Constraint

Any entity that constrains one or more physically simulated entities (such as func_physbox or prop_physics) to each other.

Below is a (so far incomplete and somewhat unconfirmed) list of all contraints:

Basic constraints

• phys_constraint constrains distance and rotation.
• phys_lengthconstraint constrains distance only.
• phys_keepupright constrains rotation only.

Specified constraints

• phys_ballsocket constrains distance to the origin specified.
• phys_hinge constrains distance and rotation to the axis specified.
• phys_slideconstraint constrains movement to the axis specified.

Complex constraints

• phys_pulleyconstraint
• phys_ragdollconstraint
• phys_spring constrains length and rotation like a spring.

• phys_constraintsystem is used to manage a group of interacting constraints and keep them stable.
• info_constraint_anchor used to attach constraints to a local position on an entity. Usually constraints will attach to the center of mass of an object. Attach the desired constraint to this entity, and then parent this entity to the entity you want the constraint to apply to.