Home / Examples / Magnetic Analysis (Gauss, Static Analysis/Harmonic analysis) / Example 35: Cogging Torque of Stepper Motor

Example 35: Cogging 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 using 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.

Results will vary depending on Femtet version and the PC environment.

Analysis Space

Item	Settings
Analysis Space	3D
Model Unit	mm

Analysis Conditions

Item	Settings
Solver	Magnetic Analysis [Gauss]
Analysis Type	Static Analysis
Options	Select [Torque Calculation].

Set the Torque Calculation tab as follows.

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

Set the Mesh Tab as follows.

Tab

Setting Item

Settings

Mesh

Meshing Setup

Set the general mesh size automatically: 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
Mag	Magnet	Magnetization Strength: 1

Boundary Conditions

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 the individual rotational angle on the variable setting tab.
The electric current flowing through the coil can be changed at the different rotational angles.

Results

Use the motor rotation analysis dialog box. Once the modeling is done,

go to on the [Model] tab and click ▼ at the bottom of [Run Mesher/Solver] . Then click [Motor Rotation Analysis] . Then the dialog box appears.

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.