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Rubber-Banding the Center of Mass

When Rubber Band mode is active, you can move the biped's center of mass in relation to the rest of the body, changing the biped's overall balance. Rubber banding the center of mass defines your character's balance point in at-rest pose and in any resulting motion.

When a character is standing at rest, with feet side by side, the center of mass should be directly above the area where the feet touch the ground. The center of mass determines the center of your character's distribution of weight. For most characters, this is typically located near the pelvis.

Typical placements for the center of mass are:

Characters that stand erect, such as humanoids, use the default location of the center of mass within the pelvis.
Characters that naturally lean forward, such as some dinosaurs and birds, should have the center of mass moved slightly forward of the pelvis. This is also good for robots and droid soldiers.
Characters that are holding a heavy weight out in front of them may need their center of mass moved slightly forward of the pelvis.
Characters that are pushing or pulling objects may need their center of mass moved slightly behind the pelvis.
Note: If you place the center of mass too far in front of the pelvis, the character unnaturally compensates for balance. As each step is taken, the legs and body move in an awkward fashion, as if there was an invisible weight attached to the front of the character.

Effects of Rubberbanding the Center Mass behind and before the biped

For a tutorial that uses this technique, see Creating the Illusion of Weight.

Balance Factor

Use Rubber Band mode to position the biped's center of mass in relation to the rest of the body. Then set the Balance Factor in the Key Info rollout to fine tune the biped's balance.

Balance Factor can be animated. If a character is sitting down and stands up, Balance Factor could change from 0 to the default of 1 to account for the shift in weight.

At a value of 0, the spine bends forward, pivoting at the center of mass. The character's weight is supported by the chair.
At a value of 1 the pelvis shifts away from the center of mass as the spine bends forward to maintain balance. The character, no longer supported by the chair, must adjust body position to maintain balance.