What is the Pole Count of Two-Phase/Three-Phase Stepper Motors?

First, it's important to understand that parameters like pole count are typically relevant for motors such as AC induction motors and BLDC motors, where the number of pole pairs directly determines their synchronous speed (Speed = 120 × Frequency / Number of Poles). But does a stepper motor "have" this parameter?

For stepper motors, the parameter of primary concern to the user is the Step Angle – the angle the motor rotates for each input pulse. This angle is determined by the number of phases, the number of rotor teeth, and the excitation mode. Therefore, the "pole count" information of a stepper motor is already encapsulated within this final parameter, the "step angle."

Taking the most common two-phase hybrid stepper motor as an example, its structure is representative.

• Stator Pole Count: A standard two-phase hybrid stepper motor has 8 main poles. Each main pole contains multiple small teeth (e.g., 5 teeth). Thus, the total magnetic pole effect of the stator can be viewed as the number of these small teeth.
• Rotor Tooth Count: The rotor has a number of small teeth (e.g., 50 teeth). This "rotor tooth count" is essentially half the number of rotor poles (as each tooth can be considered an N pole, the slot an S pole, with adjacent teeth having opposite polarity).

Step Angle Calculation:

Step Angle = 360° / (Number of Phases × Rotor Tooth Count × Number of Excitation Steps)

Using the most common 1.8° two-phase stepper motor as an example:

Number of Phases = 2

Rotor Tooth Count = 50

In full-step mode (2-phase excitation, equivalent to 200 microsteps on a driver): Step Angle = 360° / (2 × 50 × 2) = 1.8°

In common half-step (4-phase excitation, equivalent to 400 microsteps) or microstepping drive modes, a 0.9° step angle can be achieved.

Therefore, a rotor with 50 teeth corresponds to 100 magnetic poles. For the common 1.8° two-phase hybrid stepper motor, you can consider its rotor to have 100 magnetic poles (50 pole pairs).

The same logic applies to three-phase stepper motors. Consequently, when selecting a two-phase or three-phase stepper motor, the parameters you should focus on are:

1. Step Angle: Determines the motor's resolution (e.g., 1.8°, 0.9°).
2. Number of Phases: Determines the type of drive required (e.g., two-phase, three-phase).
3. Holding Torque: The load capacity of the motor.
4. Current: Determines the output current setting of the drive.

Updated on: 30/10/2025