Animation menu > Constraints > Path Constraint
Select the object to be constrained > Motion Panel > Assign Controller Rollout > click Position track > click Assign Controller icon > Path Constraint
A path constraint restricts an object's movement along a spline or at an averaged distance between multiple splines.
A path target can be any type of spline. The spline curve (target) defines a path of motion for the constrained object. Targets can be animated using any of the standard translation, rotation, scale tools. Setting keys on the pathÆs sub object level, such as vertex, or segment will animate the path while affecting the constrained object.
A constrained object can be influenced by several target objects. When using multiple targets, each target has a weight value that defines the degree by which it influences the constrained object, relative to other targets.
Using Weight is meaningful (and available) only with multiple targets. A value of 0 means the target has no influence. Any value greater than 0 causes the target to influence the constrained object relative to other targets' Weight settings. For example, a target with a Weight value of 80 will have twice the influence of a target with a Weight value of 40.
Procedures
To assign a Path constraint:
Select a single object.
Choose Animation menu > Constraints > Path Constraint.
You are now in select target mode.
In the viewport, select a shape object.
If a shape does not exist, you can create one from the Create panel > Shapes.
To access the Path constraintÆs parameters through the Motion panel:
Select the path-constrained object.
Click the Motion Panel tab on the Command panel.
In the PRS Parameters rollout, click the Position button.
The Path constraint's settings are located in the Path Parameters rollout.
To assign a Path constraint through the Motion panel:
Select a single object.
Click Parameters in the Motion panel.
Select the Position controller in the Assign Controller rollout.
Click Assign Controller.
Choose Path Constraint from the Assign Position Controller dialog.
Click Parameters in the Motion panel.
Click Pick Path in the Path Parameters rollout.
In the Viewport, select a shape object.
You can create a shape in Create panel > Shapes if one does not exist.
To edit weight values:
Select the constrained object.
Open the Path Parameters rollout in the Motion panel.
Click a target from the list.
Adjust the Weight spinner or enter a numerical value for the weight value.
To animate weight values:
Select the constrained object.
Open the Path Parameters rollout in the Motion panel.
Click a target from the list.
Turn on the Animate button.
Adjust the Weight spinner or enter a numerical value for the weight value.
Interface
Once you assign a Path constraint, you can access its properties via the Path Parameters rollout in the Motion panel. In this rollout you can add or delete targets, assign weighting, and animate each target's weight value.
Note: When you assign a Path constraint via the Animation menu, the software assigns a Position List controller to your object. In the Position List rollout list you will find Path Constraint. This is the actual path constraint controller. To view the Path Parameters rollout with the constraint settings, double-click Path Constraint in the list.
Add Path: Adds a new spline path that influences the constrained object.
Delete path: Removes a path from the target list. Once removing the path target, it will no longer influence the constrained object
Weight: Assigns and animate weight values for each target.
% Along Path: Sets the percent that the object is positioned along the path. This duplicates the Value spinner in the track Properties dialog for the Percent track in Track View. If you want to set keys to place an object at a certain percent along the path, turn on Animate, move to the frame where you want the key set, and adjust the % Along Path spinner to move the object.
Follow: Aligns the object to the trajectory as it follows the contour.
Bank: Allows the object to bank (roll) as it negotiates the curves of the spline.
Bank Amount: Adjusts the amount of the banking to one side or the other, depending on whether the value is positive or negative.
Smoothness: Controls how rapidly the roll angle changes as the object moves through bends in the trajectory. Smaller values will make the object more responsive to subtle changes in the curve, while larger values smooth out jerking. The default value is a good value for general damping along the curve. Values below 2 tend to make the action jerky, but values around 3 can be very useful for simulating a certain degree of realistic instability.
Allow Upside Down: Turn on to avoid the situation in which an object flips when going around a vertically oriented path.
Constant Velocity: Provides a constant velocity along the path. When off, the velocity of the object along the path varies depending on the distance between the vertices on the path.
Loop: By default, when the constrained object reaches the end of a path it can no longer move past the end point. The loop option changes this behavior so that when the constrained object reaches the end of the path it loops back to the starting point.
Relative: Turn on to maintain the original position of the constrained object. The object will follow the path with an offset distance based on its original world space position.
Axis: Defines which axis of the object is aligned to the trajectory of the path.
Flip: Turn on to flip the direction of the axis.