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# Example35Cogging Torque of Stepper Motor

General

• The cogging torque of a stepper motor is analyzed.

• The relationship between the rotor angle and the torque is calculated with the motor rotation analysis function.
See [Motor Rotation Analysis] for the detail.

• Please be aware that this is a static analysis. The transient phenomena (dynamic magnetic field) is not analyzed.
The coupled analysis with the external circuit cannot be performed either.
If you want to analyze the transient phenomena or perform the coupled analysis with the external circuit, use the transient analysis (Luvens).

• The torque curve and the magnetic flux density vectors are solved.

• Unless specified in the list below, the default conditions will be applied.

### Analysis Space

 Item Settings Analysis Space 3D Model unit mm

### Analysis Conditions

 Item Settings Solvers Magnetic Field Analysis [Gauss] Analysis Type Static analysis Options Select “Calculate the torque”

Set the Torque Calculation tab as follows.

 Tab Setting Item Settings Torque Calculation Coordinates on Center Axis: X=0, Y=0, Z=0 Vectors of the Axis X=0, Y=0, Z=-1

Set the Mesh Tab as follows.

 Tab Setting Item Settings Mesh Meshing Setup Automatically set the general mesh size: Deselect General mesh size: 3[mm]

### Model

A stator and coils are placed in the air.

A magnet (rotor) is set in the center and its center is the rotation axis of the motor.

No current is flowing in coils.

### Body Attributes and Materials

 Body Number/Type Body Attribute Name Material Name 19/Solid Rotor Mag 12/Solid Shaft SM 14/Solid Stator SM 25/Solid Coil 008_Cu * 26/Solid Coil 008_Cu * 27/Solid Coil 008_Cu * 28/Solid Coil 008_Cu *

* Available from the Material DB

The magnetizing direction of Rotor is set as follows.

 Body Attribute Name Tab Settings Rotor Direction Vector: X=0, Y=-1, Z=0

The material properties are set up as follows:

 Material Name Tab Properties SM Permeability Relative Permeability 3000 Mag Permeability Material Type: Permanent Magnet Magnet Magnetization Strength: 1

No setting.

### Motor Rotation Analysis

 Tab Item Setting Rotation Setting Select the Bodies to Rotate Rotor Shaft Rotation Angles Start angle: 0[deg] Stop angle: 360[deg] Step angle: 30[deg]

• Values for each variable can be set for each rotational angle on the variable setting tab.
The coil current can be set for each rotational angle.

### Results

On the [Model] tab,

click ▼ at the bottom of [Run Mesher/Solver] and click [Motor Rotation Analysis] .

Click [Start Calc] to start the calculation.

The result is output by csv format.

In the figure below, the horizontal coordinate is rotational angle, and the vertical coordinate is torque.

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