CHEAP or EASY String Pots (source, or fabbed)

[kmcclary]

String pots (aka "yo-yo pots") are occasionally mentioned as a sensor possibility, that could solve a whole class of problems (see closed thread http://www.chiefdelphi.com/forums/sh...ad.php?t=43479 ).

I've seen people posting links to lots of expensive commercial sites, but I've YET to find a decent fab diagram, or a cheap source of them (more like $20 vs $200 apiece).

BTW, I'm mainly interested in a 25" string pot... Either a VERY cheap source (commercial ones are often well over $100), or a simple way to fabricate a 10-turn or 15-turn pot add-on (consisting of a bracket, a non-binding drum reel, and a constant force spring), that can accept a COTS 1/4" shaft multi-turn pot.

Has anyone cracked this problem yet, by either finding a cheap source, or a way to SIMPLY make a reliable one? Linearity is not as important as *repeatability*. We can easily calibrate for non-linearity in software, but no overwrapping of the drum at all can be allowed.

- Keith