Animation Constraints

Animation constraints are used to help automate the animation process. They can be used to control an object’s position, rotation, or scale through a binding relationship with another object.

A constraint requires one object and at least one target object. The target imposes specific limits on the constrained object.

For example, if you want to quickly animate an airplane flying a predefined path, you could use a path constraint to restrict the airplane’s motion to a spline path.

The constraint’s binding relationship with its targets can be animated on or off over a period of time.

Common uses for constraints:

Linking one object to another over a period of time, such as a character’s hand picking up a baseball bat
Linking an object’s position or rotation to one or several objects
Keeping an object’s position between two or more objects
Constraining an object along a path or between multiple paths
Constraining an object along a surface
Making an object point toward another object’s pivot point
Controlling the “look at” direction of a character’s eyes
Keeping an object’s orientation in relation to another

There are seven types of constraints:

Attachment constraint attaches an object’s position to a face on another object
Surface constraint restricts an object’s position along the surface of another object
Path constraint restricts an object’s movement along a path
Position constraint causes the constrained object to follow the position of another object
Link constraint links the constrained object from one object to another
Look-At constraint constrains an object’s orientation so that it’s always looking at another object
Orientation constraint causes the rotation of the constrained object to follow the rotation of another object

Using Constraints with Bones

Constraints can be applied to bones as long as an IK controller is not controlling the bones. If the bones have an assigned IK controller, you can only constrain the root of the hierarchy or chain.