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Comment by mendelk | Hacker News Reader

Re the self-correction, perhaps it's this:

> Each ribbon also features a reflective strip which is scanned by an infrared sensor, which tells the machine the color each spool is currently showing, allowing for corrections for any slip that may occur.

Source: http://breakfastny.com/f21-thread-screen-press-release

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That's badass. I wondered about whether the machine would need constant calibration due to the belts slipping or hopping a gear, etc. I really dig solutions to problems like this.. I'm not sure how I'd categorize them, I suppose solutions that involve observing reality as directly as possible instead of relying on too many layers of abstraction.

EDIT: I guess now I'm curious... probably this is fast enough that you can literally scroll until you see the right color. I wonder if that's what's happening or if there's still an attempt to remember where on the belt it's located and make an attempt to take the fastest path there. It'd only be faster half the time though. I wonder if the overall experience would differ much.

Having to know where you are (and how far you move when you turn the spool) requires a stepper motor, which makes everything more complicated. This way you can just use a normal DC motor, and stop when you reach the right point. And since spools probably slip a lot (given they're not designed to keep things from moving), the stepper solution might just fail completely, since it wouldn't have much confidence in what it thinks is showing.

This is what I was wondering. My theory was that they were using a camera looking at the front of the display to identify the color being shown by each spool. I think my solution is better :)

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