IK Constraint: Bone Becomes Detached

'Hoy there, guys.

I’m having issues with IK in Blender at the moment. I’ve got a rig like so:

The numbers correspond to an IK constraint, with Yellow being the bones it’s applied to, and Red being the bones that are the target of said constraint. The IK on 3 has a Chain Length of 3 so that it applies to the entire leg, while the other two are only set at 1 so that I can use the Red bones to control which direction the joints go.

The issue I’m having is that, when 2’s IK Constraint is active, it stops attaching to 3 and goes completely off, just so:


Any idea what’s causing that? It doesn’t usually happen with this rig.

Here’s the file, if that’ll help:

Checked out your file. Nothing terribly wrong with but - there’s no IK on any bones but ankle.r and ankle.l, and the thigh bones really should have their locations locked because it’s possible to pull them away from the torso. That’s gotta hurt. similar problem for the jaw.

That’s… Odd. I must’ve made a mistake and somehow uploaded an earlier version before I had that set up. Huh. Here’s a better one:

I’m not sure what you mean by locking the location. I typically only use the Rotate tool when doing poses, and the IK stuff doesn’t move the thighs from their position, so them moving away doesn’t usually happen.

Well I’m not sure if I actually have an answer as such… One of your chain inside a chain IK constraints was clearly substituting for a pole target, so that was fairly simple to fix for both legs.

The shin was part of an IK chain but also had an IK constraint on it. So it was in a 3 bone chain, and in its own 1 bone chain, and its allegiance was divided. People do use this kind of rig but I have negative feelings about its usefulness… And when it comes to chain in chain in chain …! Rather than preach about it I decided to completely f-- up your rig to teach you never to do it again. Just kidding!!

What I actually did was rig the right side in a ‘safe’ way, with no chain inside a chain, and using a pole target. The left side has a chain in chain construction that is probably the way most riggers who use this construction would rig it. The advantage is slight and the animation is often unpredictable. Learning to use the rotation limits and stiffness settings in the IK panel in bone properties is a better way to get the same result IMO.

Anyway I hope this helps you along rather than just being a lot of hot air!


PS I hid all the other stuff, so you’ll have to unhide the other bones in pose mode and then in object mode unhide everything else…

Niiice; that’s quite useful. Thanks for the assistance! I suppose I’ll have to avoid Chainception in the future. At least for triple-jointed rigs.