I am planning to purchase a CNC-ready mill from its manufacturer but put the controls together myself separately using various off-the-shelf components. The control system will be based on the Arduino Uno along with a daughter card known as the gShield which can drive three stepper motors. This board contains three TI DRV8818 Stepper Motor Controller IC's, one for each motor. The data sheet states "up to 2.5A per winding" for the driver IC. The stepper motors have many constraints so the number of suitable ones that are in stock are limited. I have found one that is rated at 2.0A and another one that is rated at 2.8A. My instincts tell me that I should select the 2.0A stepper so that it will not exceed the output on the driver. However, some current sources are current-limited so it would be okay to drive a load that is rated at 2.8A because the driver will not exceed the capacity of the load. My worry is that if the driver forces 2.5A into a 2.0A winding then it would threaten the winding on the stepper motor with burn out. Can anyone give me the correct reasoning for matching stepper motor to driver?
The DRV8818 can be current limited to whatever value you choose (within reason) by altering two resistors per motor: -
Look at IsenA and IsenB in the data sheet - top of page 11: -
Either stepper motor should work for you.
Couple of things to note:
1) The DRV driver chip has a current-limit input that is normally connected to a potentiometer. This allows you to set the current limit to a value that matches the motor.
2) The DRV motor driver will NOT deliver the full rated current without heatsinking.
One of the many reasons that I like the DRV carrier boards made by Pololu so much is that they make it easy add a heatsink.