I didn’t realise the huge amount of posting there is when it comes to the drive system on here going back to 2016. I’m more confused than ever, and the ideas seem to be bouncing between so many different motors and solutions.
I’m hoping someone could correct me if my guess for my own scanner is wrong or has any flaws please
For my own little 8mm film scanner, I’d like to use cheap geared DC motors with an encoder that would be direct drive.
On the supply side I’d add a dancer arm held by a spring with a high resolution encoder or a pot to give feedback to the motor algorithm to slow or speed up the supply motor only
The spring tension would be adjustable, I don’t know if it’s necessary to have something like a solenoid controlling it.
I’d drive the take up motor to keep the film flowing at a set frame rate (16,18,24,25 etc) by measuring the film speed by a roller(either PTR or printed plastic roller with sprocket teeth) mounted directly on a rotary encoder.
I’d hope to add a magnetic sound head in line which is why speed would be important.
I can’t totally see the need for a capstan if the take up reel is spinning very evenly. Those dc gear motors seem to have a lot of inertia and don’t fluctuate much, but maybe the take up reel might not be spooling very evenly and will cause slight flutters in speed.
Or maybe there could just be a roller with a large flywheel from an old projector?
Here are a few YouTube videos I found Wind/Unwind Machine - YouTube