The Damping for Physics Constraints work a bit differently than with Physics Bodies: they only work on Limited Motions and when a motion attempts to go beyond its limit. Setting a
Physics Constraint's Motion(s) to Limited will display the Soft Limits:
The two Angular Swing Motions share Damping values, the Angular Twist receives its own Damping values, and all the Linear axes use the same Damping values. While they may have
separate properties, the properties all have the same effect on the Motions they relate to.
When a limit is exceeded, this value affects how harshly the constraint attempts to stop the offending motion. The default of 50 will barely affect the motion, a value of 5000 will appear to bounce back into limit, and 50000 will completely deflect the motion.
Like the Damping on Physics Bodies, this defines how much the motion should be slowed. Unlike Damping on Physics Bodies, the damping affect occurs only when the Motion Limit is exceeded, draining momentum until the Physics Body stops.
The two values work together to create different effects. A high Stiffness and low Damping will look like a hard limit, while having them both high will appear to be move through
tar, coming to a stop gently but quickly. A good deal of experimentation is necessary to find the right values for your specific needs.
For more information on Constraints, see: PhysX Constraint User Guide
Or for a reference on the properties available to Physics Constraints,
see: Physics Constraint Reference