When you use footsteps to animate the legs and feet, animating the spine, neck, head, arms, and other upper body parts is accomplished in the same way as for freeform animation. Simply turn on Auto Key and start moving and rotating body parts. See Animating by Moving Links and Animating by Rotating Links.
You can also click the Set Key button on the Key Info rollout to set keys for selected body parts at the current frame. This option allows you to move body parts as you like, setting keys only when you have decided to do so.
Do not use the 3ds Max Set Key button to set keys for the biped. Animation on the center of mass (COM) works differently, depending on whether the biped is in a footstep at that particular frame.
- If at least one foot is in a footstep, moving or rotating the COM will animate the entire body along with the COM, except a foot that is in a footstep. A foot in a footstep will stay planted in the footstep and the leg will bend or straighten as the COM is moved up or down.
- If the biped is airborne (no footsteps at that frame), the COM can be moved horizontally and can be rotated, but cannot be moved vertically. This is because character studio automatically calculates how high the biped can go based on the biped's height and the current gravity setting. To make the biped jump higher or lower during airborne periods, see Freeform Animation Between Footsteps.
Working with Existing Keys
Because keys are created for the spine, arms, and tail when footsteps are activated, you will want to take care when creating new keyframes. As with 3ds Max animation, placing keyframes one or two frames apart creates jerking or popping motions.
To avoid placing keyframes on upper body parts too close together, you can do one of the following:
- Turn on the 3ds Max
(Key Mode Toggle), select the body part, and use Next Key and Previous Key to move in time from one keyframe to another. Animate only on existing keyframes. - Delete all the body part keys except the key at frame 0, and create entirely new keys throughout the animation. Warning: If you delete all keys, including the key at frame 0, be sure to set a key at frame 0 before animating on other frames. character studio does not automatically place a key at frame 0 when you animate on frames other than 0, as 3ds Max does.
Interdependencies Between Legs and Upper Body
When footstep animation is used, animation of the upper body and animation of the legs are interdependent. Any time you change the position of the body's center of mass, leg positions are automatically updated to ensure the feet still move from footstep to footstep.
Interdependencies between the upper body and legs are updated after a key has been set, sometimes causing the appearance of a pop in the leg position. However, in playing the animation you will find the motion to be smooth.
When you set a leg key while the foot is on the ground, the location of the foot is automatically recalculated based on the natural roll of the foot from its point of initial contact with the ground. The pivot points are based on collisions between the footstep plane, the two corners of the heel, and the bones that connect the toes' links.
This ability to preserve interdependent relationships allows you easily to experiment and improvise with motion, since you are assured that edits to one body part will not corrupt the integrity of other parts.
In general, changes to the center of mass, spine, and pelvis cause the legs to adjust. Changes to the legs do not affect the center of mass's vertical position.