Sorry to repost this here I posted this on odforce

Im starting to use kinefx for rigging.

I setup a ikchain sop of 3 bones but as soon as I start moving the tip bone with rigpose

the ikchain quickly exhibits gimble lock popping when the tip bone gets close to the mid bone.

As a result the bonedeform twists the mesh into a ugly mess.

Are there any links to helpful tutorials that show how to resolve this?

Here is a link to a movie I made to illustrate the issue

https://vimeo.com/597357875 [vimeo.com]

this is not gimbal lock, it just seems like your IK twist effector is right around the leg knee
usually you want to have it further away, since that's the location where the knee will point towards
so if your paw is in front of it your knee twists to look back at it, etc

Hi Tamte,

So are you saying the root of the twist effector bone should be closer to the paw in the rest skeleton?
I'll try that but it looks like classic gimble lock rotation popping to me.

no, what I meant that the points you are using as twist effectors are probably copied from knees
ideally they'd be offset way forward so that the actual knees can point towards them even when you move ik goal forward

WillA
I'll try that but it looks like classic gimble lock rotation popping to me.

the gimbal lock is an issue from animating usng euler angles that comes from the nature of euler axes being evaluated hierarchicaly and therefore in some configurations you are likely to lose degrees of freedom, most likely encountered in FK animations when using all 3 axes
IK is not updating bone rotations using euler angles but rather matrices or quaternions
while IK is a stable solve, the flipping seems to be coming just from incorrect position of your twist effectors

Thanks for the more detailed explanation.
I wish there was a tutorial out there that focused on this rigging issue because I tried to move the knee bone a bit and it did help but the popping mesh deform still happens a lot. A frustrating issue that even happens with the sofie hda that I got from the sidefx demo area.
I'm surprised that there aren't lots of rigging artists complaining about the issue.

I don't think it's normally an issue, it's how 2 bone IK solvers generally work independently of software so nothing much to complain about there
you can parent twist effector to IK goal if you prefer, but a lot of times its parented to hips and just animated independently
the point is to always be mindful of the position of the twist effector since knee will always tend to point towards it

aaaand look at that, simple search returns Matt's video that seems to exactly focus and explain the issue you may be running into
https://www.youtube.com/watch?v=ZEFYdbhsVi0 [www.youtube.com]

Tomas thank you so much for pointing me to Matt's video. I think its right on the mark and I will try to replicate his final sop network. Doing so will teach me more houdini which I want anyway but I wish there was a built-in one sop implementation that did it Matt's way for me.

BTW the issue is also addressed in Parker Coleman's post here
https://youtu.be/OHeo6d-gHfI [youtu.be]
you use rigpose to offset the mid bone enough to stop the flip when the goal bone gets too close to the mid bone

but it would be nice if somebody at sidefx added "fix the flip" toggle to ikchains so I don't have to manually do all that's required to fix the issue

WillA
but it would be nice if somebody at sidefx added "fix the flip" toggle to ikchains so I don't have to manually do all that's required to fix the issue

that's mostly about understanding how 2 bone IK works, you simply have to define the 2d plane in which the bone bends somehow
traditionally it's defined using twist effector or pole vector or ehatever you want to call it
it's one of the possible controls that animator can use to tweak it and of course it's position matter
and it's up to rigger to implement automatic solution if desired since it always involves certain assumptions about what the direction of the knee depends on in a particular rig or component
because inherently there is infinite solutions for knee direction so you have to provide hint one way or the another

also kinefx is a framework, currently mostly composed of low to mid level utility nodes, not necessarily high level rig components, to build those you combine in any way you seem fit as a rigger, for example like Matt's setup and then package into HDA to build higher level components or full rigs
but of course it's very likely that in time sidefx will also provide more higher level nodes examples and tutorials as the framework grows

Hi Tomas,

Thanks for your in-depth explanation of how 2 bone ik works.
The more I understand the better.
I have put in a rfe for this issue so hopefully sidefx will add some options to ikchains that will
prevent other artists from having to invest a significant amount of time to resolve a gliche like this.