I’ve got a nice little low-poly mesh associated with an armature just the way I want. I went in to add IK to the legs, but when I add the pole target in, the knees bend the wrong way. If I change the pole angle 180 degrees, the knee bends correctly, but the mesh leg points the wrong way.
I’ve been tabbing in and out trying to figure out the combination of roll and pole angle that will work, but nothing works.
All I can think if is that I had stuff rotated wrong when I associated the vertices, as if I made my armature “backwards” and then the verts got glued to the reverse side. Is there something I can turn on to see what the “front” of a bone is? It seems odd that I couldn’t reset the association of which “side” of the bone the verts are on.
My guess is that you’ve run in a common issue with IK.
You need to give the leg an initial rotation, in edit mode move the joint a little bit toward the knee, so the two bones are not completely straight. And remove the 180° pole angle.
Watch most of the tutorials on IK if you want to understand better the issue.
Sometime you need to set the pole target value other than 0, but my guess here is that the legs bend the wrong way in the first place, setting the pole target give the correct bending, but then the leg is twisted.
When you create vertex groups there is no notion of rotation. The Rest Pose is corresponding to the armature in edit mode.
When you’ve got these kind of flipping it means that the issue is in constraints, or everything that append out of edit mode ( pose mode) …
Well this mostly solved it, I’m good to go. I don’t think I noticed this anywhere in the docs, that’s been how I’ve mostly been getting by so far (without much issue). Anyway, thanks!
However, there’s some weird behavior:
I killed the relationship to the armature and then went in and set every bone to 0 rotation. Then I re-did the parenting, vertex group weights, etc, and used the “slight bend”. Hunky-dory, except when I set the pole target, it rotated everything 90 degrees. The target was directly in front of the knee. Any idea what might have caused this?
Ok ! then you probably need to set angle in the pole constraint.
try rounded values like 90, -90 , 180 generally it works…
TBH I don’t know why it’s needed but it works !
And for the IK slight bend, maybe they don’t speak about it in the docs, I think it can work sometime if you’re lucky … in some ways if your character was modeled the other way around, then you wouldn’t notice any issue.
But clearly it’s common with IK, in different softwares… You can see the issue in action here :
It’s not the best example but that can help you giving you an idea !
If the chain is straight without any bend at all it’s worse because the IK really don’t know where to bend. But yeah, that can work but it makes it really unpredictable.
