I join everyone here in welcoming you to the forum. I am sure your participation will be much appreciated.
Too complex for a small power machine like a Kinograph, and difficult to match speed with tension.
Inertia can be both friend and enemy to a system driven by impulses. whilst it can 'slug' the transient effect of the steps, it can also produce overshoot which can lead to 'ringing'. This is very evident in 3Dprinters and CNC machines where imperfections in surface quality can be the result unless run at reasonably low speeds and acceleration control is employed and optimised between steps. I have specific practical experience of this in my own 3D machine designs that I have worked on.
Now to consider what a stepped drive means in terms of the peripheral movement of the film on the take-up reel. Almost universally stepper motors have 200 steps/rev. At the periphery of a 250mm reel of film, one step equates to about 4mm of film. Microstepping the motor can reduce this somewhat, but at a considerable loss of torque which may mean a much larger motor needs to be used. If a motor is microstepped by factor 32, 90% of the motor's torque capability will be lost, yet the resolution in peripheral movement per step is still 0.125 mm (125 microns) which could relate to about 16 pixels at the image sensor for narrow gauge film. Yes, a gearbox could be used together with microstepping to virtually eliminate this problem, but now another problem emerges - backlash, which does not bode well with stepped drives because overrun caused by inertia is no longer checked.
Another problem with steppers is that their torque cannot easily be controlled. Even if it was, there a limits to how low it can be set before the motor starts to miss steps. If a gearbox (or belt-drive reducer) is used, then considerable high torques can be produced which could stretch or snap a delicate film if its free movement was impeded in any way.
If anyone considers using a stepper motor to drive something like a Kinograph on the basis that 'this is the modern way to do things' could be making a big mistake unless they are prepared to put some effort into understanding the principles involved, doing the calculations, weighing up the pros and cons, and backing this up with a lot of experimentation. If not, there could be a long road to trying to figure out why their machine is not the silky-smooth thing they expected it to be. They should also ask the question if a stepper would be be ideal to drive a record deck or a cassette/tape machine? (yes, there have been direct-drive turntables, but these were sinusoidal synchronous drives, not digital stepper motors).
In my view the Kinograph is best served by a transport drive which can be categorised as a 'steady state' system, where smooth speed and tension control are the main requirements over a relatively large range of reel speeds and varying inertia. My opinion is that DC motors (brushed or brushless) have so much going for them in terms of their inherent characteristics that for me the choice is simple.
And quite rightly so. They bring to the table a level of positional accuracy that a few years ago could only be achieved with extremely expensive servo control systems whose reliability was always questionable. Also, their digital nature aligns well with micro-controllers and their attendant software algorithms. The meteoric rise in production assembly robots is a testament to the use of stepper drives.
Last year I was involved in the design of a sun-tracker for solar panels, and a garden-watering robot that learned exactly what to water, for how long, and which varied its jet pattern and aimed it over a full 360 degrees in azimuth and 90 degrees in elevation according to what the user had demonstrated previously. None of this would have been feasible at reasonable cost without stepper motors (and an inexpensive Arduino to control them).
Yes, I am a big fan of steppers, but alas not for my own version of Kinograph I'm afraid.