# driving shapes

Is it possible to add a bone driver to a shape being the bone within an IK chain?

I can set a driver if I actually move the driver with the mouse like a slider or any FK chain. But I need to drive a shape by the rotation of a bone which moves only by its IK, no direct manipulation. Since bone’s withing IK don’t see to change theirs transformations then the shape is never driven.

### Attachments

Use a seperate bone with a copy rotation set to the bone in the ik chain.

However it does not work either. It seems that any bone moved by a constraint( IK, copy rotation, copy transform etc ) can’t be used as a driver. The copy rotation have the same effect ( its X, Y and Z transformation values remain on zero when the bone is moved by a constraint. It seems only to work if you pose the bone manually. There must be some sort of copy rotation from visual transform. We had the same restriction on 2.49b, but I was used to get a work around using an external bone as a child. But in 2.5 neither the child can drive a shape.

In theory, in 2.5x you should be able to set up a “Rotational Difference” variable to get around the problem of drivers ignoring constraints. It uses the angle between two bones (in radians) as input to the driver. If you still need help tomorrow I can set something up quick to demonstrate, but I do not have access to 2.5x at the moment.

Here’s an example Blend using rotational difference, this works even with IK as CD38 has suggested.

### Attachments

driver_test.blend (517 KB)

@ CD38 and Pappy:

Thanks so much guys for your answer , that’s definetly a beautiful solution. It is amazingly clever and useful the implementation of rotational difference, since you may need a pose where shin stays straight but thigh isn’t so the shape would still work. This won’t be the case if we had a shape driven by only the shin’s Rotation.

Pappy: Thanks for talking the time in creating this setup file.

3Dmentia: Thanks for your answer, that was my second thought of creating a copy rotation, then a child of, blocking its copy position. Never played with rotational difference, I thought it would be the same problem. :no:

@pappy very nice demo, that’s what I’m talking about.

You can thank Aligorith for his hard work on this and recoding in general the animation system. Hope this solution works for you.

Thread closed. You have been banned Nimotop, as Animaticoide.