Use Assign Controller to assign animation controllers to any animatable parameter or track in Track View.
Animation controllers and constraints provide powerful tools for animating all the objects and materials in a scene. For example, rather than keyframing the position of an object in your scene, the object can follow a spline using the Path constraint, react to any animated parameter using a Reaction controller, or move to the beat of music using the Audio controller. You can combine controllers with a List Controller. You can drive a single vertex or control point on a complex object by a variety of controllers.
You can also assign controllers using the right-click menu in the Track View Controller window. Or you can assign controllers on the Motion panel, with Schematic View, and from the Animation menu.
To view lists of available controllers and constraints, see Animation Controllers and Animation Constraints.
Technically, there is no difference between a controller and a constraint. A constraint is simply a controller that requires the use of a second object. For example, a Path constraint is a controller that requires a spline object for a path.
Special-case controllers are not assigned manually with the Assign Controller command. They are applied automatically during certain procedures.
Barycentric Morph Controller is applied by selecting an object and clicking Command panel Geometry Compound Objects Morph.
A Master Point Controller is assigned when animating vertices, control points, or vectors in the sub-object mode of an Editable Mesh, Editable Spline, Editable Patch, NURBS surface, or FFD modifier.
Slave Controllers can be assigned manually, but is also automatically applied to selected tracks when a Block controller is created in Track View Global Tracks. A Slave controller transfers key data to a Block controller. Slave controllers are described in the Block controller topic.
To assign an animation controller in Track View:
If a parameter has already been animated, then assigning a new controller has one of the following effects: