I thought I’d toss up pics of the grain mill that I just motorized using a 90-VDC motor. Unlike AC motors, you have to use a power supply to control a DC motor, and on e-bay, gear motors that have enough torque at the slow RPM’s needed (i.e. more than 40 in-lb at 120 RPM or above) seem to be much more common in the DC variety. I picked up a used 90 VDC gear motor at 120 RPM with 50 in-lb of torque off ebay for about $25 and attached it to a Monster Mill 3 using Flexible Spider Shaft Couplings from McMaster Carr (I stole the idea from Chris Solito). You can run the motor using a plain 90 VDC power supply but these often how low current limits (i.e. 0.5 Amps) while my motor draws 1.23 A, so I opted for a KB motor control, model KBWM-120 with a 1.5 Amp fuse. These are fabulous controls because they come built-in with a power switch and speed control. You attach the four wires (two for the motor, two from the wall) and badabing! good to go. This was $80 on ebay, and while cheap knock-off versions from China are available, I trust KB electronics. $2 in scrap lumber from Home Despot, $16 in bolts and clamps from ACE Hardware, and a few minutes of jigsawing and it tore through grains in no time. I tested the mill with the hopper filled up before turning it on and it worked just fine.
Here is the finished product, with close-ups of the individual parts below.