I've designed and built this shifter almost two years ago. It's been working great ever since, however as a publicly available project it's lacking documentation, but I will try my best to improve on that.

Features:

-Uses only printable parts and common hardware like linear bushings and bearings.
-R+6 layout. Reverse gear is next to the 1st. To engage the reverse you have to push harder to the left, like older BMWs.
-Adjustable spring preload for both side-to-side and gear-to-gear axis.
-For registering position it uses two potentiometers, joystick style. Possibility to change at which point the gear engages as a button in the arduino code.
-Arduino Pro-micro controller as HID device. Programming code has calibration instructions in the comments.

I printed everything from PETG with 0.2mm layer height, 4-5 shells and top/btm layers, 25% infill or so.

Notes:

-the stl files are not pre-oriented for optimum printing. TBD.
-assembly drawings and instructions are not comprehensive. TBD.
-wiring is two pots to two analog inputs of an Arduino pro-micro. A comprehensive wiring diagram is TBD.
-Calibration process is described in the arduino sketch comments. A more comprehensive writeup is TBD.
-BOM might have some errors in the per-assembly descriptions. Overall materials and quantities should be accurate however.