🧵 Leg problem when symmetrizing in blender?
Anonymous at Fri, 4 Oct 2024 15:48:08 UTC No. 997305
I created an armature with IK and symmetrized it, then applied automatic weights and everything works as it should.
However, I cannot find a fix to this problem: as you can see on picrel, one of the legs (left leg) does not want to bend using IK, but rather becomes stiff, while the other leg has the exact same settings except it moves.
I have tweaked the settings such as the pole angle and chain length, but it doens't work.
One thing that's weird is that I tried enabling "Rotation" in the IK modifier, which makes it bend, but messes up with the leg by rotating it slightly in a shitty way, I don't know.
This is my first time rigging a character, so I'm a complete noob in that regard.
Anonymous at Fri, 4 Oct 2024 16:20:28 UTC No. 997307
>>997305
It's a long standing bug in Blender's IK solver. To work around it you need to make sure the rest pose is slightly pre-bent the right way.
Anonymous at Fri, 4 Oct 2024 16:25:53 UTC No. 997308
>>997307
mmm maya does this too. it uses the rest pose to determine the primary bending angle. if you rog your elbows or.knees perfectly strait its basically random what angle theyll bend in.
Anonymous at Fri, 4 Oct 2024 16:35:55 UTC No. 997310
>>997305
You could have asked this in one of the other threads. But anyway, it's possibly a bone roll issue. Try rolling the stiff bone 180 degrees, relative to it's current roll.
It's probably not the pre-bent thing, because if one knee is bent enough to move, then the other knee should be too when symmetrized.
So it's most likely that when the bone got symmetrized, the IK limitation went from the proper backward orientation, to an improper forward orientation, which is conflicting with the pole, causing the whole leg to remain stiff. So a 180 degree roll around should set the IK back to it's proper orientation.
Let me know if this works.
Anonymous at Fri, 4 Oct 2024 16:45:58 UTC No. 997311
>>997308
The way you make it not random is in pic related but whether that's going to work for you in default Blender it's essentially random. It's better to just pre-bend the rest pose and don't think about it too much.
Anonymous at Fri, 4 Oct 2024 16:49:41 UTC No. 997312
>>997307
>>997308
>>997310
>>997311
It doesn't seem to be a rotation issue, I've noticed that bug before but that's not it, it just seems that the leg doesn't wanna rotate at all. It is entirely stiff, it doesn't even bend the other direction.
Anonymous at Fri, 4 Oct 2024 16:53:13 UTC No. 997314
>>997312
Right. So, unless you want to dive into the technical reason why that happens, just pre-bend your rest pose a little bit and you'll be fine.
Anonymous at Fri, 4 Oct 2024 16:56:57 UTC No. 997315
>>997314
oh my god it actually worked!
Thank you anons! I wasn't expecting this kind of help and efficiency, but I definitely have received it.
Anonymous at Fri, 4 Oct 2024 17:02:08 UTC No. 997316
>>997315
Darn, I'm upset my leg roll idea was wrong. But still, glad you found a solution. Ask it in one of the other threads next time. There's a stupid question thread. A beginner's thread. A blender general thread. And a WIP thread. Any one of them could have handled your question.
Anonymous at Fri, 4 Oct 2024 17:03:05 UTC No. 997317
>>997316
I'm sorry, I didn't know that!
Thank you for trying to help! I have tired the leg roll thing previously, but it was already aligned properly from before :)
Anonymous at Fri, 4 Oct 2024 17:04:51 UTC No. 997318
One more thing if anons are still here: Does adding IK make it impossible to manually change the individual rig bones later? Or? Because it seems I'm unable to do so.
Anonymous at Fri, 4 Oct 2024 17:21:21 UTC No. 997319
>>997318
That's beyond my level. But I think "IK/FK switches" are the thing you're looking for. FK being the term for normal bone movement. Or "forward kinematics". Apparently, you can rig in such a way that enables you to switch between IK and FK. I never bothered to learn, because it seems too complicated. But the tutorials are everywhere you look.
Anonymous at Fri, 4 Oct 2024 17:55:08 UTC No. 997321
>>997319
Ah, thank you a lot anon! I learned a lot today.
Anonymous at Fri, 4 Oct 2024 23:37:32 UTC No. 997349
>>997319
you make a shitload of duplicate bones and throw a shitload of constraints on them
>switch bones
>fk bones
>ik bones
>original deformation bones have copy transform constraint that tracks the switch bones
>the switch bones have two copy transform constraints that track the fk and ik bones
>driver turns these on and off based on which one you want
there's a bit more to it but that's the basic rundown.
>>997318
ik will never not be buggy. what do you mean by this
Anonymous at Sat, 5 Oct 2024 01:13:22 UTC No. 997360
>>997349
At the moment there are 3 different IK solvers in Blender: Auto IK, Standard and iTaSC. They're all Jacobian-based. They also are, and to my knowledge, always have been published in a vandalized state.
I could write a book about this, but long story short, some genius 15 years ago decided that it was a good idea to put an arbitrary .85 factor to every solver iteration, which is retarded.
That's one of a dozen other major bugs that are in the C-side of things. You can't do anything about it with Python, Geology Nodes or what have you.
At least once, try IK from some other software that's not Blender and you'll see that, if implemented correctly, it's a rather nice thing.
Anonymous at Wed, 16 Oct 2024 08:19:37 UTC No. 998531
That's a tricky one. Have you tried resetting the bone roll angles? Sometimes that can help with symmetry issues in rigging.