Week 3 — Skeletons I: Joints, Orientation, Spine and Legs

Unit 1 Overview · Course Home · Previous: Week 2 · Next: Week 4

This week

Your first joints. More importantly, the rules that determine whether those joints will work or
quietly ruin the next twelve weeks.

Maya has joints, not bones

This one distinction explains everything else this week.

The "bone" you see drawn between two joints is a display artifact. There is no bone object in
Maya.

Which means: a joint's orientation is determined by the next joint in the chain. Move a child
joint and the parent's bone direction changes — but its jointOrient value does not update on
its own. And a joint with no child inherits its parent's orientation, because there is nothing for
it to point at.

jointOrient versus rotate

• jointOrient is where a joint's rest orientation lives.
• rotate is where animation lives.

At bind pose, rotate must read zero. If your orientation ends up stored in rotate, an
animator cannot get back to bind pose by zeroing channels — and that is the one thing every
animator expects to be able to do.

Turn on Display → Transform Display → Local Rotation Axes and leave it on all class.

The convention: X points down the bone, with the secondary axis consistent along the chain.
This will matter concretely in Week 10, when spline IK's twist controls turn out to require X as
the aim axis.

Positioning joints

The rule people break most often:

Position joints by moving them. Never by rotating them.

Rotating a joint to place it bakes a non-zero rotate value into your rest pose. And after you move
a joint, its orientation is stale — re-orient the chain.

Skeleton → Orient Joint options: primary axis, secondary axis, secondary axis world
orientation, and in Maya 2025+ an Auto orient secondary axis option that uses neighboring
joints. Orient the end joint to world so it carries no misleading orientation.

Evaluation order

Rotating a parent moves every descendant. Rotating a child moves nothing above it.

This is the same DAG behavior from the ball rig in Week 1, now with joints instead of groups.

When to redraw

Redrawing a skeleton is normal and cheap. Fighting a bad one is expensive.

If a chain's hierarchy is wrong, or its orientations cannot be salvaged, delete it and draw it
again. You will want to resist this. Don't. Ten minutes of redrawing beats three weeks of a
skeleton that fights you.

Placement

• Root at world origin, between the hips. Engines reject multi-root skeletons.
• Spine count and curvature — follow the actual S-curve, not a straight line.
• Hip, knee, ankle, ball, toe.
• Preferred angle: pre-bend the knee slightly forward. This tells the IK solver in Week 9
  which way the leg bends. A perfectly straight chain gives the solver nothing to work with and it
  will pick a direction you don't want.

Naming

Your joints get role suffixes starting now. See Naming Convention.

• root_jnt — the skeleton root
• spine_01_bnd … — deformation joints, which will carry skin weights
• L_hip_bnd, L_knee_bnd, L_ankle_bnd, L_ball_bnd
• L_toe_tip — a terminal joint. It exists to orient the ball joint and define the last bone's
  length. It will not be in the bind.

This week

References

• Everything you thought you knew about Maya Joint Orient is wrong! — Rigging Dojo — assigned reading. The best single article on this topic.
• Maya Help — Orient Joint Options
• Maya Help — Orient a joint's local axes automatically
• Maya Help — Orient a joint's local axes manually
• Maya: Rig Joint Orientation — Create 3d Characters
• #RiggingInMaya Part 04 — Rotational Axes & Orientations

Next: Week 4 — Skeletons II · Unit 2 Overview