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[edit] The Bend-O-Matic Spine

"Bend-O-Matic Spine" is just a term given by this author to one of his rig designs. This design should work for most athletic human-type characters, but it's probably not quite adequate for some other types of characters, such as a contortionist. This rig should also work well for making a dancer, because this rig has two controls for hip movement that cause the spine to bend, and the upper body to stay relatively still. The control that causes the spine to arch also induces twist as well.

Keep in mind that this particular example is designed specificly for use as a human-like spine, but you could produce many different types of variations on this rig for lots of different uses.

[edit] Lets Build It

Start out with a single bone placed near the center of the first disc extending vertically to the disc between L1 and L2. You want the bone to be perfectly vertical. From this bone, we will create all the deform bones for this rig. Subdivide it twice. Name the bones spine1 through spine4, starting at the base. Duplicate spine3 and spine4, and move them up to the end of the chain, and name them spine5 and spine6. Make spine5 a child of spine4, connected (for now). Those are all the deform bones for this rig. Add a new bone at the center of spine6, and name it torso. Now select all of the spine bones, duplicate them, and translate them on the Z axis to the end of the chain. These don't need good names, but if you want to name them anyway, I would suggest using spineIK1 through spineIK6. Make each one of these a child of torso.

IK constrain each spine bone to it's spineIK duplicate. Change the ChainLen value to 1 after each constraint is added. Now rotate torso in pose mode and watch her go!

[edit] "But my spine is curved!"

The spine is probably useable as it is now, but if you want to give it more of a curve like a human spine, then we need to move the bones. We could move the points of the spine to make it match the arch in the image, but if we do that, our bones won't point straight up, and that means they won't be pointing at our IK targets. We could try moving the targets, but then the arch backwards or forwards will change.

Instead, disconnect all of the bones. Select spine2 and it's target bone, and move them both until spine2 sits about where the center of the disc between L4 and L5 should be. You shouldn't have to move the bone up or down very much to make this adjustment, and the less you do, the better. Now do this with the rest of the bones and IK target pairs, for each corresponding disc of the spine. You should also move the torso bone forward 0.1 or 0.2 Blender units. Doing this changes the shape of the arch, so you might want to do a test:

• • Rotate the torso bone forward in pose mode.
  • Create a duplicate of the armature.
  • Change the position of the torso bone in edit mode for this new armature.
  • Reenter pose mode to see the difference between the two arches.

The more that you offset the bones from the originally vertical column, the more effect it will have on the arch that the spine forms when it bends, but arranging the joints this way makes it easier to do even more tweaking of the arch. Here's another experiment to try:

• Rotate the torso bone forward in pose mode.
• Select any of the target bones and translate them on local Y.
• If you decide you want to keep some changes made to the target locations, then make the same changes to edit mode and clear the locations in pose mode.

[edit] Let's Make it Do the Twist

I've been told that twisting of the human torso occurs near the middle of the spine (T11 and T12) and not at the bottom (L1 through L5, or the lumbar region). Whether or not you want your rig to be as anatomically correct as possible is completely up to you. You can make the spine twist at any bone you choose. You can also use the torso bone as the target of the rotation constraints. For more in-depth info, please see the page titled, Making A Spine Twist.

What you decide to do should be your own decision, based on your own experiments, and what you think works best for your character.

[edit] Adding the Hips

What we have made so far is a good rig on it's own, but we can do a little more to make it even better. We can add extra pivot points to make for easy and quick-to-animate hip movements. These extra pivot points go in as additional hierarchy levels between the spine and the body bone.

Duplicate torso, resize to 50%, and name "bender". Duplicate bender and move it straight up (constrained to Z) about 1.5 units and name it something like "benderIK". IK constrain bender to benderIK, and set ChainLen to 1. Add a new bone, "hip", and place it over the leg ball sockets in the image. Add and place a new bone, "shaker", half way between hip and torso. Setup the hierarchy like so:

• body
  • benderIK
  • shaker
    • hip
      • bender
        • torso
      • spine1
        • spine2
          • spine3
            • spine4
              • spine5
                • spine6

[edit] Locking Things Up

Final steps: Lock the appropriate axes of the bones, and organize your layers.

[edit] This Rig in Review

Now lets consider the benefits and drawbacks of this design.

[edit] The Pros

• Creates great hip and torso rotation that is very quick and easy to use.
• Induces twisting, not just bending.
• Allows for additional arch shapes during animation by translating or scaling the torso bone.
• Allows for some hip movement while the upper body stays relatively motionless.

[edit] The Cons

• Slightly lengthy setup period.
• Works well for bending, but can't do wavy movements.

--Wavez 14:37, 30 June 2006 (CEST)

Redirects to fix

• BSoD/Introduction to Rigging/Making A Spine Twist → BSoD/Introduction to Rigging/Making a Spine Twist
• BSoD/Introduction to Rigging/The Bones-on-Curve Spine → Doc:Tutorials/Animation/Armatures/BSoD/The Bones-on-Curve Spine
• 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