Character rigging-The essential blender

I am working my way through this book and things have been good so far. Now at chapter 7 (rigging and skinning), I am stuck. :frowning:

After making the legs into IK chains things are alright (pg 163). Then the next section - Adding a locktrack constraint for the knee. I have done this section a number of times with the same result. After returning to pose mode, I find the bones are all in a mess. I return to edit mode they are as they should be. Back to pose mode, they are a mess. :(:frowning:

What is going on? Any help would be wonderfully appreciated.

In pose mode select all the bones with A and hit alt+g then alt+r. This should sent the bones into their original position

Thanks. I’ll try that.

or hit w, to clear user transform and do all those in one go.

Sorry if I’m bumping a slightly older thread here, but I’m having the exact same problem. However, clearing the transforms does not work for me. Instead, I’m getting an error in the blender console window:

Cycle detected:
foot_L depends on leg.control_L through Parent Relation.
ankle_L depends on foot_L through Parent Relation.
leg.control_L depends on ankle_L through IK Constraint.

I’m using Blender 2.46, and have attached the blend file… I’ve worked through the text of the book three times with the same result every time. Any help is greatly appreciated! :slight_smile:


hank_for_rigging_2.blend (260 KB)

jabeck, your problem is with cyclic dependencies. Basically, the problem is that you have the chain length of the IK constraint for the knee set to 0 (which means infinite, so it will affect knee’s parent and the parent’s parent, etc.) I don’t know the specific cyclic dependency this creates, but in essence it means that A depends on B which depends on C which depends on A, so it is impossible to tell how any of them should move (things spaz out like you’ve seen.) You can fix it in your case by setting the knee IK chain length to 1 which is obviously what you’d want to do (actually I don’t even think you need this IK constraint.)

And just a few things to improve your leg rig, take them or leave them. First the IK constraint on the knee is unnecessary, I would remove it. Second the locked track constraint, I think, should be on the upper leg instead of the lower leg. Third, an IK pole target is clearly what you want to use instead of the locked track constraint. The pole target is made for this sort of thing (pointing joints the correct direction) and maybe the reason it is not in your tutorial is because it is relatively new. Trust me it makes it much easier to work with.

I’ve attached a blend file with the improvements I described. On the left leg, I fixed it up still using the locked track constraint, and on the right leg, I’ve used a pole target instead. Hopefully you can see how it works, it’s really not too hard.

Hope that helps!


hank_for_rigging_2_fixed.blend (263 KB)

Thanks very much - this is exactly what I needed to know. Looks like what was really throwing me off was the fact that the knee bone in the book is created by duplicating the lower.leg bone. Since it had an IK constraint to the ankle, this was also duplicated to the new knee bone (I guess a new feature since the book was written? - I noticed a few other things that the X-axis was doing for me now too that the book said it wouldn’t do, which was nice). Interestingly, this IK constraint does not get copied to the right side (created by the X-axis mirror). Seems odd to me that it doesn’t… hmmm…

Also, thanks for the tip about the pole target - It sure is nice to see blender progressing so quickly that the book authors can’t keep up :eyebrowlift: :spin: