CGTalk - leg setup problem

jHromika

08-03-2003, 08:10 PM

ok, typically, for say a human biped the leg chain is built on the YZ plane right? well, for this robot character I'm rigging, the model is built so that the knee bends on the XY plane. Not a problem I thought, I can rig it the same way and just place the kneeAim control out along the x-axis instead of the z-axis.

Well, after rigging it that way, I find out the knee is supposed to bend as if it's built along the YZ plane. Naturally I can't just make a chain along the YZ plane because the joint pivots won't be in the locations they need to be in and the deforms will be horrible.

If I want to keep this rigged as IK, the only thing I've been able to come up with is to make another hip -> knee -> ankle chain built along the YZ plane, then IK that and write an expression to link the old chain with the new so that the leg deforms properly and points down the z-axis instead of the x-axis. The only problem with that, is I'm assuming I'm going to need some kind of offset for the two chains, which I haven't figured out yet.

So if anyone can come up with a solution, I'd love to hear it. Even if its just a "I think this might work, give it a shot and see" type of response.

Thanks!

cavetroll

08-03-2003, 08:44 PM

there is absolutely no reason why you shouldn't be able to build a leg in the xy-plane. just be careful to draw your joints with a slight bend in the direction you want them to rotate. if you didn't do this, your ikSolver won't know which direction to bend the joints. anyway you can help the solver a little bit by setting the preferred angle on your lowLeg_joint in case you did draw your bones in a straight line.
just turn off the evaluation of your IKs (or make them not Sticky), rotate the lowLeg some degrees in the desired direction and rightMouseButton -> "set preferred angle" on the joint.
hope that helps you out.
cheers. :)

jHromika

08-03-2003, 09:09 PM

well, I tried something similar to that before I started messing with the expression and it didn't work. But, in the event that I goofed, I tried again. I added a slight bend to the knee joint along the YZ plane, set prefered angle with kneeJNT selected, and then added my RPSolver IK. Unfortunately I ended up with the same results :(

I could be wrong here, but I get the impression that setting a new prefered angle won't work because the chain is still more XY plane oriented that YZ (if that made sense). So it kind of works, but I'm still getting the majority of the rotation around the Z world axis.

Or am I still doing something regarding the prefered angle incorrectly?

jHromika

08-03-2003, 10:44 PM

Apparently everything I thought I knew was wrong. The problem was fixed by drawing the chain on the YZ plane as if the geometry was there too. And here I thought I needed to place the knee joint inside the knee...

Whatever works I guess. Anyway, thanks for the help :)

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