What are IK Bones?
An "IK bone" is a bone that acts as a "grab" bone, that can grab a tip of a chain and move it around.
In older versions of blender (pre 2.40) the IK bone could only grab hold of the end part of the bone. This required creating an null bone which did nothing other than provide an end for the IK bone to attach to.
In a newer version of blender (2.40+) you can enable the "Use Tip" button and the null bone is no longer required:
BUT, if you are going to continue using the null bone, you must disable the "Use Tip" button.
How to create a chain of bones?
Here is a chain of bones
But they are not a chain yet... You need to parent them to each other.
So click on Bone.003 and make it a child of Bone.002.
Also enable "Co" to connet the bone to parent.
Repeat the step to all other Bones.
Now create another Bone at the start of the chain, Call it IK. This Bone will act as our IK bone.
Bone.003 is our "IK Solver" our tip of the chain, and is the bone that the IK bone will grab.
In Pose Mode, click on IK Bone, followed by Shift clicking on Bone.003.
- Click Ctrl+i (this is our shortcut key that will automatically make Bone.003 as the "IK solver" and the IK bone as the "IK bone.")
NEW step, required in 2.40+
In the newer version of blender, you must tell the "IK Solver" Bone where the chain ends. This is defined in the ChainLength field:
If the value is left at zero, Blender will assume that all bones that are parented to each other are part of the chain. So for example if we parent a chain of finger bones to a hand bone, blender will assume that the hand and the finger are part of the same chain, and when you move the IK bone around pretty much the whole armature will move.
