Summary

Bracket to hold Maxon 137506 gearmotor (36 volt, 5 watt, 152 rpm) including a model of the motor itself. OpenSCAD file provided for modifications (maybe front face should be thicker?) Useful over a range of voltages: for example 15 rpm at 3.54 V (unloaded), and it keeps turning down to 0.2 volts (2 mA). The DC winding resistance is 60 ohms. It works as a generator also. It is not completely quiet, but it is less noisy than cheaper gearmotors. This one is available at some surplus stores.

The motor face takes 3x M2 screws, and the bracket bottom has holes for 4x M3 screws.