Motor Controller:
A4983 Stepper Motor Driver Carrier with Voltage Regulators
Power supply:
AC/DC Power Supply Single- Output 7.5 Volt 20A 150W
20amp power supply because I will be running a few other things at the same time.
The minute hand will rotate 359 degrees and then rotate back to 0 degrees every hour.
4oz at 24" would need 96oz torque for the motor. On paper at least.
I'd like to use a stronger motor, but the stronger they are, they begin to exceed the 2amp limit on the controller board. (which at $20 is affordable) Plus in real world conditions I'm not sure if this is overkill? (or underkill?)
Any advice on the proper motor, controller, and power supply combination would be very welcome.
Since the minute hand only needs to move at .016 RPM, you could use a small stepper, run it at a few RPM, and gear the bleep out of it to get lots of torque.
The motor needs about 5V, but the motor controller will need a little (maybe a lot) more, depending on its design.
Bipolar chips like the L293 or L298 need about 2.5V more than the motor, because of the drop across their Darlington transistors. But, because they waste so much energy (about a third of the total, in this case), you'll almost certainly be better off shopping for a controller based on FETs. The datasheet of the controller will tell you what the voltage drop across the drivers is, so you can calculate how much "extra" it needs to give the motor its 5V.
I'm also using the 4983 driver on a Pololu board to control a 6 volt stepper. The 4983 has FET outputs. It requires voltages between 8 - 35 volts applied to the 'VMOT' pin. The Pololu board has a current limit adjustment, so that you can drive the motor with a higher voltage than specified, and it will actively limit the current. I would suggest you apply about 10 volts to the 'VMOT' pin of the Pololu board, then follow the Pololu procedure to adjust the current (you need a meter). Steppers only have current applied to one phase at a time, so the current per phase is the max current the stepper requires. In your case that's 2 amps, the upper limit of the 4983. You get the voltage by multiplying the current by the resistance V = I x R = 5.2 volts. But double it if you're using a 4983, and then limit the current to 2 Amps. So you need a 10 volt 2 amp supply for that stepper.