PAE: Wrangling IK Arms

No, PAE is not an abbreviation for "paella" -- it stands for Personal Animation Epiphany, and I had one in the hot tub today as I soaked away my sore muscles. I saw someone resting his elbows on his knees and holding his head in his hands, and then he started to bounce his knees and (of course) the elbows responded. And that's when it hit me...

This has been giving a lot of students problems when it comes to arms, getting a good sense of connection in the arms. This shouldn't be news to anyone that has animated, but if you use IK arms (which behave as marionette would behave) as opposed to FK arms (which behave as stiff old Barbie would behave) you know that it is easy to get a detached feeling with the arms - especially if you're not a seasoned animation veteran.

I once heard it said that you shouldn't even think about using IK arms unless you had at least 4 years of experience under your belt. But be that as it may, just like teenagers with sex and alcohol, if people are going to do it anyway, best prepare them so they don't screw things up too badly.

Not that I'm an expert on the subject myself, but having a decent working knowledge of the results of IK and FK, I think I've wrapped my brain around an important concept.

If you're going to animate with IK, any time you move the spine or hips, move the IK handle respectively. You see, the aggravating/wonderful thing about IK is that it will stay put no matter where you put the spine or hips, but if you're animating something that isn't "planted" and insist on using IK anyway, you have to mimic what would happen if the arm was connected to the body. That means the arm goes where the body leads and any action on top of that needs to be layered in.

Otherwise you will get arms doing their own thing and the body doing its own thing, and it looks more than a little bit wrong. I think that's where people are misstepping - the point where the trunk of the tree moves, the limbs must follow. They must react. Leaves can do their own thing on top of the bigger action and there can be overlap in the branches, but the branches can't lock in place when the trunk is swaying. That immediately takes the viewer out and think "woah, something is wrong here. I'm not sure what, but people don't move like that..."

Please comment if you have anything to add to this discussion.