Option 1: Fixed Pulley Centres

FixedPulleys

The centre of each pulley does not move relative to the machine frame [Base-Part]. It is the most common arrangement.

Thus:

The sketch-loop/path is a sketch-llop in the Base-Part.
Each Pulley is a Part that is joined to the Base-Part with a Pin-Joint.

A Pulley Part can be a:

Drive Pulley
The Drive Pulley is kinematically-defined [Green Part-Outline]  before you use Add Pulley.
The DriveR Pulley rotates to move the Belt.

Linear Motion of Belt =

Drive Pulley Radius x Drive Pulley Angular Motion

Driven Pulley
The Driven Pulley is not kinematically-defined [Blue Part-Outline] before you do Add Pulley.
The Driven Pulley is rotated by the Belt. It becomes kinematically when you do Add Pulley.

Angular Motion of Pulley =

Linear Motion of Belt / Pulley Radius.

Pulleys that have 'Fixed-Centres' rotate with their centres fixed to the Base-Part.

It is possible to have:

FixedBelts

When Pulleys have Fixed Centres, the:

Pulleys

Pulleys are Rotating-Parts, with Pin-Joints at the centre-Points of the Arcs in the sketch-loop in the Base-Part
Use the Pulley dialog-box to edit the Number-of-Teeth of each with the

Belt

The 'Belt' is a sketch-loop
When the Pulleys are on fixed-centres, add the sketch-loop to the Base-Part

Motion

The Pulleys or the Belt move with a specified motion.

When the motion is specified for the:

Belt: We use a Motion-Path FB to define the motion of a Motion-Point along the sketch-loop on the Base-Part. Then, the Pulley's motion comes from the Belt's motion.
Pulley. We use a Motion-Dimension FB to define the rotation of the Pulley.  Then, the Belt's motion comes from the Pulley's motion.

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