In regards to the frame float issue when using a stepper motor, I do believe this can be completely compensated for in software. Basically, you accumulate the error as (in fractional steps) and always output the number of steps that minimizes that error. If it’s a geared stepper, it’s best if you can determine the exact gear ratio. I have tried this with a geared stepper that has a known fractional gear ratio. With error compensation, I can step the motor through thousands of revolutions and observe that the shaft stops at the exact same angle it started from.
That sounds like the approach used in the Pi telecine project. He set the camera to capture a bit outside of the image frame and then somehow compared the position of the current frame to the position of the edge of visible area. He then fed that back to the program to adjust how far the stepper motor should turn.
I’m guessing this is mostly an issue when using the motor to drive the take-up spool directly. If you had the motor moving the film across the gate, then you should be able to make fairly accurate predictions of how much to move the film, since the motor only needs to turn the amount of each frame. In that approach, though, I’m assuming you’d need separate motors to drive the take up and feed reels.
Granted, a bit late to respond…
I am using 3 motors, one for each reel (DC motors) and a stepper motor to drive the film.
Hi folks,
I’m hoping I may have chanced upon a topic that aligns well with the data points in this thread.
I recently wrote an email to Bill, who made the projection video, but no clue if he’ll actually repo d or not.
I also saw someone above joke about getting access to a moviola. Sadly, looks like most of those are in California.
On to my project/inquiry… it’s not exactly Kinoscope in nature.
I recently went to a garage sale a bought a few 35mm movie trailers from a fellow that owned a cinema in the 1980s. I’d love to find a way to play them (sure it would be easier to just pipe the tiles into YouTube but who likes easy?)
I did the eBay thing but 35mm cinema projectors are still a fortune. I do however have 3D printers at home, a local makerspace with laser cutter and even a small forge that might be able to produce lost PLA metal parts.
My issue is that Bill’s animations are all for 16mm and I have no clue how to come up with the specs for 35mm. I could either try his design for transport or the geneva mechanism. I’ve been searching instructables, thingiverse and grabcad etc… but haven’t come upon anything useful to date.
Does anyone here have any thoughts/recommendations for me? I have a good suspicion that this project should be very doable for me to get something simple projected against a wall at home.
Thanks in advance.
Sounds like a fun project! I did some quick searching around for a portable 35mm projector because I swore Kodak used to make one, but all I found was the Pageant 16mm version.
The most difficult part will be the intermittent motion. Perhaps you could buy a gate on eBay that includes the gear train for that?
You could use the optics from a slide projector and maybe even the light bulb setup too.
It actually sounds like a pretty difficult project to me, but I’m hoping you keep at it so we can see what you come up with!
Here are some interesting finds on eBay:
Thanks Matthew.
I’ve been looking at eBay myself but weight and distance usually play a big factor here. I may but a msall hand crank unit just to harvest the lens itself.
Does your own setup have an intermittent component or are you doing that in software with the motors?
As it stands, I do have quite a lot of extrusion sitting here but was a bit concerned about the overall expense in motors.
Thanks.
@WirelessGuy_NY sorry for the late response. I was moving!
My setup does not have intermittent motion. I hope to detect the frames electronically or with computer vision and take very quick photographs as the film passes in front of the camera.
Motors are an expensive component! I have chosen these for my new design (which I hope to document more publicly in the coming weeks):
1x GPN9 for the capstan drive that pulls the film
2x GPN12 for the feed and take-up reels
Interesting read about the accuracy of microstepping and a comparison of the performance of certain drivers: How Accurate Is Microstepping Really? | Hackaday
The Allegro A4988 on a Pololu-like stepper driver breakout board seems to have performed the best…