Hello, all.
I’ve spent some time refining my Chatter-buster arm rig. I’ve incorporated Obnomauk’s suggestions to make it easy to scale. I managed to refine my test model, so it does not have that glitchy behavior it suffered from in the previous version. Anyway, I’ve attached a zipped project file with the new version, below.
Since the Chatter-buster rig is somewhat unorthodox, I thought I’d whip up a mini-tute for it, showing how to use it, and post the information right here. If you are interested, read on.
Let’s make a brief animation where the arm flings out, as if the character was introducing somebody. Open the attached project file and create a new Action with the test model (squash and stretch demo arm.mdl). On the first frame follow these instructions to pose the arm: http://www.sonic.net/raillard/hash/Pass1a.jpg Then advance ten frames and pose the arm like so: http://www.sonic.net/raillard/hash/Pass1b.jpg What you will get will be something like this: http://www.sonic.net/raillard/hash/Pass1.mov
Not too bad for a first pass … but it doesn’t have much life or sap to it. Let’s add another key on frame 6. Pose the arm like so: http://www.sonic.net/raillard/hash/Pass2.jpg What you will get is this: http://www.sonic.net/raillard/hash/Pass2.mov
This is much better. We can make the gesture appear even more exaggerated if we lengthen the arm on the last frame. This is easy to do; all you have to do is scale the big arm control bone (2 RIGHT ARM). The details: http://www.sonic.net/raillard/hash/Pass3.jpg and the result: http://www.sonic.net/raillard/hash/Pass3.mov
Okay, this is looking pretty good. But wouldn’t it be funny if the arm vibrated a bit, at the very end, like a diving board? This is not too difficult to do. First you’ve got to create a series of four static translation keys on the wrist null (2 RIGHT HAND ik NULL). Then you have to copy and paste a corresponding set of four offset keys; you should place one between each pair of static keys. Here’s the big picture: http://www.sonic.net/raillard/hash/Pass4a.jpg Got that? Good.
In the Chatter-buster rig, the Z-translation of the wrist null is what makes the arm bend at the elbow. However, for this particular effect, we really don’t want the arm to bend at the elbow at all; it’d be funnier if the arm was as stiff as a board. So what we’re gonna do is flatten out the Z-Translation driver of the wrist null. The easiest way to do this is to fiddle with the f-curves. It’s important to reduce the magnitude of the key at frame 10, and here’s how you do it: http://www.sonic.net/raillard/hash/Pass4b.jpg Now the Z driver is ready to be flattened. You should also go ahead and sculpt the other two drivers, the X & Y drivers, into a pair of dying waves. Here’s what the function curves should look like: http://www.sonic.net/raillard/hash/Pass4c.jpg And here’s what the animation looks like: http://www.sonic.net/raillard/hash/Pass4.mov
Pretty neat, eh? Of course the torso really ought to move as well: http://www.sonic.net/raillard/hash/Pass4c.jpg And so here is the final pass: http://www.sonic.net/raillard/hash/Pass5.mov
Every arm IK rig requires some sort of mechanism to position the elbow. In the Chatter-buster rig, the elbow-pointer has another purpose; it’s primary task is to swing the IK target around, which creates nice arcs. Once you get the hang of it, it’s pretty easy to work with. It’s bloody complex to rig :twisted: but it’s easy to use.
Well, I think I’ll describe the other poses, in the sample model, in another post, if there’s interest.
Sincerely,
Carl Raillard
PS: I am fully aware that my test model has the world’s crudest shoulder. You don’t like it? Stick a COG in it. http://www.vrcops.com/CDTutorial.html 