Unfortunately, I'm going to have to shelve this project. The only working drive I had, an MPI Model 92 Quad-Density drive, stopped working today, and I can't afford to keep sinking money into keeping it operational. Parts for it are becoming increasingly scarce, especially with items such as the read/write heads.
I'm unable to precisely pinpoint the issue with it, but I believe the IR LED for the index sensor has gone bad. I did find a modern equivalent for it (a TIL34 IR diode), but after having bought an MPI Model 52 drive (essentially a Model 51 like what this project was to be centered around, but for double-sided floppies) that turned out to have multiple points of failure, I'm feeling very demotivated.
This entire journey has spanned several months, and cost quite a bit more money in parts than I expected, mostly due to my one existing drive failing in increasingly-frustrating ways. The logic boards of the 92 and 52 are still in fine working condition, but the mechanical parts--the drive assembly itself, which is much harder to come by and/or remanufacture, has put the cost of completing this project far above what I'm able and willing to pay anymore.
(Also I still have made almost no progress on redrawing the schematics because screwit I'm too tired for this anymore.)
I think I'll instead use the knowledge I gained from working on this in the meantime on something different. I've recently had the idea of a modern cassette-based data storage drive over USB on mind, just because I can.