SnailScanToo or 2

[PM490]

Small progress, the initial testing of the transport components working together, controlled by the Pico is going well.

This video shows the supply and pickup working and holding tension, and the capstan moving the film precisely. Scanner is running with the short-pitch 7.605 mm, the capstan steps (with the TMC2208 micro-stepping) are 15,346 per frame! Snailing slow, as expected.

Testing SnailScan Transport

Here is the resulting test of the dancing-pot tension (using a spring-scale for calibrating).

The potentiometers are wired mirrowing eachother, what keeps the log curve about the same for supply and pickup (using log potentiometers, what I had). The tension used for the video is 1N on each side.

One item unexpectedly found was that the Pico ADC external reference is somewhat particular. When applying the 2.5V reference, common to the potentiometers, the Pico was having power-up issues. The problem is that it uses a small resistor (R7) as bridge between 3.3V and the VREF, and the 2.5V was affecting it. This is referenced in the Pico datasheet, and as suggested there, for this use case is was best to remove R7, with the added benefit of isolating the ADC reference from the 3.3V digital noise.

@friolator

This is not unlike the Imagica 3000V transport. It was a scanner from the late 1990s - very slow - designed for digital intermediates. If you think your scanner will run slow, remember that the 3000V took 30 seconds PER FRAME to scan 35mm at 4k! I had one of these as the basis of my first conversion project, but ultimately moved to a different platform. but the basic transport is not unlike your new layout:

Thanks @friolator for the reference to Imagica. Based on the initial results, while SnailScan is extremely slow, should be 5 or 6 times faster.

@robinojones

Nice and tiny design ! - your machine is starting to have soviet space program aesthetics

Thanks @robinojones. The transport (without the camera) has a similar form factor of a tape reel. The motors are spaced to accomodate 7" diameter reels, which I have a few of 8mm. The video shows 3.5" diameter reels for the 16mm film.

Thanks to everyone for the feedback, small steps (snail steps ). Stay tuned!