt supplies. I read the output windings without a load on them. They were a little higher readings than the ratings, but my mains input was about 12 volts higher than the 110 input I had it set for on the trans.
How does it get the 3 phases? The 21 volt secondaries provide 2, one winding is the mains frequency, the 2nd winding is 120 degrees different because of the way its wound in the transformer (you'll have to read about transformers and multiple windings), and the 3rd phase is created with the 1000 uf cap.
Here are the readings I got at the power supply while the motor was running..... (I uncovered the connector to expose the 6 pins)
Between pin 3 and 4, 42 volts, Between pin 4 and 5 42 volts. Pin 4 I traced back to the 1000 uf cap's + side.
I can't explain how it works ! You'll need someone familiar with sync motors, maybe someone on the forum reading this has an answer.
I also can't say how the motor gets the boost to make it turn. At 1st I thought it had something to do with the relays, but when the 8 volts is applied to them, they both close at the same time. When the 8 volts is cut (camera switch), the top relay closes right away, the bottom relay is timed, and closes about a second later. During that time, the d.c. voltage is applied to the motor to stop it. Very clever.
I found this set on E-bay, you could get it for the power supply to drive your motor. lol
I've seen a lot of Arri S cameras for sale with the sync motor attached, with the 6 pin connector, but there was never the power supply included in the kit. Where did all those power supplies go?
Amazingly, my motor still works, d.c. braking also. It shouldn't, but it does. However, I can't control it with my iPhone.
Possibly Clive Tobin is still reading the forum. I would bet he would know about the wiring. I bought one of his TMX-22 sync motors to back-up this motor. lol.


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