Why add a Pulley?

The motion of a Pulley is related to the motion of a Belt.

Either the Pulley moves the Belt or the Belt moves the Pulley.


Only Pulley can move one Belt.

One Belt can move MANY [and ALL] Pulleys

The Pulley has an integer number-of-teeth.

The pitch of the 'teeth' on the Pulley is defined by the belt. See Motion-Path dialog to edit the Belt Tooth Pitch

See Pulley dialog-box to edit the number-of-teeth on the Pulley.

Pulleys and 'Kinematic Properties'.

After you do Add-Pulley, a rotating-part becomes a Pulley.

The Pulley is a:

DriveR-Pulley [or Driving Pulley]: Add a Pulley to a Green rotating-Part. MechDesigner calculates the Linear-Velocity of the Belt from the Angular-Velocity of the Pulley.

or a:

DriveN-Pulley: Add a Pulley to a Blue rotating-Part. MechDesigner calculates the Angular-Velocity of the Pulley from the Linear-Velocity of the Belt.

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 DriveR-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 on 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.
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 or an Added-Part.

Add a sketch-path as a sketch-loop to represent the path of the Belt - made with Lines and Arcs.
Each Arc must have a dimension.


There is only one DriveR-Pulley [Driving-Pulley]. a maximum of one Rotating-Part can be a DriveR-Pulley [Driving-Pulley]

The sketch in the Part for the Driven-Part might need a Line from the centre of the arc, only if the Driven-Pulley is a Rocker [Motion-Part].


DriveR-Pulley [Driving-Pulley] is any Green Rotating-Part in that has a Pin-Joint that is coincident with the

If the Driver-Pulley Part is a Rocker and, thus is driven by a Motion-Dimension , then you may need to:

1.Edit the Part with  the sketch of the Belt
2.Make Coincident the centre-Point3s of an Arc1s-red with the Line that is needed to add the Motion-Dimension.



1.Click Kinematic FB toolbar > Add Motion-Path FB7s .
2.Click a sketch-element that is the sketch-loop of 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 that is joined to the centre-Point of the Arc.
A Rocker or a different kinematically-defined rotating-Part5s.


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

1s-red the Pin-Joint

2s The Motion-Path FB

3s The Radius of the Arc [added to the Arc in the Part-Editor]

4s The kinematically-defined rotating Part - the DriveR-Pulley

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



DriveN-Pulleys rotate with a angular velocity given by the Belt.

Elements in the Mechanism-Editor

1s-red The Pin-Joint

2s The Motion-Path [not shown: there is only one Motion-Path FB for one Belt

3s The Radius of the Arc [added to the Arc in the Part-Editor]

4s The rotating-Part that is a Free-Part - a DriveN-Pulley



Click Kinematic elements toolbar > Add Pulley

1.Click the Pin-Joint at the centre of the Rotating-Part*
2.Click the Motion-Path FB7s that gives the Motion-Point8s that moves along the Arc

The Part-Editor opens to edit the sketch of the Motion-Path:

3.Click the dimension4s for the radius of the Arc

The Part-Editor closes

4.Click the Rotating-Part*5s that has a Pin-Joint6s at the centre-Point of the Arc1s-red
5.Click OK-tiny-11-15 in the Command-Manager

* Rotating Part:

Is a Rocker for a DriveR-Pulley, or
a Free-Part for DriveN-Pulleys, or
the Base-Part if the Pulley is fixed to the Frame.



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 to to have a '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 to 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 [Motion-Path]


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

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd