Mechanism | Add Pulley

<< Click to Display Table of Contents >>

Navigation:  MechDesigner Reference & User Interface > 2: Model-Editor, Mechanism-Editor, Part-Editor > Mechanism-Editor: > Machine elements >

Mechanism | Add Pulley

What is a Pulley

A Pulley is a rotating-Part that is engaged with a Belt.

The angular-motion of a Pulley specifies the linear-motion of a Belt - a Driving-Pulley


The linear-motion of a Belt specifies the angular-motion of a Pulley - a Driven-Pulley

Note: Pattern FB and a Driving Pulley:

When a Motion-Dimension FB specifies the rotation of a Driving-Pulley, and you want to Pattern Solid elements from one link on a chain or lug on a belt to all the links or lugs, you must make changes to the timing of the model so that the Belt rotates fully within one Machine-Cycle.

Add a Gearing FB to the input-connector of the Motion-Dimension FB that is driving the Pulley,

In the Gearing FB, set Gearing Ratio = Belt-Length / Pulley-Circumference.

Then, in one machine cycle, the Belt will move one Belt-Length. and the Pattern elements will be along the complete length of the Belt.

Add Pulley

Add Pulley icon

Machine Elements toolbar : Add Pulley

Menu :

Add menu > Mechanism sub-menu > Add Pulley

Dialog :

Pulley dialog-box

Command-Manager: Add Pulley

Command-Manager: Add Pulley


To add a Driving-Pulley or a Driven-Pulley.

Elements that must be in the model before you can use this command:

a)A Pin-Joint that joins a Part to the center of arc . The arc is one of the sketch-elements of a sketch-path that defines the Belt's Path.

b)ONE Motion-Path FB linked to the sketch-path* as the Belt.

c)A dimension for the radius of the Arc (After Add Pulley, the Number of Teeth and Tooth-Pitch specify the radius of the Arc.

d)A Part joined to the Arc's center-Point with the Pin-Joint - see a).


The sketch-path of a Belt may be closed or open.

The sketch-path should be Arcs and Lines with Tangent constraints.



'Expand' then 'Play'

How to...

Full Video of Add Pulley and Belt

Add sketch-elements

Add Rocker

Add Motion-Path FB

Add a Driving Pulley

Add Driven-Pulley



Physical Design Parameters

We do not use a database to make sure the Belt Tooth-Pitch, Belt-Length, Minimum number of Pulley-Teeth are available in sales literature. You must enter these values.

Length of the Belt

Usually, you want the belt to have an integer number-of-teeth. To edit the Belt-Length, edit the Motion Path FB. In it, you can give a target belt length and select a dimension in the sketch-loop to be a driven dimension. From the Target-Belt Length, and the Tooth-Pitch, you can make the total length of the sketch-loop/belt give an integer number-of-teeth.



Driven-Pulley (also called a Driving-Part)

The Kinematics-Tree adds a Pulley-Rocker Kinematic-Element for each Driven-Pulley you add to the model.

The Pulley-Rocker has a Pin-Joint, a Part, and the Path-Joint


This is a kinematically-defined Part a Rocker or one of two Parts with a Pin-Joint in a Dyad.


Add a sketch-path for the Belt.



Edit the Base-Part (typically) or an Added-Part:

1.Add a sketch-path to represent the Belt -

It should include only Lines and Arcs.

The sketch-path is closed(open) for a closed(open) Belt.

1.Add a dimension to each Arc.

Do not add equal constraint to the Arcs.



A Pulley is linked to a Part that rotates about the Arc's center-Point.

If the rotating-Part is a:

Green Part, you will add a Driving-Pulley

a free Part, you will add a Driven-Pulley.

If the Green Part is a Rocker, you must add a Motion-Dimension FB to define its rotation.

In this case, add a LineRed-14-2 (see image above) with its start-Point that is coincident (or merged) with the center-Point of the Arc.


Add the other Elements.



ONE Motion-Path FB for all of the Pulleys on one Belt.

1.Click Kinematic FB toolbar > Add Motion-Path FBRed-14-7.

2.Click a sketch-element in the sketch-path that represents the Belt.


Driving-Pulleys rotate with an angular-motion that is equal to a Green Part. The linear-motion of the Belt is a function of the angular-motion of the Driving-Pulley.


3.Add a Green PartRed-14-4 that rotates about the center-Point of the Arc.


Driven-Pulleys rotate with an angular-motion that is a function of the linear-motion of the Belt.

3.Add a BLUE PartRed-14-4 that rotates about the center-Point of the Arc.


The prepared elements are a

Red-14-1b Pin-Joint

Red-14-2 Motion-Path FB

Red-14-3 The Radius of each Arc (added to the Arc in the Part-Editor)

Red-14-4 A rotating-Part that is a Green Part or a Blue Part for a Driving-Pulley or a Driven-Pulley, respectively.



Click Kinematic elements toolbar > Add Pulley

1.Click a Pin-Joint at the center of the Rotating Part  

2.Click the Motion-Path FB - the Motion-Point that moves along the Belt

The Part-Editor opens to edit the sketch to which the Motion-Path has been added:

3.Click the dimension that defines the radius of the Arc

The Part-Editor closes

4.Click the rotating-Part* that has a Pin-Joint at the center-Point of the Arc

5.Click OK-tiny-11-15 in the Command-Manager

* If the rotating-Part is a:

a kinematically-defined Part - a Driving-Pulley is added to the model

a Free-Part - a Pulley that will be driven by the Belt is added to the model.



The :

New Pulley element schematic shows in the graphic-area.

The Pulley must have an integer number-of-teeth. The Tooth-Pitch is specified by the Belt in the Motion-Path FB dialog-box

Pulley Pitch-Circle-Diameter (P.C.D.) (defined by the Radius of the Arc) changes so that the Pulley has an integer number-of-teeth.

Radius of the Arc becomes Read-Only in the Part-Editor.

Use the Pulley dialog-box to edit the number-of-teeth.