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
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
I don't get by here much these days, but the system emails me if someone sends me a message.