Apparently there's this great thing out there for linear motion called a roller pinion. It has all of the advantages of a rack and pinion for simplicity, but it'also precise, has low backlash,is efficient, and quiet. I spent some time trying to figure out how to derive the profile. I believe I'm really close to the right profile. I'm hoping others can help me make it a real thing. It would be nice to use these for anything that needs precise linear movement. I'm thinking that for the rollers you could use smooth rod and some brass tubing from a hobby store (for bushings). Here is some of my reference material. ecnmag.com/articles/2011/07/hardware-corner/roller-pinion-tech/ nexengroup.com/nxn/files/pdf/966650s.pdf

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roller, pinion, linear, motion, scad, openscad