Graphics Reference
In-Depth Information
Figure 9.26 The secondary arm, IK constrained, with the primary FK arm in place.
This should make all of the bones in the armature disappear except the two new arm bones and the arm's
IK controller. Change to Pose mode, select the IK controller followed by the lower arm bone, and use
Shift-I to add an IK constraint. Immediately set the Chain Length property of the lower arm's IK con-
straint to 2 in the Bone Constraint properties. This constrains the lower arm bone to follow the IK con-
troller. Moving the controller causes the arm to move, just like the legs. While you're showing only this
bone layer, name the new arm bones. I would suggest “arm_upper_ik_L” and “arm_lower_ik_L.”
Staying in Pose mode, Shift select bone layer 1 in the Armature context so that both bone layers 1 and 5
are shown. Grab the IK controller for the arm and move it a bit. If you don't, the bones of both sets of
arms will overlap exactly and it will be hard to tell what is what. Figure 9.26 shows this structure. What
we're going to do now is apply constraints to each bone of the primary (FK) arm: Copy Location and
Copy Rotation . The lower arm is always attached to the upper, so we only need a Copy Rotation
constraint on it.
To do this, RMB select the secondary (IK) lower arm, then Shift-RMB select the primary lower arm.
Add a Copy Rotation constraint by pressing Shift-Ctrl-C (or doing it by hand in the Bone Constraints
context) and choosing Copy Rotation . The bone will probably change its orientation. Over in the Bone
Constraint context, examine the new Copy Rotation constraint, shown in Figure 9.27 . It holds a lot
of imposing options, but the constraint's main function is to make one bone orient itself exactly like its
target bone. The control that we're concerned with is called Influence, , at the bottom of the panel. Reduce
it from 1.0 (the default) to 0.0. Notice when you do that the bone in the 3D view reverts to its original
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