... Oh man, I wish I knew what any of that drawing meant? I'm sure it's something awesome! I did this, literally don't know what I did, but it worked! I'm all electronics dumb and stuff.
If the
ladder diagram offered by
@Tha fios agaibh does not make any sense to you, then you are totally unqualified to re-purpose your garage door opener. Seek the services of a licensed electrician before you set something on fire.
Given your statements that (1) the motor turns in one direction only, and (2) that it "got pretty hot" after running for one minute, leads me to believe that this particular motor is either wired wrong by you, or it is unsuitable for use to drive a grain mill, with or without reduction pulleys.
Garage doors go up or down, requiring some mechanism to reverse the direction when fully raised or fully lowered, or when an obstruction is encountered.. This is usually done by reversing the motor direction. If your motor does not run in two directions, it is either wired incorrectly or damaged... maybe both. That may account for why it "got pretty hot" after running for one minute.
Garage door motors are designed for intermittent duty. One does not normally spend endless periods of time opening and closing garage doors. One minute (or less) ON followed by at least a minute of OFF time for motor cooling is reasonable. Running the motor continuously for ten minutes is probably outside the design specifications for that motor.
Here is yet another example of a newbie posting a
solution (re-purpose a motor salvaged from a garage door opener) instead of asking for help to solve a
problem (how do I select a motor to operate my grain mill?). It may turn out that your garage door motor could work fine, although perhaps with a cooling fan attached to its shaft for prolonged operation. But you would need to run the motor under an actual load and measure the temperature rise and the
rate of temperature rise to determine if it is suitable.
somehow I plugged some things here, cut some things there, and now it works
If that's the way you solve electrical problems, you don't need any help from anyone here. Go forth and set the world on fire with your unique paradigm. Or maybe start a career as a plastic surgeon.