Moho Animation Forum

So I start here:



And click to reparent the hand to the thigh (while not on frame 0), and this happens:



Any tips or tricks on how to make bone reparenting work better?

Those are target bones right? I don't think they need a parent...
I like the style of your character btw

Maybe add a bone rotation key on the thigh bone to correct which way it's rotating?

the hand on the right that's gone wrong, it has a target marker at its root, and there are two circles next to eachther, which doesn't look the same as the one on the left - is there an extra tiny bone in there somewhere? zoom in and double check if there's anything funky in there.

funksmaname wrote:Those are target bones right? I don't think they need a parent...
I like the style of your character btw

Thanks! My coworker designed the character. I'm just the rigger right now. Anyway, I put her hand on her thigh and was hoping to maybe reparent it for a few frames so I didn't have to fight with it to keep it from sliding. Not a big deal, but it just sucks when something doesn't work the way it should.

synthsin75 wrote:Maybe add a bone rotation key on the thigh bone to correct which way it's rotating?

I tried that but it seems there is more messed up here than just the IK flipping. I'm guessing that maybe reparenting a target bone might be the culprit. Or it just seems that sometimes, the longer you go with a rig, the more the local coordinates of bones get messed up. I'm starting to get into scripting (in Javascript for AE so far, but I've been meaning to compliment that with some Lua for ASP) so maybe I can start looking to make my own fix.

Anyway, thanks for the suggestions guys! I was just hoping maybe there were some common knowledge gotchas concerning reparenting. To the future!

I'd have to see the file to know exactly what the problem is. It should not require any scripting to fix.

Okay, well maybe I'll get a project file up sometime. But for now I think I've sorta figured out what is actually the problem. For some reason, when I reparent the target bone to the thigh, the thigh IK stops working, but the calf IK keeps working, so I have to rotate the thigh back into place. That fixes it for now, but at some point I'll have to figure out why the thigh IK stops working for only the new parent bone.

Edit: Wait, so probably adding a second child breaks the IK because now there are two children and you can't have an IK chain with two children if there is no way to define which bone is the IK child and which isn't. Any ideas on how to still maintain IK when one of the bones gets another child?

jayfaker wrote:Okay, well maybe I'll get a project file up sometime. But for now I think I've sorta figured out what is actually the problem. For some reason, when I reparent the target bone to the thigh, the thigh IK stops working, but the calf IK keeps working, so I have to rotate the thigh back into place. That fixes it for now, but at some point I'll have to figure out why the thigh IK stops working for only the new parent bone.

Edit: Wait, so probably adding a second child breaks the IK because now there are two children and you can't have an IK chain with two children if there is no way to define which bone is the IK child and which isn't. Any ideas on how to still maintain IK when one of the bones gets another child?

You're exactly right. Branched bone chains disable IK.

I would fix it by adding a second thigh bone, rotation constrained to the first and parented to the original's parent. Then I'd reparent the hand target to this bone instead of the thigh bone.

synthsin75 wrote: You're exactly right. Branched bone chains disable IK.

I would fix it by adding a second thigh bone, rotation constrained to the first and parented to the original's parent. Then I'd reparent the hand target to this bone instead of the thigh bone.

Oh yeah, good idea. Thanks!