[msandford]

And ideally not just using an encoder to detect skipped steps or something. But using some kind of vision to close the loop using color since you're making an image.

At the very least put a Gray code on the back of every fabric loop to get actually accurate positioning.

[joezydeco]

Coding on the underside crossed my mind too, but then you'd need a multi-sensor tx/rx board for each ribbon, mounted inside and under the moving parts. And it looks like this mech doesn't have a lot of space to begin with.

[msandford]

That's why using a high res camera to image the entirety of the spools and make adjustments as necessary seems like the best way to close the loop. It won't be able to make minor adjustments but if something is really wrong it wouldn't be hard (algorithmically) to locate which spool is totally bonkers and get it much closer to right.