wierd motion from rigged character!!help!

hi all, I am following the book “Introducing Character Animation with Blender” by Tony Mullen. I am in chapter 4 (Armatures and Rigging), but i am kinda stuck at the spine IK solver. It seems that it makes it move erratically when i try to just move it a little bit. not only that, but if i right-click (or escape) the armature doesn’t go back to the rest position, but it take a strange position. the problem is on the bone “IK_spine” (I believe), between “shoulders” and “upperbody.”
i don’t know if i am doing something wrong (most likely) or something is missing in the book. the blend file is in the following link:


Thank you for you help.

PS. I changed the links to reflect the correct blend file. sorry for the confusion.

You don’t have an IK solver in your blend or for that matter a “IK_spine” bone/target … but it sounds to me like you might have cyclic dependencies in your set up . This is usually cause by the target being a part of the parenting hierarchy when it should be independent of the chain it is the target of . Tab into Edit Mode and check to see if this is case … or use the Outliner .

I can’t be any more specific without a blend that has an IK solver in it … Maybe Tony Mullen aka Bugman_2000 will know …

thanx for the quick reply Vertex Pusher.
well, yeah, “IK_spine” bone is extruded from the “spine.4” bone (the top spine). But that was how Tony Mullen explained it in his book in the following paragraph:

       "Next, you will add the IK solver for the spine. <i>You can extrude this straight up out of spine.4 </i>in Edit mode, as shown in Figure 4.43. You must reparent it because spine.4 will be in the IK chain. Name the Bone <b>IK_spine</b> and parent it to shoulders. In pose mode, add an IK constraint  on Spine.4 targeted to IK_spine." (page 157, last paragraph)(the underlining is mine)

I did exactly as he explained. but i think the trick is in the reparenting part. Maybe i should “connect” IK_spine to shoulders instead of “keep offset.”
I hope that’s what Tony meant by “reparent” because until now, we have been only using the “keep offset” option.
I am at work now, and i can’t download the .blend file from the first post for some odd reason.
I’ll check at home tonight, and i’ll keep you posted.
thanx for the help

hi again,
sorry for putting the wrong .blend file. here is the right one:


also, in the previous post i thought that using “connect” type of parenting will solve the problem, but it didn’t. I also checked the book again, and i found on page 178 that “IK_spine” shouldn’t be connected to “shoulders.” So, i got no clue what it is.


Well the problem is exactly what I thought it was . You do have a cyclic dependency because right now the shoulder bone is the child of spine.4 and you have the the IK_spine as the child of that .

To fix this just unparent the IK_spine bone from the shoulder bone . And (I am not sure if Tony’s book does this - I have not read it - but this will work just as well) parent the the IK_spine bone to either the root bone or the torso bone or the pelvis bone . All three are at the same hierarchy level as the spine.1 bone and outside the chain of the spine.1 bone and shouldn’t cause any problems .

And speaking of hierarchies, you need to make the torso,pelvis, and spine.1 bones the children of the root bone . This way you just have to move the root bone to move the entire armature in Pose Mode …

Also you want to turn the Rot option off in your IK solver, otherwise your L/R shoulder bones will rotate erratically .
And turn off Auto IK - with this on you can only rotate the bones even if they are not connected .

Good luck

Thanx alot Vertex Pusher,
I re-made the rig from scratch and made sure i read every letter in the book, and it turned out i didn’t have that problem. but your explanation makes me understand it and avoid it in the future.

for the “Rot” option, Tony wants it to be applied. The reason i believe is that when it not applied and you rotate the “shoulders” bone the shoulders (L/R) don’t rotate with it, but if you rotate spine.4 they do rotate with it. (strangely enough). Again, i am no expert, but that’s what i got from not having the “Rot” option applied.

again, correct me if i am wrong.
and thanx a lot again, i have a clearer idea of hierarchy in rigging.