2009

You always start transforming objects at the highest-level parent affected by
the motion and work your way down the hierarchy to the last child.
You have considerable control over the exact placement of every object in
the hierarchy using forward kinematics. However, the process can become
tedious with large and complex hierarchies. In such situations, you might
want to use
inverse kinematics on page 3374.
Using Dummy Objects
The primary use of
dummy helper objects on page 2615 is to assist in creating
complex motions and building complex hierarchies. Because dummies are
invisible when rendered, they are an excellent choice for offset joints,
connectors between objects, and handles for complex hierarchies. Dummies
and
Points on page 2628 can act as null objects that function as controls for
transforming parts of an IK chain.
Using a Dummy to Control Motion
Breaking complex motions into simple components often makes it easier to
go back and edit your animations.
Consider a bouncing ball that moves along a path. You could animate the
ball by positioning it on many frames, but it would be very difficult for you
to go back and adjust the height of the bounce or the path of the ball. You
have to edit the motion of the ball on many frames to make even a simple
change.
Using a dummy object solves this problem by breaking the motion into simple
components. One component is the up and down bounce of the ball. The
other is movement on the path.
Animating with Forward Kinematics | 3363