The controller is the device that takes signals from the computer and sends them to the stepper motors to create movement of the particular machine axis.
It's hard to see
in the photo but the small package in front has several resistors for
adjusting max motor current and idle current. The board is made
so that they require no soldering.
I am waiting for
parts before I wire up the motors. The motors from Automation
Direct came with connectors already attached. You can buy their
extension cables with the mating connector for $9.00 each, which seems
a little pricey to me. So I planned on cutting them off and
wiring straight in or coming up with a more common connector. The other
night I saw a Molex part number on one of them. After a brief
Internet search I was able to order the mating parts for about $3.00
total plus shipping. I ordered some roller micro switches while I
was there to help balance out the shipping cost.