Off and on for years I've been wondering how to maintain a data connection when one side of the connection can rotate arbitrarily, without limiting the number of degrees through which that side can rotate or tangling the wires.
I finally looked it up and, huh, the idea I'd had in my head for how to do it turns out to be the state of the art: http://www.homebuiltrovs.com/slipringreel.html
("Just go wireless" also works, but introduces its own set of problems.)
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