Tutorial 4: Animating Bipeds interacting with Objects
There are two techniques in character studio that give the illusion of weight to an animation. Both affect the biped center of mass.
The first technique uses the Balance Factor, which moves the center of mass. Balance Factor is available the Body Horizontal track. This technique creates the illusion of lifting a heavy object. It lets you keyframe the center of mass moving in and out of the body.
The second technique uses Figure mode to turn on Rubber Band. You move the center of mass in front of or behind the body. You can't keyframe the center of mass with this technique. It creates the illusion of the biped pushing or dragging a heavy object.
Two bipeds have planted keys set on their feet, with the pivot points set at their toes.
Select any part of the biped on the left and then open the Motion panel.
Using Balance Factor
Select the Body Horizontal track.
In the Key Info rollout, set Balance Factor to 0.
The Balance Factor is available because this file contains a keyframe on the Body Horizontal track at frame 0.
At frame 15, turn on Animate.
Select Bip01 Spine object (the first spine object).
Rotate the spine about the Z axis.
Only the upper body rotates
Notice that the upper body rotates, the legs stay firmly planted.
Animating the Balance Factor
Select the other biped.
In the Track Selection rollout, select Body Horizontal.
In Key Info rollout, click set key.
Now Balance Factor is available.
Change the Balance Factor to 2.
Select Bip02 Spine.
Rotate the spine again.
Hips move back, torso rotates forwards.
This time the hips move back as the torso rotates forward. If you rotate the torso enough, the feet move off the floor.
Notice also that the center of mass is now in front of the body.
Select Body Vertical and move the center of mass down, so the knees are bent.
At frame 23, rotate the Bip02 Spine more, so the knees touch the chest.
Move the center of mass farther away from the body.
Center of Mass moves away from the body
The biped leans over even more.
At frame 30, move the center of mass so the biped starts to lift the imaginary object using its legs, rather than its back.
At frame 38 in the Track Selection rollout, select the Body Horizontal track..
On the Key Info rollout click set key.
Change the Balance Factor to 1.
The center of mass moves back closer to the biped.
Select and rotate the spine.
At frame 45, rotate the spine more.
Move the center of mass so the biped stands up straight. Now the center of mass is back inside the body.
Move the time slider back and forth to the animation.
Watch how the center of mass moves outside the biped, then back again.
The biped appears to be lifting something heavy because of the positioning of the knees and spine.
Play the animation.
The biped is pushing a box along the floor. Notice that the center of mass is behind the biped.
Adjusting the center of mass in Figure Mode with Rubber Band
Select any part of the biped.
In the Motion panel, turn on Figure mode.
In Track Selection, choose Body Horizontal.
Turn on Rubber Band mode and move the biped's center of mass so it is back inside the body.
Turn off Figure mode and play the animation.
The upper torso moves back over the feet. The illusion of weight is diminished.
Turn on Figure mode and move the center of mass far behind the body.
Turn off Figure Mode.
The biped leans into the box, as though the box were quite heavy.
Lesson 5: Using In Place Mode