Fixed Centre Pulleys

We will add a Multi-Pulley and Belt system.

We will define the motion of one Pulley and MechDesigner will find the angular motion of other Pulleys.

We will edit the Number of Teeth on each Pulley

We will edit the Length of the Belt with Controlling Dimension, using the Target Belt Length parameter.



STEP 1: Edit the Base-Part
STEP 2: Add a closed sketch-chain (sketch-loop) to represent the Path of the Belt

We will add a Line, and then we can add a Rocker in the Mechanism-Editor.

STEP 3: Add a Line Red-14-1b - its start-Point is merged or coincident with the centre-point of an Arc.
STEP 4: You MUST add a dimension to each Arc

The exact radius of the Arc is not important.

STEP 5: Close the Part-Editor


STEP 6: Add Motion-Path FBRed-14-2

Select the sketch-loop that represents the path of the belt.

The Motion-PointRed-14-3 shows at the start-Point of the sketch-element you select in the sketch-loop.


STEP 7: Add a Part for each Pulley.

Add one Part near to the centre-Point of each Arc

STEP 8: Add a Pin-Joint between the centre-Point of each Arc and the start-Point of each Part

There is one rotating Part (that is, a Part + Pin-Joint) for each Pulley.

The length of each Part is not important.


STEP 9: Add a Motion-Dimension FB to the PartRed-14-4 you wish to be the Driving Pulley.

A maximum of one kinematically-defined Part can be a Driving Pulley.

Use Add Pulley

You must do Add Pulley for each Pulley


Add menu > Mechanism sub-menu > Add Pulley

- or -

Kinematic-elements toolbar > Add Pulley


The Add Pulley dialog starts in the Command-Manager.

Do Add Pulley to the kinematically-defined Part first.

Click, in the graphic-area, from top to bottom.

1.The Pin-Joint
2.The Motion-Path FB

The Part-Editor opens with sketch-path to which you add the Motion-Path FB

3.The radius Dimension of the Arc

The Part-Editor closes

4.The Part joined with a Pin-Joint at the centre of the Arc.


MechDesigner adds the Pulley.

Do Add Pulley again four more times to add a total of five Pulleys.


Default colours of the Pulleys:

Driving Pulleys are Cyan

Driven Pulley are Magenta

The radius of each Arc changes to give an integer Number-of-Teeth.
Edit the Number-of-Teeth with the Edit Pulley dialog.

Use Edit Pulley dialog box


Edit the Number-of-Teeth on a Pulley.

1.Open the Pulley dialog-box

Double-click a Pulley in the graphic-area

- or -

See How to open a dialog-box


In the Pulley dialog-box

2.Edit the Number-of-Teeth

Repeat 1 and 2 for each Pulley.


3.Edit the Motion-Dimension FB to 0º .

When the Driving-Pulley is at 0º, the other Pulleys will also be at 0º.

Edit the Length of the Belt

Belts have an integer number-of-teeth. Also, belt manufacturers have preferred lengths of belts. We use the Motion-Path dialog-box to enter a Target Path Length

The Target Belt Length tool moves a pulley, or another controlling-dimension, to edit the length of the belt.

Thus, we need a dimension in the sketch-path that will change the length of the belt. We will edit the length of the Belt to an length that is exactly divisible by Tooth-Pitch to give an integer number of teeth on the Belt.

GA-AddPulley-Adjust Path Length-01

In the design to the left, we will make the Tensioning Pulley the pulley at the top the sketch-path.

Therefore, we will use the dimension highlighted in RED. (164.89)

This dimension is the Controlling Dimension.

MechDesigner adjusts this dimension as we edit the Target Path Length

GA-AddPulley-Adjust Path Length-02a

STEP 1: Edit the Motion Path FB to edit the Length of the Belt.
1.Double-click the Motion-Path FB  to open its dialog-box dialog box (or see How to open a dialog-box)
2.Motion-Path dialog-box > Length Control tab > Belt-Tooth Pitch  > Belt Tooth Pitch =5 (mm)
3.Motion-Path dialog-box > Length Control tab > Path Length using Dimension 

You will see the Actual Path Length = 1228.9mm  It is Read-Only.

4.Click the Controlling Dimension box

The Part-Editor opens to edit the Part in which the belt is defined by the sketch-path.

5.Click the dimension you want to use to change the length Belt - see image above

The Part-Editor closes

The dimension value shows in the Controlling Dimension box

The default Target Path Length = Actual Path Length

The Maximum and Minimum Dimension Values are Soft-Limits to the Controlling-Dimension.

You can edit the Maximum and Minimum Values if you need to edit the Controlling Dimension by more.

8.Edit the Target Path Length SLOWLY with the Spin-Box tool to increase or decrease the Actual Belt Length.

If needed, you can select a different dimension to adjust.

1.Click the Clear Controlling Dimension button, immediately below Path Length using Dimension

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