Which motor is right for your cnc application?

Stepper motors generally are not available in frame sizes larger than NEMA 34, with most applications falling in the NEMA 17 or NEMA 23 motor sizes. As a result, it is unusual to find stepper motors capable of producing more than 1000 to 2000 ounce inches of torque.

Adding an encoder will enable the system to accurately track movement, but it will not be able to overcome the basic physics of the motor. For applications requiring improved positioning accuracy and resolution, servo motors provide a better solution.

Servo Motors
Like stepper motors, servo motors have many implementations. Let’s consider the most common design, which incorporates a rotor with permanent magnets and a stationary stator with the windings. Here too, the current creates a magnetic field distribution that acts on the rotor to develop torque. Servo motors have significantly lower pole counts than stepper motors, however. As a result, they must be run closed-loop.

Final ThoughtsServo motors offer an undeniable performance advantage. In terms of repeatability, however, stepper motors can be quite competitive. This point brings up a common misconception about stepper motors, which is the myth of lost motion. As we discussed previously, the mass-spring nature of a stepper motor may result in a few lost steps. Because the drive is commanding the stepper to move to an angular location, lost steps are not carried over from rotation to rotation, however. Rotation to rotation, stepper motors are highly repeatable. Look for a more detailed discussion of this topic in a future blog post.

When your application is forgiving but your budget is not, consider a stepper motor. If performance is the most important aspect, a servo motor will do the job but be prepared to pay more.

Design Tips for Using Step Motors
Some Basic Knowledge among Nema17, NEMA 23 and NEMA 24 motor