I know you can assign CP's to bones but can you use an expression to make a CP always stay at the base of a NULL???
If so I would appreciate an explanation of how to do it please.

how about if you just constrained the bone that the CP is on to a null?

That is what I ended up trying.
I was hoping to be a little cleaner and save the extra bones but it works.

Thanks,

Large numbers of bones don't seem to be a big memory or render time problem. Probably faster than an expression.

Well, if you want it a *little* cleaner, just make the bone a child of the null (instead of placing a constraint on it).


Martin told me once that expressions are very expensive operations. Testing with large numbers of models in a chor, this does appear to be true. Although I don't notice much of a slow down with only one or two models (which have expressions in them).

What this is all for is an idea I had awhile back to make a stretchy spine that was constrained to a path.
I've seen reference to it in a couple books "Character Animation in Depth" that Robert suggested a long time back and "Body Language" which is more oriented towards Maya but the ideas are good.

I've struggled with the spines in some of the available rigs.
They are great rigs but the spines just don't work the way I think I want them to.
I may end up learning why they left so much of the articulation to be weighted and manually adjusted but I wanted to try to reduce my pain.
I am also trying to make the articulation completely separated from the geometry bones.
Basically so the geom bones can be simply "oriented like" the underlying rig but have zero affect on the controls.

Thanks for the help as always,

Here is what it looks like so far.

Click to view attachment

Can you say more of what you mean by that?

The spine I am most familiar with used three bones.
One was the chest and two were the lower stomach area.
With only three bones I had to do a lot of weighting of CP's between the two bones in the stomach, or, I had to find ways to constrain a fan bone between the two stomach area bones.
The rig works and is certainly a great rig.
I just wanted to make a spine that had bones that blended the twisting rather than quite so much weighting of the CP's.

I'm new at rigging so this may be a complete wrong approach.
I'm just trying and learning.

I don't want you to stop experimenting with rigging, because it never hurts to understand that more.

None-the-less, the TSM2 spine is five bones, is stretchable and behaves much like you are describing.

I agree the TSM2 rig is the one that does do pretty much what I am looking for.
I purchased it before it was free.
A lot of this is for me to understand rigging.

I get frustrated when I want a rig to have a little different articulation and can't figure out how it is built enough to try altering it.
I figure if I build my own simple rig, maybe I'll learn enough to understand rigs like the TSM2.
Then I won't be so locked in to what others have done.

Yessir.

I'll second that