What is a Pulley

To define the motion of rotating Parts as Pulleys connected with a Belt

There are two kinematic-pulleys:

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

Add Pulley

Add Pulley icon

Kinematic Elements Toolbar : Add Pulley (<<left of graphics-area)

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 Pin-Joint that joins a Part to the centre of arc . The arc is one one of the sketch-elements of a sketch-path that defines the Belt's Path.
A Motion-Path FB linked to the sketch-path. This gives a Motion-Point on the sketch-path.
A dimension that defines the Radius of an Arc, that will becomes the Radius of the Pulley. (After Add Pulley, the Number of Teeth and Tooth-Pitch specify the Radius of the Arc
A Part, that is joined with the Pin-Joint( element 1) to the centre-Point of each Arc

Note: The sketch-path of a Belt may be closed or open. It is usually closed.




Edit the Base-Part (typically) or an Added-Part (if the pulleys and the Belt move with a Part).

Add a sketch-path to represent the path of the Belt - made with Lines and Arcs.

The sketch-path is most typically a sketch-loop, as you will want to add a closed belt. However, the belt might be and open belt.

Each Arc must have a dimension.



A Pulley is linked to a Part that rotates around the centre of the Arc.

Before you add the Pulley, if the Part is a:

kinematically-defined Part, it will be a Driving-Pulley.
a free Part, it will be a Driven-Pulley.

The kinematically-defined Part may be a Rocker (Motion-Part) (see Note 1), or a rotating Part whose motion is specified by its joints to other Parts.

Note 1: If the kinematically-defined Part and Driving-Pulley is a crank/Rocker, you will need to add a Motion-Dimension FB to define its rotation. In that case, you will need to:

1.Add a LineRed-14-2 with its start-Point coincident or merged with the centre-Point of the Arc



1.Click Kinematic FB toolbar > Add Motion-Path FBRed-14-7.
2.Click a sketch-element in the sketch-path that is to become the Belt.

A Motion-Point is now at the start-Point of the sketch-element.

DRIVER-PULLEY PART (also called a Driving Pulley)

3.Add a rotating Part with a Pin-Joint at the centre-Point of the Arc.
A Rocker or a different kinematically-defined rotating-PartRed-14-5.


The prepared model for a Driving Pulley is to the left. The four elements are:

Red-14-1b The Pin-Joint

Red-14-2 The Motion-Path FB

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

Red-14-4 The kinematically-defined rotating Part - will be the Driving-Pulley

The rotational motion of the Driving-Pulley gives the velocity to the Motion-Point(s) along the sketch-loop.



Driven-Pulleys rotate with an angular velocity given by the Belt.

Elements in the Mechanism-Editor

Red-14-1b The Pin-Joint

Red-14-2 The Motion-Path (not shown: there is only one Motion-Path FB for one Belt

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

Red-14-4 The rotating-Part that is a Free-Part - will be the Driven-Pulley



Click Kinematic elements toolbar > Add Pulley

1.Click a Pin-Joint at the centre 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 centre-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.



'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.

Minimum Number-of-Teeth on a Pulley

You must make sure the Number-of-Teeth parameter in each Pulley > minimum practical number-of-teeth. Typically, the minimum number-of-teeth is ~10 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.

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd