Rigging and Skinning - Animating with Blender: How to Create Short Animations from Start to Finish - page 133

A Practical Example

Figure 9.8 shows the controls for the Beast's
mother, without the mesh. The controls for a
character need to be created with a few things
in mind. First, the controls should fi t what the
character will be doing. Second, when ani-
mation has commenced and keyframes have
been created, the control structure cannot be
changed. Here are some guidelines to follow
when creating your rig and how they apply to
the mother.

Inverse Kinematics/Forward
Kinematics

Figure 9.8 The controls for the mother

By default, armatures are created using forward kinematics (FK), with several options for implementing inverse
kinematics (IK). IK is most useful when the end of a bone chain will be bearing weight. Technically, IK is used
when the end of a limb is required to have a fi xed-point in space, while the remainder of the limb is moving. This
can be a foot on the ground, a hand on a countertop, or a paw holding onto a tree limb. Obviously, most char-
acters will use this for their feet and legs. There are some exceptions, of course. In the case of the Beast himself,
the legs and feet use forward kinematics because he spends a lot of time sitting, or with his feet in the air. Also
note that the “weight-bearing” rule only applies to the tips of bone chains, not the roots. Even though a sitting
character's weight is supported by the base of its spine, that bone is usually a root of a chain, not a tip, so IK is not
appropriate. Unlike the Beast, the mother spends all of her time standing, so IK is appropriate for use on her legs.

If you examine Figure 9.8, you will
notice that the leg bones themselves are
not visible. That is because the anima-
tor does not directly interact with them.
Bones that are part of an IK chain are not
directly manipulable in any useful fashion.
Figure 9.9 shows the leg bones, which
fall under the helper category because
they translate the controls from Figure
9.8 into deformation. The legs and feet
are rigged with a standard method called
the reverse foot , which is shown in Figure
9.10. The reverse foot allows you to con-
trol the position and rotation of the foot,
as well as the extension of the ball of the
foot and toes, while having the leg react

Figure 9.9 The controls and helpers for the legs