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Adjust IK motion constraints
To
create more realistic motion of IK armatures, you can control the
freedom of motion of specific bones. For example, two bones that
are part of an arm could be constrained so that the elbow cannot
bend in the wrong direction.
By default, each IK bone has
a fixed length assigned when the bone was created. Bones can rotate
around their parent joint and along the x and y axis, but they cannot
move in ways that require the length of their parent bone to change.
You
can enable, disable, and constrain the rotation of a bone and its
motion along the x or y axis. By default, bone rotation is enabled
and x and y axis motion are disabled. When x or y axis motion is
enabled, a bone can move along the x or y axis to an unlimited degree,
and the length of the parent bone changes to accommodate the motion.
You
can also limit the speed of motion of a bone to create the effect
of weight in a bone.
You set these properties in the Property
inspector when one or more bones are selected.
To enable a selected
bone to move along the x or y axis and change the length of its
parent bone, select Enable in the Joint: X Translation or Joint:
Y Translation section of the Property inspector.
A two-headed
arrow appears perpendicular to the bone on the joint to indicate
that x axis motion is enabled. A two-headed arrow appears parallel
to the bone on the joint to indicate that y-axis motion is enabled.
If you enable both x and y-translation for a bone, it is easier
to position the bone when rotation is disabled for the bone.
To limit the amount of motion enabled along the x or y axis,
select Constrain in the Joint: X Translation or Joint: Y Translation
section of the Property inspector and enter a value for the minimum
and maximum distance the bone can travel.
To disable rotation of the selected bone around the joint,
deselect the Enable checkbox in the Joint: Rotation section of the
Property inspector.
This checkbox is selected by default.
To constrain rotation of a bone, enter minimum and maximum
degrees of rotation in the Joint: Rotation section of the Property
inspector.
The degrees of rotation are relative to the parent
bone. An arc appears on top of the bone joint indicating the degrees
of freedom of rotation.
To make a selected bone stationary relative to its parent
bone, disable rotation and x and y-axis translation.
The bone
becomes rigid and follows the motion of its parent.
To limit the speed of motion of a selected bone, enter a
value in the Joint Speed field in the Property inspector.
Joint
speed gives the bone the effect of weight. The maximum value of
100% is equivalent to unlimited speed.
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