9

Animating by Rotating Links 893
• Rotations on the new pelvic a xes (X and Z) are
keyable in layers and supported in MAXScr ipt.
• The default parametric footstep animation is
slightly adjusted to use the three-DOF pelvis.
• If a legacy biped asset such as a BIP file is loaded
onto the 3ds Max biped, the pelvis-related
data will be adapted to the new DOFs and the
new co ordinate space within which the pelvis
rotates.
• Using the Motion Mixer or Motion Flow, assets
containing new pelvic rotation tr acks will b e
blended with old assets lacking these tracks.
Sp eci a l R ota ti on: E lbows a nd Kn ees
Elbows and Knees perform 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 posit ioning the arms and legs.
The special rotation can also be useful for creating
characters with reverse knee bends. When the
knees are rotated backward, at more than a
90-degree rotation from the front-facing human
knee posture, Biped assumes the character has
backward knees 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 p erformed in the center of mass’s
local reference coordinat e system, ensuring that
the figure will rotate naturally about its center of
mass; for example, during flips in the air.
On the Motion panel Ke y Info rollout (page 2–954),
you can turn this behavior off by setting Balance
Factor to 0.0 for corresponding horizontal center
of mass keys. The Balance Factor control is in the
Body group on the rollout.
Ind ependent Or i enta ti on: A r ms, Hea d,
Fee t
Changing the orientation of a clavicle (the root
Arm object) changes the position, but not the
orientation, of its corresponding upper arm. In
effect, the clavicles are a support from which the
arms are suspe nded.