You set whether a joint
behaves as a hinge, a drawer slide, or another type of joint by
joint parameters for
each object in the kinematic chain. Joints control the rotation
and position of an object with respect to its parent.
Any object has a maximum
of two joint-type rollouts: One rollout contains settings to control
the object's position, and the other controls the object's rotation.
There can be many different types of positional and rotational joints.
Which joint parameters are available is determined by the type of
IK solver assigned to an object. HI Solvers, for instance, are controlled
with a preferred angle setting found in the Rotational Joint parameters.
HD Solvers have additional parameters for spring back, precedence,
and damping, not found in the HI Solver.
Any hierarchy of object
or bone systems can have its joint limits defined. Select all the
objects, and turn on their bone or link display. Select the bone
or link and open the Hierarchy panel IK
tab. Scroll down to the Sliding and Rotational Joints. There, you
can activate axes and set their individual limits.
NoteDifferent IK solvers
use different joint limits. When using a bone system, add the IK
solvers first, then set the joint limits second.
Common Joint Types
The most common joint
types are Rotational and Sliding joints. Other common joint types
are Path and Surface joints. Each joint type displays its own set
of joint parameters.
- Rotational joints
Control rotation of objects
using many of the standard rotation controllers. The parameters
for rotational joints set an object's ability to rotate about a
For many IK structures,
consider using an
XYZ controller. Quaternion-based controllers
tend to freeze if an object is moved beyond rotational joint limits before
turning on IK.
- Sliding joints
Control the position
of objects using many of the standard position controllers. The
parameters for sliding joints control whether an object can move
along a given axis.
- Surface joints
Control the position
of objects using
constraint. The parameters control how
the object travels along its assigned surface.
- Path joints
Control the positional motion
of objects using
constraint. The parameters for path joints
control how far an object can travel along its assigned path.
Using Joint Parameters
The way the children
behave toward one another is governed by the inheritance of the
transforms down the chain. Setting joint limits on
individual child objects can influence this inheritance. If three
children in a row all have their rotational axes made inactive,
they will not be able to rotate, and so a piece of the chain will
appear stiff. Or if only one axis is made active as a sliding joint,
the component can separate in space from the chain.
When you are using an
object with a path constraint in an IK chain you might want the
path to appear as if it is part of the IK chain. You achieve this
effect by linking the object using the path constraint and the path
to the same parent. The path object should have no children, and
other objects in the IK chain should be linked to the object using
the path constraint.
In the figure, the bead
uses a path constraint to hold it to the ring. The IK chain from
parent to child is Post->Cap->Bead->Handle. The ring is
a child of the Cap but is not part of the IK chain.
Copying and Pasting Joint
You can copy and paste
at the bottom of the Object Parameters rollout in the Hierarchy
panel to copy and paste a complete set of joint parameters from
one object to another.
There are separate copy
and paste functions for sliding joints and rotational joints. Each
joint type saves copied parameters in separate clipboards.
Choose one of the
Mirror Paste options if you want to mirror the joint parameter settings
as you paste them. This is very useful when pasting from one side
of an object to another, such as left arm joints to a right arm.
You can also copy joint
settings from a non-IK controller to an IK controller, but you can't
copy from an IK controller to a non-IK controller.