From BlenderWiki

[edit] The B-Bone Spine

This is probably the easiest way to make something curvy and animated. B-Bones have to be perfectly in line with both the parent and child bones in order to be straight in rest position.

Segmented B-Bones are best used for cartoon-like characters, because b-bones change length as bend angle increases.

You should never change the scale length of a bent, segmented b-bone. If you do, it will sheer the bone segments and thus sheer the area of the mesh those deforms. Of course, you can do this if that's the effect you want.

B-bones are very useful in rigs to do things such as twisting. If you set the blend-in and blend-out values to 0, it will cause the bone to remain completely straight, but still twist.

As you can see in the image on the left, the last segment is never quite as far rotated as the child bone. For this reason, it is sometimes a good idea to have an extra bone after the segmented bone.

In the last image of this sequence, you see a small green bone. It's copying the local rotation of its parent, which is why the b-bone is arched nicely in that image and not in the second image. The arms and neck are children of the green bone. If you parent them to the b-bone, they won't have the orientation of the last segment of the b-bone, and will be as they are in the second image.

[edit] This Rig in Review

Now lets consider the benefits and drawbacks of this design.

[edit] The Pros

• Way easy to use.
• Very useful for twisty areas, like human forearms and upperarms.

[edit] The Cons

• B-Bones change length when bending and are therefore, not a good choice for realistic character spines.
• Input is limited to two rotations and so the possible curvatures are limited.
• Movement is unnatural because the segments stretch to reach around the rotation points. It's more like a slinky than a spine.

--Wavez 08:34, 17 July 2006 (CEST)

Redirects to fix

• BSoD/Introduction to Rigging/Spine Rigs → Doc:Tutorials/Animation/Armatures/BSoD/Spine Rigs
• BSoD/Introduction to Rigging/The Propagating Rotations Spine → Doc:Tutorials/Animation/Armatures/BSoD/The Propagating Rotations Spine
• Blender Summer of Documentation → BSoD
• Manual/Manual → Manual