8

Activating Joint Axes 467
In the figure, the bead uses a path constraint to
holdittothering.TheIKchainfromparentto
child is Post->Cap->Bead->Handle. The ring is a
childoftheCapbutisnotpartoftheIKchain.
Copy ing a nd Past ing Joint Par ameter s
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.
Tip: Cho ose 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 ar m
joints to a r ight arm.
You can also copy joint settings from a non-IK
controller to an IK controller , but you can’t copy
from an IK con troller to a non-IK controller.
Activati ng Joint Axes
You set whether an object can move or rotate
aboutagivenaxisbyusingtheActivecheckbox
in the joint rollouts. Joints have a maximum of
six possible axes: three for rotation and three for
position. You constrain the motion of a joint by
setting w hich axes are active.
• A joint with all axes active can move and rotate
freely, independent of its parent.
• A joint with all axes inactive is locked to its
parent and cannot move independently.
• ThesettingofIKjointaxesoverridesInherit
and Lock sett ings on t he Link Info rollout.
Understanding Joint Axis Orientation
IK joint axes for an object are defined by the Lo cal
axes of the object’s parent. That means if you
activate the X axis of an object’s rotational joint
parameters, the object rotates about its parent’s X
axis, not its own X axis.
Youmighthaveaproblemwhenyousetjoint
parameters fo r an object whose local coordinate
system is oriented 90 degrees from its parent’s
coordinate system. In such a case, the rotation
angleaboutoneaxisbecomesindeterminate.The
resultisthatoneaxiswilloftencauserotation
about one of the other two axes.
The following techniques w i ll make setting joint
parameters easier and more successful:
• Assemble IK hierarchies with objects aligned
along the World axes.
•Considerusingthe
Adjust Pivot (page 2–470)
functions to align your object pivots with
either the World axes or the root object of the
hierarchy.
•SetthetransformmanagerstoParent
coordinate system and Use Pivot Point C e nter,
while setting joint parameters. This helps
you see the orientation of the joint axes by
displaying the parent axis icon at the selected
object’s pivot point.
• When activating joint axes, drag the From
spinner up and down. This causes the object
to move or rotate about the active axis and is a
quick check that you chose the right axis.