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View Full Version : Problem with Wrist Twist IK in Mobu

Athey
11-29-2010, 10:46 PM
I have attached an image that details the problem that I'm having.

Basically, I have very little experience with motion builder and I'm trying to set up a model/skeleton for an animator that wants to use motion builder.

The skeleton was made in Maya and I used FBIK joint labels so that the skeleton would have IK when brought into mobu. I was following instructions from someone who knows mobu pretty well, but I no longer have access to this guy to help me troubleshoot the problems I'm encountering.

When you select the wrist ik handle, I need to be able to rotate along X (twist the wrist) and have the wrist twist bone rotate partially, but not rotate the elbow bone any at all. For some reason, when you rotate the wrist, it's also rotating the elbow joint.

I have no idea why it's doing this, or how to make it stop.

Any clues?

Any help is GREATLY appreciated. I'm kind of on a deadline, so if anyone could help me out, I'd be eternally thankful. ^_^;;


TIA
Athey
11-29-2010, 11:31 PM
Okay, I have a new theory, but have hit another brick wall with it.

From what I can tell, it's actually rotating by the global axis and not rotating around the local axis of the wrist bone.

Like I said, i have limited experience with Motion Builder and I cannot figure out how to switch to local rotate mode.

Any help?

TIA
Athey
11-30-2010, 12:47 AM
Okay, being local vs global didn't change it. It doesn't seem to be a problem on motion builder's end, specifically, since I've realized that it does it in Maya when I select the FBIK controller for the wrist. So I think it's got to be in there somewhere.

I set the wrist twist bone to none, but that didn't make any difference.

The elbow needs to be elbow, so I don't think that changing that bone would fix it. Does anyone have any suggestions at all? I'm reaching the end of my ideas and hitting a brick wall is giving me a headache.
ErikSvensson
11-30-2010, 07:44 PM
I have to tell you that roll joints never really worked (at least not for me). What I usually do is to just clean them up manually later on by removing all the keys and bake the roll joint again. :) Usually fixes most of the problems.
Athey
11-30-2010, 08:38 PM
Unfortunately, it's not the roll join that's causing the problem. I don't care if it moves at all. Right now, the problem is that the actual elbow joint - the whole forearm bone - is rotating with the wrist.
ErikSvensson
12-01-2010, 01:17 PM
Oh sorry, my bad! I just tried myself and for some reason that join keeps rotating... I can't remember us having this kind of problem at work but that was MB7.5 ext. 2, and I tried in 2010 now.

Ok I found a solution, go to characters -> your character -> control rig

Under modifiers -> roll extraction -> put the Forearm Roll to 100%, put the roll solver to 7.5 and finally the roll extraction mode to absolute. Let me know if it works! :)
Athey
12-01-2010, 05:12 PM
I definitely really appreciate you trying to help, so thanks a lot.

Unfortunately, my menus don't seem to be laid out the same, and I don't see anything about control rigs.

I attached an image of what I see when I go to the Character menu. Don't know if that'll make any difference.
ErikSvensson
12-01-2010, 06:26 PM
Ah I meant in motion builder, not in Maya. :)

http://img208.imageshack.us/img208/7387/forearm.th.jpg (http://img208.imageshack.us/i/forearm.jpg/)

Uploaded with ImageShack.us (http://imageshack.us)
Athey
12-01-2010, 06:46 PM
YES! Thank you thank you thank you. I've been struggling with this for a week and it works. Thank you soooooo much.
ErikSvensson
12-01-2010, 07:14 PM
Awesome! And if you get more issues don't hesitate to contact me directly. Got my contact info on the blog. But I'm lurking in this forum as well so posting here works too! :beer:
bclark
12-20-2010, 01:23 AM
I cover the roll issues in my mobu dvd and on the blog.

The roll system will always twist the elbow in its current solving mode, you don't have to be in absolute or in 7.5 or anything you just have to set the extract to 100% to force the roll joint to work.

Because of the elbow issue, many people simply create a roll rig from scratch or use the "built in roll" to drive a real roll rig.
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