Here's another design in the 25CUBE series (25 mm cube form factor - see https://www.thingiverse.com/thing:2927757). This one can spin easily https://youtu.be/-mPUYscmMzY although capturing the motion in a video was tricky. This thing was printed on a Form2 SLA printer in grey. I continue to be amazed at the details that can be printed with resin and a laser.
Some Assembly Required
After carefully removing the supports, sand and file to finish. Place gears and flywheel in the lower frame, carefully align the holes in the top frame with the pins in the lower frame and slowly assemble everything. A small drop of super glue on each pin joint will hold it together nicely. Rub mineral oil on parts to even out finish and lubricate the bearing surfaces.
Software and Tolerances
I designed this in Fusion 360. The pins are 1 mm in diameter and the holes in the frame are 1.05 mm. The shaft is 2 mm in diameter and the bearing support is 2.1 mm in diameter.