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I'm trying to rig a humanoid low poly character in Blender 2.82, starting with its legs. For this, I've been following two different tutorials on YouTube but they fail me at the same point :

Rig ANY Character for Animation - Easy Character Rigging with IK

Everything is going well up until I try to set the pole target. At first, there's this pole angle issue when I first select the knee pole bone. The leg is not facing the pole target but I understand that I can fix this by changing either the pole angle in the IK constraint window or changing the roll angle of the bone in edit mode so its x-axis is facing the pole bone. OK. But once this has been fixed, the whole leg behave weirdly, meaning it doesn't bend on the hips/heel/knee plane but rather unrestricted while it's not the case in the tutorials.

I sense I'm not far from the answer, just missing some key elements. You can download the blender file here.

EDIT : I tried to align the bones in my leg like moonboots suggested but it doesn't change a thing. Am I looking for some magic spot that makes everything go like it should ?

I'm not even sure I'm trying to solve an existing problem so let me be clearer : the issue is that I would like to lock the bending of the leg on a plane. You can see on the video here that I've modeled a blue triangle which has each of its angles on the knee, ankle and pole target resting positions. You can also see that when I bend the leg, it goes haywire, not staying on that plane at all.

Am I trying to solve something solvable ? Is solution still resting in the alignment of the leg bones ?

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I think that the straighter your bones will be the better it will work (in Front view). Now don't ask me the mathematical explanation :/

enter image description here

As Nathan says, you need to keep it bent forward though:

enter image description here

Link to the file: https://workupload.com/file/79qVuagYDbv

Of course you'll need to move the pole targets to adjust the knee direction. It may be more convenient to choose a pose with vertical legs (they are almost vertical in the video while they are rather spread in your case).

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  • $\begingroup$ Yes, up to a point. Perfectly straight is undesirable. The bones will bend in the direction the currently bend. If that includes X+Z rotation, they will rotate in X+Z. If it is only Z rotation, they will rotate only in Z. If it is perfectly straight, it will be undefined, and the leg probably won't work right. It is the pre-IK posed bend that matters, not the rest bend, but building the bend into rest is usually most convenient. $\endgroup$
    – Nathan
    Dec 19, 2022 at 15:34
  • $\begingroup$ sure, I meant when you're in front $\endgroup$
    – moonboots
    Dec 19, 2022 at 15:38
  • $\begingroup$ I tried. Not a success. I've edited my question accordingly. Although, I just saw your comment, @Nathan and haven't tried with this new knowledge in mind. $\endgroup$ Dec 19, 2022 at 15:42
  • $\begingroup$ @Nathan, do you mean that I should bend the leg a bit in pose mode before setting the IK and not do it prior to that in edit mode ? $\endgroup$ Dec 19, 2022 at 15:48
  • $\begingroup$ You need to bend the knee a bit forward in Edit mode, see my edit (or maybe I misunderstand what Nathan means) $\endgroup$
    – moonboots
    Dec 19, 2022 at 15:49

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