Sounds like a fun project! First, pick a single‑piece lens—an old C‑lens will give you a good focal length and decent aperture for a clear image. For the gear train, the projector needs a step‑down from the motor’s RPM to a slow film advance. A 3:1 ratio on the main drive and a 4:1 on the shutter wheel usually works; that gives you about 90 fps of film motion for a 24 fps run, leaving room for adjustments. Keep the lens‑to‑film distance exact—measure with a ruler and use a small spacer block to lock it in place. Once you’ve set the lens, crank the motor and fine‑tune the shutter timing until the picture is crisp. Don’t rush the alignment; a tiny misstep in the gear mesh can throw the whole thing off. Good luck, and let me know if you hit any snags!