Instructions for Selecting a Stepper Motor

The Basics of Selecting a Stepper Motor

The vast majority of stepper applications are fairly simple in terms of selecting the motor and drive.  Most applications have one or more of a few criteria, usually including torque, speed, mounting dimensions, and voltage.

For most applications, look for the following stepper motor data:

1. Torque – look at rated holding torque and performance curve
2. Current – look at rated RMS current per phase (match with drive)
3. Inductance – look at line-to-line phase inductance (match with drive)
4. Speed – look at performance curve based on voltage
5. Mounting dimensions – look at catalog drawings
6. Other motor options, such as shaft seal, connectors, rear shaft, etc.

Rated Current:

Select a motor with a rated RMS current that is less than or equal to the current capability of the stepper drive that will be used.  Current produces torque.  If the drive can’t deliver the full rated current of the motor, then the motor will produce less than the rated torque.  There is no problem with this as long as the motor produces the required torque for the application.

Motor Inductance:

Select a motor with winding inductance that falls within the allowable inductance range of the drive that will be used.  If the motor inductance is less than the drive’s minimum inductance, then the output stage of the drive will overheat and fail.  If the motor inductance is greater than the drive’s inductance range, then the motor will have less than optimal performance.

Mounting dimensions:

Keep in mind that most modern motors with NEMA size specifications do not have the standard NEMA size shaft diameter.  Most of the newer motors use a larger shaft because they produce more torque.