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xkcd #2912: Cursive Letters
(imgs.xkcd.com)
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More like a typewriter, but instead of individual arms for each key, it was a wheel with all the letters that would spin to the correct position before a little piston would whack it. Also, yes, it was loud as fuck.
https://en.wikipedia.org/wiki/File%3AXerox_Roman_PS_Daisywheel_-_mono.jpg
Oh I've seen these... I thought they were for a typewriter, since they were among the things with the typewriter my mom had when I was a kid. Neat!
I have seen electric typewriters that used the same tech, so it may have been a typewriter wheel you saw.