, 
, and 
.
A coupler can be used to relate relative coordinates of revolute, translational, and cylindrical joints. The relative coordinates may have a linear relationship, which is defined as scales. Couplers are useful if user’s model uses belts and pulleys or chains and sprockets to transfer motion and energy. Although the user can couple only two or three joints, more than one coupler can come from the same joint. If the user can only create a two-joint coupler, the user selects the driver joint, the joint to which the second joint is coupled, and the coupled joint, the joint that follows the driver joint. To specify the relationship between the driver and the coupled joint or to create a three-joint coupler, the user modifies the coupler.
As an example, the following constraint equation is generated
in RecurDyn when the scales are defined as , , and .
Figure 1 Coupler icon on Working Window
Figure 2 Coupler icon of the Joint group in the Professional tab