How to Choose
vs. Servo Motors
Choosing the right motor involves considering load size,
speed, torque requirements, and resolution
By Matthew Tellier, Product Manager, Motion Control Advanced Micro Controls, Inc.
The basic difference between a stepper and a servo
motion control system is the type of motor and how it
is controlled. Stepper and servo motors have multiple
magnetic poles energized by either a permanent magnet, or
by feeding current through the coils of a winding.
Stepper motors are electric motors without commutators,
a type of multipole brushless DC electric motor that divides
a full rotation, typically into 50 to 100 equal steps. The
motor’s position can be commanded to move and hold at
any one of these steps without the need for a feedback
sensor, such as an encoder. Although stepper motors can
accurately move among their many poles incrementally, an
encoder can be added for more precise positioning.
Typical servo motors have 4 to 12 poles, and with so few
poles need feedback to keep track of their position. A servo
motor is coupled with an encoder and a sophisticated
controller, allowing for control of angular or linear position,
For many motion control applications, designers and engineers can choose between a
servo or stepper motion control system.
Much of this decision is driven by the
motor, although the controller and the
drive also play into the evaluation. Making
the correct selection has long-term benefits
that positively impact production efficiency
and overall life cycle cost, while making the
wrong choice can lead to performance and
This IDEC PLC comes with embedded motion control macro instructions, allowing
users to quickly and simply implement single- and multi-axis stepper motion control
(photo courtesy of IDEC).