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Spine Hip Issue

Hi! It has brought to my attention some sort of misbehaviour regarding spine components.

As you can see in the video, the hip rotation affects the upper part of the spine badly ONLY when the FK controls are not at 0. Is this due to a spine IK limitation or a bug?


Unhide the components of the spine (spine_C0_mst_crv), and you’ll see it is a matter of order of operation.

When you rotate the FK controls, you are rotating the joints away from the tangent of the spine. The FK is the child of the IK.

spine_FK_01 has the IK as the child of the FK.

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Thank you, Chris!

I’m struggling with this exact problem, as an animator I want to give movement to the hip and don’t affect the movement in the upper body, specially the shoulder/neck area.

I’ve switched my rig to FK spine component, but even so, there is movement on the top when you use the hip control.

on the gif, ignore the Translation movement, my problem is with the rotation of the last spine joint.

I expect the hip control to be separate from the spine, like the clip bellow. and I think this is what @Milio was looking for too ?

maybe I doing something wrong, like grabbing the wrong control, or having the wrong guide settings?

Hi @Gui I don’t think so. I think you are describing a different problem.

There is no “hip control” in the spine_FK_01 component or the spine_IK_01 component.

If I’m not mistaken, I think you are moving “spine_C0_ik0_ctl”, right? This is the lower IK tangent control of the spine. It has nothing to do with “hips”.

If you want hips, make a hip control! What I do is use control_01 and I make a “hips” and “chest” controller. The hips control parents everything below the spine. The chest control parents everything above the spine. And I use them as offset controls that don’t affect the spine at all.


aaaah, this makes sense! I was indeed grabbing the spine_C0_ik0_ctl, I always thought this was inteended to be used as a isolated hip control - Thanks for correcting that.

haha, I’ll do that!

Thanks again @chrislesage :smiley:


haha good! I suspect some people tend to feel a bit restricted by the biped template. I see it as a very basic starting point. :slight_smile:

yeah, specially when making a game rig I don’t want to add unnecessary number of joints.

Sorry to go on a tangent here from this “bug report”, but do you create a joint with your hips_C0_root and chest_C0_root (control_01)?

do you create a joint with your hips_C0_root and chest_C0_root

Yes I do, and I use them to skin as well. And skinning the chest can help with some of that stability when the top spine joint may scale or rotate in a bad way.

Also, if you are working in Unity, where you may have scaling/skewing problems, you then have the choice to parent the hip/chest joints under the root joint, and avoid the scaling of the spine joints. (Though it gives you a broken hierarchy, which is not always wanted.)


yeah that makes sense, I just tried it works so much better!
I assume you put the hips on the same location as the COG, and the chest on the same as the last spine, correct?

Yes to the chest. No to the hips. I put the hips under the spine root. Otherwise if you move the spine, the hips don’t follow, and you end up with a useless spine control.

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