IK Snaps back to home position

Ok. I have performed the rigging and animation examples from “The Essential Blender” and got Hank fully rigged and functional.

I have a problem when I try my own mesh and rigging though. Here are the details:

  1. I have 5 bones, all extruded from the first, in a straight line along the Z-axis.

  2. I select the last one and hit [Ctrl]+I to create my IK Solver constraint and then select “Without Target”.

  3. The chain moves well enough, but when I move the mouse so that the Head of the very last bone, the one with the IK Constraint, approaches the Z coordinate of the head’s original position, the whole chain snaps back to the original position. Also, if I choose “A New Empty Object” instead of “Without Target”, the problem persists, even though I have a bit more control.

I need this chain to be able to cross that line without snapping the way it does.

I do not know what is going on, but I do know I can not get the animation to work if this chain can not cross that Z line.

P.S. I have just found out through some experiments that if I place the bones in a non-linear orientation, my IK works the way I need it to, but if I place the bones in a straight line, they snap when crossing the line that the bones are laid on.

So I guess my only question now would be What if I need to place an armatures rest position in a straight line and not get that crumby line-cross snap effect?

That’s just how IK works … usually you need to give the IK a direction by putting in a slight bend in the joints for the IK to behave predictably … or lock some IK rotations for some bones … But for such a long chain in a straight line up will almost always give you that snapping …

What are you trying to do with this set up anyway ? You might be better off using a curve or a lattice instead …

Yep. You need to build a tiny amount of curvature into your chains to give the solver something to work with.

I see. That is easy enough. I am modeling and rigging a leopard’s tail that needs a good bit of flexibility, but will be used to grab hold and force other objects, so I need it to be posable and relatively easy to animate.