Fixed Pulley centers : the center of each pulley does not move relative to the machine frame (Base-Part). It is the most common belt and pulley arrangement.

Thus:

•The sketch-loop/path is a sketch-loop 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:

•Driving Pulley
The Driving Pulley is kinematically-defined (Green Part-Outline)  before you use Add Pulley.
The Driving 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-centers' rotate with their centers fixed to the Base-Part.

It is possible to have:

1.Pulleys that are driven by the Linear Motion of a Belt

2.Belt that is driven by the Angular Motion of a Pulley

3.Many pulleys with One Belt

4.Two or more Pulleys on one shaft axis (more than one Belt)

Pulleys and Fixed centers:

Pulleys

•Pulleys are Rotating-Parts, with Pin-Joints at the center-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

Belt

•The Belt is a sketch-loop

•When the Pulleys are on fixed-centers, 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. The Pulley PArt is a kinematically-defined Part - for example, we can add a Motion-Dimension FB to define the rotation of the Pulley directly.  Then, the Belt's motion comes from the Pulley's motion.