8
Animating by Rotating Links 751
• Rotations on the new pelvic axes (X and Z) are
keyable in layers a nd supported in MAXScript.
• The default parametric footstep animation is
slightly adjusted to use the three-DOF p elv is.
• If a legacy biped asset such as a BIP file i s loaded
onto the 3ds Max biped, the pelvis-related
data will be adapted to the new DOFs and the
new coordinate space within which the pelvis
rotates.
• Using the Motion Mixer or Motion Flow, assets
containing new pelvic rotation tracks will be
blended with old assets lacking t hese tracks.
Sp eci a l Rot ati on: El bows a nd K nees
Elbows and Knees per form a special rotation
when you rotate them about their X axis. They
don’t actually rotate around their X axis; this does
notmakesensebecausetheyhaveonedegreeof
freedom. Instead, the upper and lower arm/leg are
rotated together about an invisible axis defined by
the line stretching from the shoulder to the wrist,
and the hip to the ankle. This special rotation can
be ver y useful for positioning the arms and legs.
The special rotation can also be useful for creating
characters w ith reve rse knee bends. When the
knees are rotated backward, at more than a
90-degree rotation from the front-facing h uman
knee posture, Biped assumes the character has
backward k nees or bird legs, and uses this as a
reference position for all .
bip
motions.
Rotating the forearm along the X axis rotates the arm
elements about an invisible axis between the shoulder and
wrist.
B alance: S pine
Biped uses only the spine, in conjunction with the
center of mass, to maintain the biped’s balance.
Because of this, rotating all of the spine or any one
of its links causes the horizontal position of the
body to change relative to its center of mass. These
adjustments are performed in the center of mass’s
local reference coordinate system, ensuring that
the figure will rotate naturally about its center of
mass; for example, during flips in the air.
On the Motion panel
Key Info rollout (page
2–809)
,youcanturnthisbehavioroffbysetting
Balance Factor to 0.0 for corresponding horizontal
cent er of mass keys. The Balance Factor control is
intheBodygroupontherollout.
Ind ependent Or ient ati on: Ar ms, Hea d,
Fee t
Changing the orientation of a clavicle (the root
Arm object) changes the position, but not t he
orientation, of its corresponding upper arm. In
effect, the clavicles are a support from which the
arms are suspended.