Fixed Pulley Centers: Belt becomes driven by a Driving Pulley

This design arrangement is very common : there is one Driven Pulley.

The belt becomes driven by the Driven-Pulley. The other Pulleys become driven, via the Belt.

Preparation: Sketch-Loop and the Pulleys



STEP 1: Edit the Base-Part
STEP 2: Add a sketch-loop to represent the path of the Belt

In this example, the sketch-loop has two Arcs and two Lines.

STEP 3: Add a LineRed-14-1b and merge the start-Point with centre-point of the Arc.

It is easier to Add the Arc, then Hover+Drag the Line to merge it with the centre of the Arc.

STEP 4: You MUST dimension each ArcRed-14-2

The exact radius of the Arc is not important. MechDesigner will add a Pulley with an integer number-of-teeth and pitch to give radius that is near to the dimension. You can edit the number-of-teeth and tooth pitch later, of course.

STEP 5: Close the Part-Editor


STEP 6: Add a Motion-Path FBRed-14-3

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

The Motion-PointRed-14-4 shows at the start-Point of the sketch-element you select in the sketch-loop.


STEP 7: Add one PartRed-14-5 for each Arc

The length of the Parts is not important.

STEP 8: Add a Pin-JointRed-14-6 between a Point in each Part and the centre-Point of an Arc.

Usually, use the origin of each Part for the Pin-Joint.

STEP 9: Add a Motion-Dimension FBRed-14-7 to the Part you wish to be the Driving Pulley.

This one way to give a Green rotating-PartRed-14-5 that will be the Driving Pulley. In this case, it is a Rocker.

Use Add Pulley


You must do Add Pulley for each Pulley.


Add menu > Mechanism sub-menu > Add Pulley

- or -

Kinematic-elements toolbar > Add Pulley


Add Pulley opens in the Command-Manager.

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

See Preparation for each element

Red-14-6 The Pin-Joint

Red-14-3 The Motion-Path FB

The Part-Editor opens to show the sketch-loop to which you added the Motion-Path FB.

Red-14-2 The Dimension of the Arc sketch-element with the Green rotating-Part (the left Arc)

The Part-Editor closes.

Red-14-5 The Part joined with a Pin-Joint at the centre of the Arc.

Click OK-tiny-11-15 to complete the command.


MechDesigner adds a Driving-Pulley.

Do Add Pulley again, to add a Pulley to the right-hand Arc and Part.


A Driving-PulleyRed-14-5 is driven by the kinematically-driven Part (the Rocker, in this case).

Drive Pulleys are Cyan
Belt Speed = Radius of Drive-Pulley * Angular-Velocity of the Drive-Pulley

A Driven-PulleyRed-14-6 is added to the free-Part

Edit each Pulley : Number-of-Teeth in the Edit Pulley dialog.


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