3ds Max 2012 Bible - Kelly L. Murdock [406]
Learning to work with the HI, HD, and IK Limb solvers
Building a bones system
Setting bone parameters and IK Solvers
Making linked objects into a bones system
What does a graveyard have in common with animated characters? The answer is bones. Bones are used as an underlying structure attached to a character that is to be animated. By using a bones structure, you can produce complex character motions by simply animating the bones and not having to move all the vertices associated with a high-resolution character.
Although Max includes a prebuilt skeleton with its Biped and CAT systems, at times you may want to build a custom bones system because not all characters stand on two feet. Have you ever seen a sci-fi movie in which the alien was less than humanlike? If your character can't be created by modifying a biped, then you need to use the traditional manual methods of rigging.
This chapter focuses on the process of manually rigging a character that, depending on the complexity of your character, could end up being even easier than working with bipeds. It also gives you a clear idea of concepts of rigging.
This chapter also presents the idea of kinematics. Kinematics is a branch of mechanics that deals with the motions of a system of objects, so inverse kinematics is its evil twin brother that deals with the non-motion of a system of objects, right? Well, not exactly.
In Max, a system of objects is a bunch of objects that are linked together. After a system is built and the parameters of the links are defined, the motions of all the pieces below the parent object can be determined as the parent moves, using kinematics formulas.
Inverse kinematics (IK) is similar, except that it determines all the motions of objects in a system when the last object in the hierarchy chain is moved. The position of the last object, such as a finger or a foot, is typically the one you're concerned with. With IK, you can use these solutions to animate the system of objects by moving the last object in the system.
Creating a Rigging Workflow
A rigged character starts with a linked hierarchy. A linked hierarchy attaches, or links, one object to another and makes it possible to transform the attached object by moving the one to which it is linked. The arm is a classic example of a linked hierarchy: When the shoulder rotates, so do the elbow, wrist, and fingers. Establishing linked hierarchies can make moving, positioning, and animating many objects easy.
A bones system is a unique case of a linked hierarchy that has a specific structure. You can create a structure of bones from an existing hierarchy, or you can create a bones system and attach objects to it. A key advantage of a bones system is that you can use IK (inverse kinematics) Solvers to manipulate and animate the structure. These IK Solvers enable the parents to rotate when the children are moved. In this way, the IK Solver maintains the chain integrity. Another advantage of a bones structure is that you can constrain the motion of bones so the motion is forced to be realistic, just like a real character.
After the bone structure is created, it needs to be edited to fit the skin mesh that it will control. You also need to define the limits of each bone and joint. This helps prevent the skeleton from moving in unrealistic ways. Applying IK systems is another way to control the motion of the bones and joints. This process of creating a skeleton structure and defining its limits is called rigging.
After you've edited a system of bones, you can cover the bones with objects that have the Skin modifier applied. This modifier lets the covering object move and bend with the bones structure underneath. The process of attaching a model to a bones system is called skinning.
Cross-Reference
The Skin modifier is covered, along with other aspects of skinning a character, in Chapter 40, “Skinning Characters.” •
After a character is rigged and skinned, the character is ready to be animated.
Building a Bones System
In some instances,