Fixed Pulleys Centres: Pulleys become driven by a Belt

This design arrangement is a little more unusual than the Belt driven by a Pulley.

Physically, the Belt is wrapped around freely rotating Pulleys. The Belt is driven by a motion-values at the input-connector to the Motion-Path FB.

Free Running Pulleys that are driven by a Belt

Preparation : Add Belt-Path and 'Free' Pulleys.


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

Either Hover+Drag or merge the Points at the end of each Line and Arc to give a sketch-loop.

STEP 3: You MUST dimension each Arc1s-red

The exact radius of the Arc is not important. However, MechDesigner will use the value to find a Pulley with a radius that is near to its radius and has an integer number-of-teeth.

STEP 4: Close the Part-Editor


STEP 5: Click Add Motion-Path FB2s in the Kinematic-FB toolbar

The Command-Manager dialog starts. The selection-box needs you to click a sketch-element.

Click an Arc or a Line in the sketch-loop.

Click OK in the Command-Manager.

The Motion-Point (from the the Motion-Path FB2s) shows at the start-Point of the sketch-element you select in the sketch-loop.

STEP 6: Add a Linear-Motion-Path FB

Connect the Linear-Motion FB to the Motion-Path FB with a wire.

When you connect a Linear Motion FB directly to a Motion-Path FB, the Motion-Point will move along the total length of the sketch-loop for each Machine Cycle.

You can move the Motion-Point with a different motion, with a Motion FB, of course.


STEP 7: Add one Part3s for each Arc

The length of each Part is not important.

STEP 8: Add a Pin-Joint4s between the Point in each Part and the centre-Point of an Arc in the sketch-loop

The Pin-Joint will be the centre of the Pulley rotating shaft.

Note: Usually, join the origin of the Part to the centre-Point of the Arc.

Use 'Add Pulley' command


You need to use Add Pulley for each Pulley.

Click Add Pulley in the:

Mechanism menu

- or -

Kinematic-elements toolbar


Add Pulley opens in the Command-Manager.

[Note: Refer to the images in the 'Preparation' section, above, to identify the four elements].

Click, in the graphic-area, the four elements:

1s-red The Pin-Joint

2s The Motion-Path FB

The Part-Editor opens to show the sketch-loop for the Belt.

3s The Dimension of the Arc sketch-element

The Part-Editor closes.

4s The Part joined with a Pin-Joint1s-red at the centre-Point of the Arc.

Click 'OK' to complete the command

MechDesigner adds the Pulley.

Do Add Pulley again, to add a Pulley to the second Arc and rotating-Part.



The Pulleys are 'Driven-Pulleys'.

This means their angular-velocity is given by the linear-speed of the Motion-Point along the sketch-loop (Belt) and the radius of the Pulley.

When you add a Pulley, the radius of the Arc changes so that there are an integer number-of-teeth on the Pulley.
The Parts are horizontal when the MMA is zero.
Driven Pulleys are Purple
Edit the number-of-teeth with the Edit Pulley dialog.

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