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  1. #1

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    Cirkut #10 with electric motor

    There may have been more than one scheme to electrify Cirkuts throughout history, but here is a discussion of what I'm guessing is the most thorough and well-engineered one. I've seen two of them so at least at some point in time, this must have been THE solution to motorizing Cirkut #10s. I only have this one in hand to repair it, but I'll try to document it as thoroughly as I can while I have it.

    Basically the whole thing is driven from the governor end instead of from the spring end. The governor and its gear and the next couple of gears are replaced with an electric motor with a 27.9:1 reduction gearbox attached, and then a custom gear on the output shaft of the reduction gearbox. That drives the remaining two gears of the original geartrain from that side, and in place of the spring assembly is just a gear on a hub to take up the same dimensions for attaching to the drum drive shaft. I haven't counted teeth, but I'm assuming that big custom gear and hub has the same number of teeth as the original spring drum had, so the camera drive gear ratios will remain the same. The custom gear on the end of the motor/gearbox is bigger than the gear in that position in the original set, but of course it's calculated to provide a useful set of resulting drive speeds (which equate to shutter speeds.)

    Electrically it's all powered by a small PowerSonic Sealed Lead Acid AGM battery (currently missing, which is why I didn't picture it.) 12V, 1.4AH. There's a charging port on the side, plus an on/off/charge switch. On top is a 10-turn potentiometer with indicator knob so you can precisely set positions like 3.79. This feeds into a box with the guts of the drive circuitry. It's been sealed with goop (so nobody can copy the design) but I'll figure out what's in there once I get it running and hook a scope up to it. I'm assuming it's just something like a 555 timer and a motor driver IC, so the motor gets pulsed to vary the speed, rather than varying the voltage (which would lessen the torque at slower speeds.) But I'll add to this thread once I find out for sure. The pictured one seems to just replicate the original speeds, but with the (theoretically) more reliable electric drive motor instead of the spring would governor setup. Brad's other camera was definitely set up for much much longer effective shutter speeds. From memory I believe it went from 1/5 of a second to 9 seconds. That was probably accomplished with different component values inside the gooped box. You could argue about whether there was any need to just replace the simple original gvoernor motor with an electric one, but allowing 9 second shutter speeds is a no-brainer justification for doing it!

    In addition to the custom gears and the insanely expensive Swiss-made motor and reduction gearbox, some serious effort went into the mounting plate for the motor itself. I figured it was just an adapter plate pinched in there with the original nuts, but it's actually spot-welded together!

    Underneath that plate is a little microswitch to turn the motor circuit on when the original camera switch is flipped to the on position. Looks like it uses what's left of the (former) brake actuating lever to accomplish that. There's also a little jack there to allow easy disconnection of this switch from the camera wiring if you want to remove the whole motor assembly. Similarly the motor itself has a disconnect jack. That was nice of them! On the bottom of the camera is a big multi-pin jack that is not now, nor has it ever been, connected to anything. I have no idea why it's there. Brad's other camera doesn't have this jack. Abandoned idea? Just something to fill an extra hole? Over near the hub drive side of the motor assembly there is a short bolt with nut going through a hole in the bottom of the plate which is clearly just there to fill the hole left when they drilled out the axle for the spring ratchet pawl.

    OK, enough yammering, enjoy all the pictures! (The limit is 10 so I'll put the last 3 in the next post.)

    Duncan





























  2. #2

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  3. #3
    paul_c5x4's Avatar
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    You planning on copying the mechanics and retrofitting your Cirkut ?

  4. #4

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    Quote Originally Posted by paul_c5x4 View Post
    You planning on copying the mechanics and retrofitting your Cirkut ?
    Well I admit that one reason I wanted a parts camera was to possibly play with alternative power options. The MacGyver in me thinks that the last 100 years must have provided better options for this. But the more I play with the governor camera, the more I wonder. I mean, there's a reason people kept using these camera as-is until the bitter end; nobody ever designed something to replace it while using the same film. It's basic, but it works, under most conditions.

    Having said that, there are some cases where the motor drive would have an advantage - cold weather (I'm guessing...except if it's cold enough for the battery to stop working), nighttime long exposures, remote activation. But for me, I don't think that's enough to start messing around with "improvements" at the moment. I need to go get experience using the camera as it is, and the weather here is starting to warm up so maybe I can do that.

    My engineering mind is very interested in this stuff, thus my fascination with exploring and documenting this existing motorized Cirkut design. For someone trying to copy this approach pictured here, there are some big hurdles. There is no question that the big gear and hub drive for the film takeup spool has to be custom made. It looks like the gear on the motor is custom made, though maybe you could find something off-the-shelf. That exact motor and gearbox combination looks to no longer be available, but similar setups appear to be expensive - like $500 or more. And you need something pretty powerful to do it that way, so you can't cheap out too much on the motor. In my pondering the problem, I was actually imagining that the last 25 years since this modification was made would provide even more options still. Like, what if you had two motors, under computer control. One drives the film takeup and one drives an output gear that meshes with the gear head. You dial in the details like shutter speed, focal length and focus distance, and the computer drives the two motors at the appropriate speeds to give the perfect picture. No more needing to carry a dozen gears, needing more gears when you get another lens, no more accepting a gear that's "to the nearest tooth" - the ratio between speeds could be exact.

    ...but I don't think I'll be attacking that any time soon. There's too much I can do right now with my camera as it is, and I'd rather be shooting than tinkering.

    Duncan

  5. #5

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    Just for the benefit of future google searches, I will add that this appears to be the "Paskin conversion" done by David Paskin years ago.

    I'm waiting on a couple of connectors to repair the broken one from the switch, and to adapt the charger to the port on the side, then I'll be able to test it out briefly and figure out how it works, before returning it to Brad.

    Duncan

  6. #6

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    OK it's all fixed up and boxed up and heading back to Brad, but not before I put an oscilloscope on it for a bit. I continue to be impressed with the engineering that went into this conversion. It basically varies the voltage to vary the speed (I guess the reduction gearhead allows it to maintain sufficient torque even at lower voltages) but it's not that simple. It is using some sort of circuit to try to maintain a constant speed on the motor under load. They used to make dedicated ICs for this (like, for use in old cassette recorders) or he could have done it with discrete components, but the basic idea is to compare the current through the motor and the inferred voltage drop across the windings (which is an indication of back-EMF) and thus be able to compensate for motor load. In addition to the basic voltage being applied to the motor, there is also an additional series of pulses designed to maintain the speed. More load, more pulses. He probably could have gotten away with just varying the voltage to vary the speed and ignoring the load component since once you figured out where your settings needed to be for what exposure you wanted it wouldn't change much from roll to roll, but this takes all of that uncertainty out of the picture entirely. This really is a well-thought-out piece of retrofit engineering.

    Duncan

  7. #7

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    yahoo has a panorama-group. there are cirkut experts.
    www.3dreal.tk
    www.stereopan.tk
    3dstereoaeropanorama
    swiss alps
    3ds-marspanorama temporarily gone



 

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