The geometry of a biped is a linked hierarchy of objects that by default resemble those of a human. The parent or root object of the biped is its center of mass (COM). This object is displayed as an octahedron near the center of the biped's pelvis. Moving the COM positions the entire biped.
Center of Mass Object
You can select the center of mass by choosing Bip01 from the select by name dialog. You can also select the center of mass by choosing either the Body Vertical, Body Horizontal or Body Rotation buttons in the Track Selection Rollout. These will select the center of mass as well as the particular track you wish to change.
The center of mass uses three animation tracks. Two of these tracks, Body Vertical and Body Horizontal, contain Biped Dynamics options.
The Body Vertical track uses the Dynamics Blend parameter to control gravity in a footstep animation. A Dynamics Blend value of 1 uses the value of GravAccel (global gravity value) to calculate an airborne trajectory for the biped. No keyframes are required to position the biped in the air, a trajectory is calculated automatically. A value of 0 uses Spline Dynamics for the vertical position of the biped; you must create keyframes to position the biped vertically.
The Body Vertical track also has a Ballistic Tension parameter that controls how much the biped knees bend when the biped lands from an airborne period. This means that keys do not need to be created at the lowest position of the biped after landing, a trajectory is calculated automatically.
Note: Keys can be created manually to override the calculated trajectory during the landing period. However, vertical keys must be set to Dynamics Blend=0.0 in order to fully override the trajectory during the airborne period.
The Body Horizontal track has a Balance Factor parameter that automatically orients the biped to maintain balance. This saves the animator from having to reposition the pelvis when the biped leans forward, backwards, or sideways.
Note: Biped Dynamics parameters can be animated from no effect to full effect at each keyframe.
If you are starting a new footstep animation, but would prefer to use Spline Dynamics rather than the default Biped Dynamics, then turn on Spline Dynamics in the Animation Properties rollout before creating any footsteps.
If you are starting a freeform animation (no footsteps), only Balance Factor is available. Freeform animation uses Spline Dynamics for Center of Mass positions.
The biped Hierarchy is a little different than your standard 3DS MAX hierarchy in that you can't delete any of the components of the skeleton. If you try to delete any of the biped skeleton, you delete the entire hierarchy. If you want to create a partial biped, for example a biped with no head, simply hide the objects you don't want to see.
Certain Biped body parts can be repositioned in figure mode to suit different characters. You can move entire arm assemblies by selecting the clavicles and moving them up or down. You can also reposition the fingers, tail and ponytails as you like.
To add extra legs, arms or other body parts you need to create 3DS MAX geometry for those parts, then link them to the biped hierarchy. You can use Snapshot to duplicate biped body parts to create these as well. In either case you will need to animate them with standard MAX rotations, biped IK will not be available on these extra parts.