View Full Version : Spline IK Legs

11 November 2002, 10:11 AM
Anyone ever set up a Spline IK leg? I'm in the middle of this rig, and I'm doing FK IK SPLINE. haha. The only thing is the feet won't really stay on the ground solid. The slide ever so slightly. I haven't had too much time for R&D on this, so I ask. 'm thinking I might need some extra pont constraints, but I don't know where. The way I have it now is spline down to the ankle and single chain to the toes. (2) parented under the foot control. It slides when I move the bottom cluster. The thing is, I've never done this or tried, so I might be looking at normal behavior. The problem with that is normal isnt selling.

Any takers?

11 November 2002, 10:54 AM
If I'm understanding you correctly, then probably what you want to do is seperate the feet from the rest of the rig. So that the feet are directly attached to your control foot/handle. That way they won't be able to move at all (except when you move the foot control), and when you move the hips or knees all that will happen is that the leg will stretch to compensate.

Secondly, how exactly are you controlling the IK spline for the leg. I'm assuming you're looking for a rubber hosing and stretch effect. If you're not doing so now, you should look into using the same solution for the leg as Jason Schlaifer uses for the spine on his DVD. Basically he uses arcLength (curveInfo node) to measure the length of the curve, and translates the joints in the IK spline so that they stretch when the curve gets longer (i.e. the total length of the joints = the length of the curve).

If you're not looking for a rubber hosing effect, just a stretch one, you're probably better of using a normal IK rpSolver.

Of course, this entire reply is assuming you're using Maya. :)


11 November 2002, 08:36 PM

I have the jsScalebyjammer. The way I have it right now, the pline IK handle ends a joint before the ankle. On the anlke itself I have 2 SCsolvers to deal with foot rotations. Those are grouped under the foot control, which is outside of all the body controls excpt "WORLD" - Using Jason's script, It reduced the amount of movement, but It's still not perfect. The foot is only sliding when I'm using the spline skeleton. Everything else is cool. I need it to be bendy bender sometimes, and sometimes not. Thedirector is looking for arcs sometimes, and angles another. I'm at my day job right now, so I can't send the file, but maybe tonight I can pass it off for you to see.

Maybe If I put both end clusters in the foot heirarchy it'll lock. I think That might have to be the move.


11 November 2002, 02:39 AM
Yeah, unfortunately this technique can never be exact, because you can't get the joints to ever exactly scale based on the arcLength.. it just doesn't work.

Instead, you can use a wire deformer, that might work..

or have the root of the leg joints start at the feet and allow it to stretch a little into the body?

11 November 2002, 06:27 PM

That's good to know. I was about to lose more sleep than I can afford. I'll test the wire out as soon as I'm done with all the pumpkin pie and ham.. mmmm... Rigging. :drool: yeah... Thanks alot man..

11 November 2002, 06:40 PM
One thing you gotta be sure about the wire deformer is that you have twist attributes set correctly.. otherwise, the thing won't rotate the way you want, it'll just bend around.

so somehow, yer gonna need to rig the twists to follow the main controls.. :)

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