With constraints, you can drive the position and orientation of one object with the transformation settings of another object. The object that is driven is called the constrained object, and the driver object is called the target object. The specific channels that are driven by a constraint depends on the type of constraint. For example, for an object constrained by a point constraint, only its X, Y, and/or Z translations are driven by its target objects. When a constraint relationship has more than one target object, weights are used to determine the amount of influence each object has on the constrained object. For more information on constraints, see Constraints.
Point constraints limit and control only the translation channels of the constrained object. Point constraints are useful when you want to constrain the position of one object to that of another without parenting. For example, you can use a point constraint to constrain the model of a crate to an animated train model and to the model of a crane that lifts the crate on and off the train. In this example, you can key the targets (the train and the crane) weights to determine which model at what time in the animation controls the translation of the crate. For more information on point constraints, see Point constraints.
Orient constraints limit and control only the rotation channels of the constrained object. Orient constraints are useful when you want to constrain the orientation of one object to that of another. For example, you can use an orient constraint to constrain the blades of one windmill to those of another. In this example, when the target windmill’s blades turn around their axis, the constrained windmill’s blades rotate around their own local axis. For more information on orient constraints, see Orient constraints.
Parent constraints cause the constrained object to inherit the transformations and global orientation of its target objects, mimicking a parent-child relationship. For example, you can constrain the model of a hat to the head and hands of a character with a parent constraint, so that when the head nods and rotates side to side, the hat follows the head’s movements. And when the hand grabs the hat and lifts it off the head, the hat follows the hand. In this example, setting and keying the target weights lets you anchor in time the amount of influence the head and hands have on the hat. For more information on parent constraints, see Parent constraints.
Aim constraints limit and control the rotation channels and aim vector of the constrained object. The aim vector is an attribute on the aim constraint that forces the constrained object to always point at the target objects. Aim constraints are useful when you want the constrained object to always follow and point at the target objects. For example, you can constrain the eyes of a character to track the movements of another character in your scene. For more information on aim constraints, see Aim constraints.
You can apply animation and constraints to the same object. When you keyframe a constrained object or assign a constraint to a keyframed object, a pairBlend node is automatically added to the object. You can set and key the pairBlend node to animate the animation-constraint blend weight. The blend weight determines the amount of influence the animation and constraints have on the constrained object.
For example, you can constrain a ball to the hands of two characters and key the hand weights. When the ball is thrown from one character to another, you can then keyframe the ball’s flight through the air. The process of applying animation and constraints to the same object and then keying the blend weight is called animation-constraint blending. For more information on animation-constraint blending, see Animation-Constraint blending.