View Full Version : Hybrid spine

08 August 2008, 03:08 PM
Hi guys.
I'm trying to figure out, how to make a spine for a bipedal character, which will be a hybrid between Spline IK and FK.

My theory was this:
Make a Spine with any number of joints (I think it was six, but it's not that important)
Copy the spine, so I have two of the same.
Spine 1 would be SPLINE_spine
Spine 2 would be BOUND_spine

SPLINE_spine will be setup with a Spline IK solver, and clusters are created at the control points of the curve that the spline IK solver generates.

BOUND_spine will be setup as a regular FK spine system. It has control objects placed at every joint, and bones a orient constrainted to the control objects.

Now I would Point constraint the BOUND_spine joints to the SPLINE_spine joints, so they get their Spline IK abilities, but it should still remain the orientation constraints from the original setup.
Unfortunatly they can now no longer be rotated, it's like it's overruled.
It seems logic okay, because if it did rotate, they would no longer be placed at the same position as the SPLINE_spine, and they are forced to do so, by the point contraint.


Okay, does anybody know how to make such a hybrid system? The reason is, that I don't like to animate with translation, so I would prefer to rotate my spine, to get the desired pose. But Spline IK systems just have a great amount of freedom, and it's so easy to get the exact pose I wan't.
The ANDY Rig has that functionality btw.



08 August 2008, 07:02 PM
Hello Denmark! :)

Im working on something like what you might be intersted in right now, I wrote this yesterday in another thread:

"Ive been working all day with a new solution and have found a good solution, kind of a combined IK/FK spline. Nothing revolutionary of course, but now it works much better. Heres a short describsion:

I have my 8-joints-splined-chain and then a 4 joint "FK-chain" working together. Then a locator at the origo that is parented under the FK-chain, so it inherits the FK-chains movement. Then the locator is the driver(parent constrain) to the chest-controller of the spline-chain. That mean that when I rotate or move a joint on the FK-chain, the chest-controller moves with it = the FK-chain drives the spline. "


If you want, I can send you a scene-file so you can have a look yourself if Im doing what you are after

// Otto

08 August 2008, 07:12 PM
Hey Sweden!
It sounds just like that!
I'd love to see the file if you'd be so kind :)


08 August 2008, 08:11 PM
Here you go

On the globalControll(COG, the ring with arrows to the sides) there is an attribute to switch between FK & IK on the spline. Some pretty cool results can be created by moving both the FK and IK controllers on the spline.

Tell me what you think, would be cool to develop this setup more. Im sure it could be done. You are of course free to test new things on this file, just upload your version later :)

// Otto

08 August 2008, 09:11 PM
Hi Leffler
Thanks a lot for your file.
It always really nice to see how other people rigs :)

I think I managed to get kinda what I want, though.
Take a look if you want. You can download it from this link:
Link (

I'm really sorry for the lack of naming, but it just threw it together.
Basically I parent constrainted the upper cluster to the circle closest to it.
That way, it will still let me rotate.
Then I just point constrainted my bound bones to the spline bones.

Anyways, take a look at it, and feel free to edit/change stuff, if you feel like improveing upon it.

The joint in the buttom is not supposed to be bound to anything. It's just for selection purposes. Imagine the joint above it, being the pelvis, then going into the abs, the lower ribcage, the upper ribcage and then the neck and head.
That should give you some idea of what I was aiming for, when I created them.
I didn't draw so many joints for the spline, as I only need the spline control around the abs, but obviously I could have continiued on to the top :)


08 August 2008, 06:21 PM
Looks good!

The thing I would be most concerend about is that if your translate the lower circles the joints and the controller will separate alot. This can be really weird when animating I have found, but its more a "spline-ik" problem then a problem with your setup. Adding stretching to the spline can help it

I think the best way to troubleshoot this setup would be to apply it to a character. Then you can see how much of a problem it will be that the circles end up inside the stomach and separate from the joints.

Im going to bind my setup to a character tomorrow so Ill se what happends to my setup aswell, would be cool to stay in touch and see what happends with our setups when deforming mesh

// Otto

08 August 2008, 01:10 PM
Yes, it's a really big problem, that the controler and the joint are not forced together at all time. They should be.
Don't know how to solve it though, but I'll keep working on it :)

And yeah, would be nice with a solution, so please let me know if you find one, I'll do the same of course.

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