topic Re: Forearm rotation in MotionBuilder Forum

Forearm rotation

Anonymous — Tue, 17 Jan 2017 13:28:08 GMT

I have a problem. This is my model:

My target is "rotate the right forearm" but I don't know how. If I rotate only the red sphere on the hand, it rotates only the hand like the image below

As you can see if I rotate the hand (red sphere control) the forearm will keep the positon and will not follow the rotation of the hand; this situation creates distorsions.

If i try to rotate the bone representing the forearm, this one doesn't move at all.

How can I fix it? Should I switch to FK control? How can be done this switch?

Thank you so much!!

Re: Forearm rotation

jps — Thu, 26 Jan 2017 13:00:13 GMT

You should be able do that by changing the roll parameters in the character properties. You should be able to define how the twist rotation spread over arm and forearm.

Depending what will be the final use of this character, you might not want to twist from the elbow.

If it's designed to be use on a game engine with lots of blended animations, you might en up with wired blend result if your elbow is rotating on more than one axis. Generally an elbow has just one free rotation axis. When you twist your wrist it's not twisting at your elbow.

That's where you use extra bones to get better body deformations. That can be roll\twist bones or any other kind of extra rigged bones.

Generally I'm trying to avoid using MB control rig roll bones. I prefer to create my own deformation rig and have a full control over it. I had bad experience using MB control rig roll bones in the past, especially with character animation sharing.

Re: Forearm rotation

Anonymous — Fri, 27 Jan 2017 11:50:05 GMT

Thank you! I understand the point . . . dealing with your method, is there a link//video or a site where I can follow this idea of "extra bones to get better body deformations"? My initial animation is created from a motion capture program. I use Motion Builder to clean and adjust the entire animation