View Full Version : Basic Arm Setup Question

02 February 2004, 04:05 PM
OK, I have a quick question regarding arm setup. I am using the arm setup detailed in the AW/Character Animation Certified Training book (Melvin-page 58). I have followed the steps outlined verbatim and there is one thing I keep running into.

It says in the book to create locators for each arm in order to control the IK Rotate Plane solver's pole vectors (you constrain them to the locators). Easy enough...I create my locators move them into position (slightly behind the shoulder joints), freeze transformations (so I can zero them out to return to a default position). After constraining the pole vectors to the locators, the book states that although not necessary, if you want the locators to move with the body during animation (which I do), to parent them to the collar joints.

Here is where I run into my problem. Once I parent the locators to the collar joints, they inherit the local rotation angle of the collar joint. So after they are parented they are tilted at an angle and no longer in their straight up-and-down default position that I originally placed them in. If I were to rotate them (the locators), they will rotate according to collar joints local axis, and not the world axis. I don't want to change the collar joint's axis to world space because then they won't be oriented to the rest of the joints in the arm.

There's no mention of this issue in the book, and maybe it doesn't matter, but I notice in all the pictures in the book, the locators are not tilted on an angle like mine are when I follow the steps provided. Is it normal then for the locators to be skewed like I am getting after parenting them to the collar joints and they just don't show it, or was something left out of the book?

Any thoughts.....?

Thanks in advance....

02 February 2004, 12:21 AM
Hey Rick. There's a number of things that you can do. Personally, I would recommend NOT parenting the locator under the collar bones. If the arm IK is separate, then keep the locators separate. If you haven't yet, I'd seriously think about making an IK/FK arm (take a look at Rigging 101 ( it will make life a WHOLE lot easier for ya if you plan on moving the character around a lot (which is why I assume you want to parent in the polevectors).

To prevent the locator from flipping, you might want to make sure your "Preserve postion" checkbox is checked under the EDIT-> Parent options.

Finally, there's one more thing I'd recommend giving a try. I've noticed that many people create a completely separate "control hierarchy" (spelling?), so that animators can jump up and down the hierarchy with the arrow keys and not have to worry about cycling through parts of the rig or geometry that don't need to be fiddled with. In other words, if the locator is going to be the actual control that the animator is going to use, I wouldn't parent it under the bone itself. "So then what do you do?" you ask? Well...

To better illustrate what I mean: Simply group the locator to itself and center it's pivot. Both the locator and the group node above it should now have their local rotation axis aligned with one another. Now, create another group ('transform node" or whatever you wanna call it) by duplicating your locator's group node and deleting the duplicated child locator that will also be copied. Now move this new/duplicated transform/group node under the collar bone. Now just orient and point constrain the locator group node to the group node that is under the collarbone.

Make sense? If not, give me a page and I'll try and walk ya through it.

Man.. that took longer than I expected.

- Jeremy

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