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486 Chapter 12: Animation
Activating S liding Joints
1. Sliding axis
WhenyouturnonActiveforoneoftheX,Y,Z
axes of a sliding joint the object can move a long
that axis of its p arent’s coordinate system.
Most sliding joints are active only along a single
axis. A telescope is an example of a sliding joint
active on a single axis. You rarely see a sliding joint
active along all three axes.
If a sliding joint is active along all three axes, it
moves independently from its pa rent. It’s almost
as if there is no joint connection at all.
Tip: Use the HD IK Solver when you need to use
sliding joints with IK.
Path and S ur face Joints
Circular path
WhenyouturnonActiveforPathorSurfacejoints
you are setting whether the object can move along
the assig n ed path or surface.
A house key on a ring is an example of an ac tive
path joint.
See Path Constraint (page 2–398).
Limiting Joint Action
Most joints are limited in their range of motion
along an active axis. For example: a hinge might
open only to 120 degrees; a piston slides only
w ithin the leng th of its cylinder. To limit the range
of motion allowed on an active axis, you turn on
Limited and set values for the From and To fields
on the joint rollouts.
You can also view joint limits in the viewport by
pressing and holding the mouse button on the
From or To label of a limit field. The object will
move or rotate to the limit value until you release
the mouse button.
Limiting R otational Joints
Limits for a rotational joint define how far the
object can rotate about its parent’s axes. The
values in the From and To fields represent the
rotation angle about the active axis measured from
0 degrees on the parent object.
For example, a n elbow joint rotates the forearm
w ith respect to the upper arm. In the figure the
limits on X axis rotation are from 0 to 135 degrees.
TheY,Zaxesareinactivebecauseanelbowjoint
rotates about a single axis.
Limi ting S l iding J oints
Limits for a sliding joint defi ne how far a joint
canmovealongitsparent’saxes. Thevaluesin
the From and To fields represent a distance for
movement along the active axis measured f rom