Create a Belt-Pulley Subsystem

In a belt-pulley system, mechanical power is transmitted using a long, flexible belt that wraps around rotating pulleys. This power transfer occurs through friction between the belt and the pulley surface. The belt-pulley subsystem in MotionView enables rapid assembly of such a system with minimal inputs, streamlining the process efficiently.

The belt-pulley system is assembled within a XZ plane of a user defined reference marker, meaning the XZ plane of the marker aligns with the plane formed by the pulley centers. Orienting the reference marker allows you to rotate the belt-pulley system within a global system. Only in instances involving an NLFE belt formulation, is it essential for the reference marker to remain aligned with the global frame.

MotionView offers three types of belt-pulley systems:

Nonlinear Finite Element (NLFE) based – The belt is modeled as a series of connected nonlinear finite element beams. Use this model if you are interested in a high fidelity model that returns accurate belt stresses and strains.
Note: These simulations can take a long time.
Discretized rigid bodies – The belt is modeled as a series of rigid bodies connected by bushings. Use this model if you are interested in the overall motion of the belt-pulley system. These simulations are usually faster than with NLFE or Substructured Flexbodies.
Substructured Flexbodies – This is an experimental feature available in version 2024. The belt is modeled as a series of linear (CMS) flexible bodies connected by fixed joints. This method offers a faster solution compared to NLFE formulation and with a higher fidelity than discretized rigid bodies formulation.


Formulation	NLFE	Discretized Rigid Bodies	Substructured Flexbodies
Speed	Very low	high	medium
Accuracy	high	low	medium

To create a belt-pulley system, follow the steps below:

From the Assembly ribbon, click the Belt/Pulleys icon.
The Add a Belt-Pulley Subsystem dialog is displayed.
Click the System collector and decide which system the belt/pulley needs to be created in.
Specify a variable name and label for the belt/pulley.
By default, variable names of entities in MotionView follow a certain convention. For example, all belt/pulley entities have a variable name starting with bp_. This is the recommended convention to follow when building models in MotionView since it has many advantages in model editing and model manipulation.
Select the type of Belt Formulation to represent the belt using the drop-down menu.
If a reference frame other than global frame is to be used, select the reference marker for pulley coordinates by double-clicking on the Marker collector (located in the lower, left of the dialog).
The belt-pulley system will be created such that the assembly lies within the XZ plane of the reference frame.
By default, two pulleys are available. To add or delete a pulley, use the right-click option on a row item indicating the pulley number.
Enter values for the X and Z coordinates of the pulley center in the reference marker coordinate frame.
Enter a value for the radius of the belt and specify which side (inner or outer) of the belt loop the pulley is positioned from the drop-down menu.
Specify the total number of pulleys to create.
As the pulley is added/deleted, this field will be automatically updated.
Enter values for the belt width and belt thickness in the text boxes on the right side of the dialog.
A linear elastic Belt Rubber material is available in MotionView and is selected by default. To use a different material, double click on the MaterialProperty collector and select a different material from the list.
To create an NLFE belt formulation, complete the steps below:
1. In the NLFE Belt Component area, the minimum number of NLFE beam elements required to accurately represent the belt based on the calculated belt profile is displayed in blue. By default, the minimum number of required elements is used. To use more elements, deactivate the Use minimum required option and specify the number of NLFE beam elements to be created.
2. The effective diameter based on the calculated profile length of the belt in the installed position is also displayed in blue. By default, the dialog sets a value for the free diameter by a known amount of offset from the installed free diameter. Deactivate the Use calculated value option to provide a different value for the belt free diameter.
  
  Note: This number should be smaller than the installed belt diameter, so that the belt is sufficiently pre-tensioned. The greater the difference between the free diameter and the Installed diameter, the more pretension is induced.
To create a Discretized rigid bodies belt formulation, complete these steps:
1. In the Belt Stiffness Properties section of the dialog, enter tensile stiffness and tensile damping values along the longitudinal direction of the belt.
2. Enter bending stiffness and bending damping values along the bending direction of the belt.
3. Enter a value for the pre-tension of the belt.
4. For the Belt Contact Properties (Impact) section, the parameters are the same as that found in the Contact panel with Impact method. Refer to the Contacts tool topic to learn more about each of the parameters.
To create a Substructured Flex Bodies belt formulation, complete these steps:
1. Enter a value for the Belt Preload (in force units).
2. For the Belt Contact Properties (Impact) section, the parameters are the same as that found in the Contact panel with Impact method. Refer to the Contacts tool topic to learn more about each of the parameters.

Once all the above information is entered, click OK to create the belt-pulley system and exit the dialog.

Note: In the case of Substructured Flex Bodies, the flex body (CMS) is automatically created in the background for the belt segment.

The NLFE belt-pulley system that is created has the following architecture:


Entity	Description
Bodies	Rigid pulley bodies and an NLFE belt body consisting of a series of nonlinear beam finite elements.
DataSet	A dataset where all editable values are stored. After the creation of the belt-pulley system, you can change the free diameter and width of the belt through this dataset.
Points	The points that define the uninstalled belt profile and the pulley centers. These are hidden by default.
Graphics	The graphics for the pulleys.
Joints	Revolute joints between the pulley and attaching body. In addition, there are joints that connect the pulley and belt body that help in transmitting motion.
Markers	A reference marker to define the uninstalled configuration of the belt (hidden by default).
Templates	Includes NLFE statements that are currently not supported by MotionView. These include GRIDS at the periphery of the pulley, LINE2 elements that model contact between belt GRID and pulley GRID, and CONN1 elements that restrain the belt with the pulley along normal of the belt-pulley plane.

The discretized rigid bodies belt-pulley has the following architecture:


Entity	Description
Bodies	Rigid pulley bodies and a belt body consisting of a series of connected rigid bodies is created.
DataSet	A dataset where all editable values are stored. After the creation of the belt-pulley system, you can change the free diameter and width of the belt through this dataset.
Points	The points that define the belt profile and the pulley centers. These are hidden by default.
Graphics	The graphics for the pulleys and belt.
Joints	Revolute joints between pulley and attaching body. In addition there are joints that connect the pulley and belt that hold the belt in the system plane.
Markers	A reference marker to define the uninstalled configuration of the belt (hidden by default).
Templates	Includes MotionSolve command statements to hide the graphics used in contact.

The Substructured Flex Bodies belt-pulley has the following architecture:


Entity	Description
Bodies	Rigid pulley bodies and a belt body consisting of a series of connected rigid bodies is created.
DataSet	A dataset for contact properties.
Points	The points that define the belt profile and the pulley centers. These are hidden by default.
Deformable Curve	A deformable curve running through markers on the flexible bodies at the belt profile points.
Graphics	The graphics for the pulleys.
Joints	Revolute joints between pulley and attaching body. Fixed joints between belt flexible bodies. In addition, there are joints that connect the pulley and belt that hold the belt in the system plane.
Markers	A reference marker to define the uninstalled configuration of the belt (hidden by default). Markers on flexible bodies used in Deformable Curve.
Solver Arrays	Solver arrays that list the modal IC arrays for the flexible bodies.
Templates	MotionSolve statements set the modal IC arrays on the flexbodies and Deformable Curve contact definition.

Tip:

Select Show additional parameters to specify variable names and labels for the points that are to be created.
As the pulley X, Z, radii, and the belt side parameters are set, the preview image shows the belt-pulley system configuration. The line joining the pulleys tangentially represents the belt. For any incompatible information (for example, overlapping locations of the pulleys, distance between two pulley centers smaller than the summation of their radii) the belt line will not be visible. Cross belt and out of plane pulley configurations are not supported.
To return to default settings, click Reset to Defaults.

Edit a Belt-Pulley System

Change the Pulley Mount Bodies

The pulleys, by default, are connected to ground body via revolute joints. To change any of these attachments to a different body, select the BeltPulley system in the Model Browser and change the pulley_body_n Body attachment in the Attachments section of the Entity Editor, as shown below:

Change the Belt Material (for NLFE belt and Discretized rigid bodies only)

To change the material of the belt (for NLFE belt and Discretized rigid bodies only), select the BeltPulley system in the Model Browser and change the MaterialProperty attachment (Belt Graphic Material) to the belt-pulley system in the Attachments section of the Entity Editor:

Note: Belt material cannot be changed for Substructured Flex Bodies based formulation after the system is created.

Change the Pulley Material

The pulley material can be changed by:

For NLFE Belt and Discretized rigid bodies, select the graphic system of the pulley and change the material attachment in the Attachments section of the Entity Editor:
Figure 3.
For Substructured Flex Bodies select the Pulley graphic in the Model Browser and change the Material under the Properties section of the Entity Editor:
Figure 4.

Change the Belt Parameters (for NLFE belt and Discretized rigid bodies only)

Belt parameters can be changed through the dataset Parameters DataSet available within the belt-pulley system.

The parameters that are active can be changed, while those that cannot be changed are grayed out.

Note: Belt parameters cannot be changed for Substructured Flex Bodies based formulation after the system is created.

Change Stiffness Parameters for Discretized Rigid Bodies

In the case of a discretized rigid bodies belt, the stiffness parameter and belt tension can be changed using the dataset Parameters Stiffness DataSet:

Change Contact Parameters for Discretized Rigid Bodies and Substructured Flex Bodies

In the case of a discretized rigid bodies or Substructured Flex Bodies belt, the parameters for contact between the belt and the pulleys can be changed through the dataset Parameters Contact DataSet and ds_contact respectively.