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 move along with the character. To have hands follow the root object, link the end effectors of the hands to the root object.
Linking Bones 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 takes care of everything automatically.
