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History-Dependent (HD) IK Solver 461
Histor y -Dependent (HD) IK
Select a node of hierarchy or bone chain. > Animation
menu > IK Solvers > HD S olver > 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
forviewingtheinitialstateoftheIKchain.Useit
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 S olvers, if possible.
Animating the End Effectors
You animate a hierarch y of objects or bone
struc ture using HD Solvers by animating special
end effectors located at the bone joints. There are
two types of end effectors: Position and Rotat ion.
They are displayed as three intersec ting 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
thenuseIKtocalculatetheIKsolution.
Animating these end effectors is much like
animating with Interactive IK except interpolation
between keyframes uses correct IK solutions.
Li nking En d E f fector s t o a Par ent
You can link HD IK end effectors to a parent
to achieve results simi lar to using bound follow
objects with Interac tive and Applied IK. To link a
HD IK end effector, you click Link on the Motion
panel.
There are two reasons to li nk an end effector to
aparent:
• 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
therobot’sendeffectorstothesamedummy,
andthenscalethedummytoscaleallofthe
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 hierarch y, the end effectors
remain behind. This is good for keeping feet
on the ground, but not very good for hands,
where you wan t them to mov e along with the
character. To have hands follow the root objec t ,
link the end effectors of the hands to the root
object.
Linking B ones to Follow Objects
You can also use follow objects instead of end
effectors and bind bones to any number of follow
objects using Interactive IK.
If you use follow objects with HD IK, you do not
need to click Apply IK. The IK solver t akes care of
everything automatically.
See also
Inverse Kinemat ics Rollout (page 2–497)
Binding Objects (HD Solver)
Use the binding functions (page 2–492) in the HD
Solver to cause an object to attempt to maintain its
position and orien tation relative to the world or to
another object. A bound object will resist motion
in the kinematic chain until the chain is stretched
near its limits and the bound object must move to
complete the IK solution.