2009

History-Dependent (HD) IK Solver
Select a node of hierarchy or bone chain. > Animation menu > IK Solvers >
HD Solver > Click a second node of chain.
Animating with the HD Solver lets you use sliding joints combined with
inverse kinematics. It has controls for spring back, damping, and precedence
not found in the HI Solver. It also has quick tools for viewing the initial state
of the IK chain. Use it for animations of machines and other assemblies. Since
this is history dependent, performance is slower at the end of long animations.
For lengthy scenes, use HI Solvers, if possible.
Animating the End Effectors
You animate a hierarchy of objects or bone structure using HD Solvers by
animating special end effectors located at the bone joints. There are two types
of end effectors: Position and Rotation. They are displayed as three intersecting
blue lines at the joint.
When you select and transform a joint that carries either end effector, only
the end effector itself is transformed. The objects or bones in the chain then
use IK to calculate the IK solution.
Animating these end effectors is much like animating with Interactive IK
except interpolation between keyframes uses correct IK solutions.
Linking End Effectors to a Parent
You can link HD IK end effectors to a parent to achieve results similar to using
bound follow objects with Interactive and Applied IK. To link a HD IK end
effector, you click Link on the Motion panel.
There are two reasons to link an end effector to a parent:
You can rescale your entire hierarchy. If you animate a robot, and then
later decide you want to scale the entire robot and its animation, link the
robot's root object to a dummy, link all of the robot's end effectors to the
same dummy, and then scale the dummy to scale all of the hierarchical
objects as well as the animation of the end effectors.
You can use linked end effectors for things like feet or hands. End-effectors
are automatically bound to the world, so when you move a root object in
your hierarchy, the end effectors remain behind. This is good for keeping
feet on the ground, but not very good for hands, where you want them to
3422 | Chapter 15 Animation