3ds Max 2012 Bible - Kelly L. Murdock [419]
Note
The original Character Studio package used the Physique modifier to bind the mesh skin to the biped. Although this modifier still exists and can be used, the Skin modifier includes many new features and is the preferred method for binding a mesh skin to the biped. •
The next step is to animate the rig using its animation tools, which can include walk, run, and jump cycles using keys. Along the way, you can save, load, and reuse animation sequences, including motion capture files. Animated sequences can be combined and mixed together to form a smooth-flowing animation using the Motion Mixer.
Creating a CAT Rig
Creating a hierarchical skeleton that is used to control the animation of the mesh skin that is draped over it is quite easy using CAT. The skeleton can be set to be invisible in the final render and exists only to make the process of animating easier. Although Max includes a robust set of tools that can be used to create a skeleton of bones, CAT features automate this entire process and even include a number of prebuilt skeletons.
Cross-Reference
For some characters, modifying a prebuilt skeleton is more work than building a custom skeleton. For these occasions, you can manually create a skeleton structure. Building a rig system by hand is covered in Chapter 38, “Understanding Rigging, Kinematics, and Working with Bones.” •
Using prebuilt CAT rigs
To add a prebuilt CAT rig to the scene, simply open the Create panel and select the Helpers category. When you choose the CAT Objects subcategory, you have three options: CAT Parent, CAT Muscle, and Muscle Strand. Click the CAT Parent button and drag in the viewport to place the CAT Parent object. This parent is simply an icon used to control the global position of the rig and is not rendered.
Tip
It is best to place the CAT Parent object at the origin of the scene. •
While the CAT Parent object is selected, you can choose a preset rig from the list in the CAT Rig Load Save rollout in the Modify panel or you can select a preset before creating a CAT parent to make the specified preset. The size of the rig is determined by how far you drag in the viewport, or you can set the size using the CATUnits Ratio value in the Command Panel. These custom rigs include a variety of human-shaped and animal-shaped rigs, such as the Alien rig shown in Figure 39.1.
FIGURE 39.1
CAT includes several default preset rigs such as this alien character.
One key advantage of CAT rigs over the rigs available in Character Studio and Biped is that they aren't limited in their structure. Although the available CAT rig presets includes a Base Human and even a Bip01 rig that are used for animating human characters, some of the other presets are dragon, horse, lizard, spider, and centipede. These different rigs have multiple legs, arms, and wings and all are easily controlled.
Modifying prebuilt CAT rigs
With a prebuilt rig added to the scene, you can use the Transform tools to select and move the bones to match the skin mesh. The arms are automatically set up as a Forward Kinematics (FK) chain, so rotating the upper arm bone automatically rotates the rest of the arm bones with it. The legs are set up with an Inverse Kinematics (IK) chain, so you can position the legs by dragging the feet, and the rest of the leg bones follow. By default, all CAT prebuilt rigs have stretchy bones, so if you select and move a bone, the selected and attached bones stretch to maintain the joint connection.
Tip
If you double-click a bone, the bone and all its children are selected. For example, double-clicking a collar bone selects the entire arm, making it easy to move the whole arm into place. •
A CAT rig keeps track of the different types of body parts and presents the appropriate set of parameters depending on which bone is selected. For example, if you select any part of the arm, the Limb Setup rollouts appear in the Modify panel. This rollout has