3ds Max 2012 Bible - Kelly L. Murdock [267]
3. Select the dummy object, choose Animation⇒Constraints⇒Surface Constraint, and select the hill object.
4. In the Surface Controller Parameters rollout, select the Align to V and Flip options to position the dummy and tire objects at the top of the hill. Set the V Position value to 50 to move the tire down the hill.
5. Click the Auto Key button (or press the N key), drag the Time Slider to frame 100, and change the U Position to 100. Click the Animate button again to deactivate it, and click the Play Animation button to see the tire move down the hill.
Figure 22.2 shows the tire as it moves down the hill. In the Top view, you can see the function curves for this motion.
FIGURE 22.2
The Surface constraint can animate one object moving across the surface of another.
Path constraint
The Path constraint lets you select a spline path for the object to follow. The object is locked to the path and follows it even if the spline is changed. This is one of the most useful constraints because you can control the exact motion of an object using a spline. With Max's spline features, you can control very precisely the motions of objects that are constrained with the Path constraint. A good example of this constraint is an animated train following a track. Using a spline to create the train tracks, you can easily animate the train using the Path constraint.
When you choose the Animation⇒Constraints⇒Path Constraint menu command, you can select a single path for the object to follow. This path is added to a list of paths in the Path Parameters rollout.
The Path Parameters rollout also includes Add and Delete Path buttons for adding and deleting paths to and from the list. If two paths are added to the list, then the object follows the position centered between these two paths. By adjusting the Weight value for each path, you can make the object favor a specific path.
The Path Options include a % Along Path value for defining the object's position along the path. This value ranges from 0 at one end to 100 at the other end. The Follow option causes the object to be aligned with the path as it moves, and the Bank option causes the object to rotate to simulate a banking motion.
The Bank Amount value sets the depth of the bank, and the Smoothness value determines how smooth the bank is. The Allow Upside Down option lets the object spin completely about the axis, and the Constant Velocity option keeps the speed regular. The Loop option returns the object to its original position for the last frame of the animation, setting up a looping animation sequence. The Relative option lets the object maintain its current position and does not move the object to the start of the path. From its original position, it follows the path from its relative position. At the bottom of the Path Parameters rollout, you can select the axis to use.
Tutorial: Creating a spaceship flight path
Another way to use splines is to create animation paths. As an example, you use a Line spline to create an animation path. You can use splines for animation paths in two ways. One way is to create a spline and have an object follow it using either the Path constraint or the Path Follow Space Warp. The first vertex of the spline marks the first frame of the animation. The other way is to animate an object and then edit the Trajectory path.
In this tutorial, you use a simple path and attach it to a spaceship model. Viewpoint Datalabs provided the spaceship model.
To attach an object to a spline path, follow these steps:
1. Open the Spaceship and asteroids.max file from the Chap 22 directory on the CD.
This file contains the spaceship model and several asteroid objects.
2. Select Create⇒Shapes⇒Line, and click and drag in the Top viewport to create an animation path that moves the spaceship through the asteroids. Right-click when the path is complete. Then select the Modify panel, click the Vertex button in the Selection rollout to enable Vertex subobject mode, and edit several vertices