Using Traction and Belts for Layout Sketches
The Traction 
relation
and the Belt/Chain 
tool (Blocks toolbar) enable you to use layout sketches to
create these mechanisms:
Multiple gear sets
Cable and belt pulleys
Chain sprocket systems
Traction
The Traction relation creates
relative rotation constraints between sketch entities by adding a tangent
relation between blocks that represent pulleys or sprockets.
To add traction relation:
Sketch multiple circular or linear entities to
represent gears, rack and pinion mechanisms, etc.
Make each entity a separate block.
Add relations and dimensions to eliminate motion
not related to the mechanism.
Limit the use of the Fix relation, for example to the center
of one circle. Use horizontal and vertical relations, dimensions, or construction
geometry to locate the centers of additional circles or sketch entities.
Adding multiple fix relations potentially restricts the model's degrees
of freedom.
In the graphics area, select two sketch entities
to which you want to add relative rotation constraints.
Belt/Chain Tool
To use the belt chain tool:
Sketch multiple circular entities to represent
belt members.
Although not required, making
each entity a block is recommended.
Click Belt/Chain
(Blocks toolbar) or Tools,
Sketch Entities, Belt/Chain.
Add relations and dimensions to eliminate motion
not related to the mechanism.
Add belt
members and belt to create the mechanism.
