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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 ?

Doctor Famine
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1 Answers1

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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).

moonboots
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  • 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. – Nathan Dec 19 '22 at 15:34
  • sure, I meant when you're in front – moonboots Dec 19 '22 at 15:38
  • 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. – Doctor Famine Dec 19 '22 at 15:42
  • @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 ? – Doctor Famine Dec 19 '22 at 15:48
  • You need to bend the knee a bit forward in Edit mode, see my edit (or maybe I misunderstand what Nathan means) – moonboots Dec 19 '22 at 15:49
  • Either mode works. Edit mode means it will persist through clear rotation operations, but you'll be editing your bones' rest positions, which may be undesirable. Sorry I can't give you many details now, am stuck on mobile for a while. – Nathan Dec 19 '22 at 15:56
  • Well, I understand what you're saying but it still does nothing to solve the issue. I've tried to bend the knee in edit mode, same behavior. In pose mode (less convenient), same behavior. I even tried to make my pole target part of another armature (because you never know), same behavior. So puzzling… – Doctor Famine Dec 19 '22 at 16:03
  • Could you please check the file I've linked. If it doesn't satisfy you, you should keep the legs vertical, not spread – moonboots Dec 19 '22 at 16:06
  • Sorry but which file ? – Doctor Famine Dec 19 '22 at 16:08
  • In my answer.......... – moonboots Dec 19 '22 at 16:09
  • (Sorry, hadn't refreshed the page :/) And well it does satisfy me, absolutely ! Do you what you did that I failed to do ? Because i'm gonna have to do it on the rest of the body so I'd like to be sure rather than bother the internet in one elbow. – Doctor Famine Dec 19 '22 at 16:17
  • I haven't done anything more than what I say in the answer, but as I say, maybe you should use a more vertical pose for the legs, like in the videos – moonboots Dec 19 '22 at 16:25
  • Let us continue this discussion in chat. – Doctor Famine Dec 19 '22 at 16:34