General Rules About Creating Skeletons for Biped Characters

by Brian Immel

1. Joints should be placed relatively center of the area it is to control unless otherwise stated. Figure 1 illustrates a generic character skeleton system.

2. NAME EVERY JOINT ACCORDINGLY! If a joint is placed in the area of the spine, name it something that relates to the location (such as spine, shoulder, elbow, hip, knee, etc.).

3. Start with the center of the character’s gravity. Usually, a biped’s Root joint will located somewhere between the belly button (if he/she has one) and the belt buckle region).

4. Use good naming conventions (left, right, upper, lower, etc.). If a joint is on the left side of the body use a suffix of _L or _left or some other ID tag that tells the user that this joint is on the left side of the character. Personally, I use _L/_R for left and right sides respectively. Figure 2 shows the naming convention named according to the character’s POV (not the user’s) and where the Root joint is located.

5. Use real anatomy as a reference for how and where to place your joints. However, don’t use this idea as “be-all, end-all” answer to where to place your joints. Example, the human spine is located in the back of the torso but this may cause skinning issues if you place your spine joints in a similar location for your character.

6. Consider the types of joints each part of the human anatomy uses:

• Ball: allows for rotation in any direction.
• Hinge: allows for rotation in only one axis.
• Pivot: allows for an orbiting rotation.
• Ellipsoid: basically the same as ball except it has limited rotations.
• Non-moving: As humans, all of our joints play some role in the locomotion of our body movements. However in the case of CG skeletons, it is sometimes useful to place a joint that does not have any bending responsibilities but would serve us well for skinning and base locations for branching out.

7. When creating FK joints, think them as branches. Start with the root and work your way out. Figure 2b shows which direction these branches should created in.

• Spine should be created up from root to base of neck.
• Arms should be created out from base of neck to the palm joint.
• Legs should be created down from hip to the ankle.
• Foot should be created out from ankle to toe.
• Finger should be created out from palm joint to the tip of finger.
• Head should be created up or out from base of neck.