0
$\begingroup$

New here.

I've been implementing some basic IK stuff for a rig of mine. The arms, the legs, etc. Overall I'm happy with how it's been going, but there is a problem.

Whenever I go to push the rig's arms into a more complicated position (in this case, a casual "hands on hips" sort of pose) I end up with some very twisty deformation at the wrists and shoulders.

enter image description here

enter image description here

There's an option to "preserve volume" for the mesh on the armature modifier, and that would be a decent enough band-aid except I need to export the model into Unreal Engine, which won't accept modifiers.

I think this might be a common issue for newbs like me, but I haven't found a clear solution online yet. Hopefully someone here has some suggestions! Any help is appreciated.

EDIT: Here's a PasteAll link to the .blend file if anyone wants to take a direct look: Blend File Link.

$\endgroup$
  • $\begingroup$ Possible duplicate of Shoulder deformations $\endgroup$ – Duarte Farrajota Ramos Dec 14 '18 at 19:08
  • $\begingroup$ You need twist bones, for both humerus and forearm. Shoulder is rotating in Y axis when it shouldn't (fixable with locks, if not using a pole.) But fixing it will leave your elbow in wrong position, for which you need a humerus twist. Same for wrist: your hand bone is at too strong local Y rotation compared to forearm, but can't change forearm without breaking the elbow's angle lock-- unless you add a forearm twist. (Weights, and likely bone placement, are not ideal either, but the twists are the major issue right now.) $\endgroup$ – Nathan Oct 15 '20 at 1:25
0
$\begingroup$

For the elbow, it looks like your arm is pivoting on itself. Think of like a rope you hold tight with one hand and you twist with your other hand. It's what's happening here.
A solution for that would be to lock the bone's rotation on its Y axis. Either through a Limit Rotation constraint, either in the bone's Inverse Kinematics panel:
demo pic

Otherwise, understand that bones do only one thing: rotating vertices around. The "preserve volume" does help to keep the volumes, but it doesn't do any miracles. When two bones rotate on each other, there's always a point when some vertices go the wrong way.

And that's why we use "Corrective Shape Keys". Just make some of those and you will be fine. Also, there are some addons out there (like that one) that might help you create your CSP faster. But start manually, so that you learn how it works and understand how everything works.

$\endgroup$
  • $\begingroup$ Took me a minute to find the right configuration, but I think it's looking good! Thank you for your help! $\endgroup$ – Cinebeast Dec 14 '18 at 17:46
1
$\begingroup$

rig modifiers Similar to L0Locks answer an alternative is to add a copy rotation modifier with 50% influence to the next bone up the chain. By setting the influence to 50% the rotation will blend with the rotated target bone providing a smoother transition. Definitely not perfect but good for a quick fix. Note: you may have to play with the axis invert setting depending on your rigs orientation.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.