Hello,

I have a strange issue while animating with IK, sometimes when simply moving the model, the IK snap and jump irregularly. And bones does some unwanted rotation when slightly moving them.

I've attached a file where you can see the issue described above.
just open the file, click on play… the animation is broken on the legs.

Thanks for your help

Hi there,

This is a strange happening that I don't know if I ever would have come across. The issue here is that the IK solver doesn't respond well to having an IK chain parented to a bone object directly. Please see the attached file for a comparison, there's one leg roughly matching your setup and another with a null at the root of the bone chain (which behaves as expected).

A couple of things to bear in mind… Generally I would want to keep my bones free of translates, especially in the context of a chain, so if we're going to need to translate something like the hips/COG ctrl, pass this on to a null at the root of the chain. You can see this is how houdini strongly suggests we do things, as this is what we get when we use the bones tool. When you come to deforming something that you do want to drag around that isn't part of a chain (like character props or parts of a facial rig - anything without inherent length) this is when I would say use the null-containing-capture region solution.

Also be wary of your joint alignment. The left leg is in a somewhat different plane to the right one, this can also end up in deep IK confusion later on

Sorry for the extended waffle, I hope that's of some help,

Cheers,
Henry

Thanks a lot for helping me and especially for the explanation !

I do not know all the Houdini's subtleties to make rigs and I wanted to make it with only bones (without Nulls) to export it on Unity but I guess I have to go step by step when I build the rig not to have so many issues . ^^"

Thanks again .

This was a bug in the IK solver whenever the root bone has translations. It's now fixed for tomorrow's 16.0.558 daily build.

Great stuff, thanks Edward!