View Full Version : Any ideas for rigging a multi-limbed leg?

03 March 2008, 09:54 PM
This problem has boggled my mind for some time now.

I want to rig a robot that has a leg with six limbs instead of the "normal" hips:knees:ankle. It of course has to be some IK-setup but I still want the animator to have individual control over each limb. To make things worse, any limb should be able rotate freely and not be constrained in the way a knee or elbow is. Please see attached pictures.

The only idea I have so far (see attachment) is to make the last three limbs work in IK and the rest in FK. At least the foot can then be planted in IK to some degree and the rest can be animated freely, but it doesn't allow for any fast posing and it's gonna take along time to animate, plus the middle joint of the ik-chain will have limited rotation. I read about the ELASTIK solver for Maya and it looked like it could solve some of my issues but it's not available for maya 8.5 or 2008.

Any ideas would be greatly appreciated.


03 March 2008, 12:22 AM
Try this. ( I went ahead and made up something real quick based on the drawing. Not actually having the leg I may not have the angles right, but the functions of the controls and their influence on the bones is really all I was worried about. Ignore the outliner :eek:, it's not cleaned up or organized, so it could be confusing. And for every control I just made it a circle, IK or FK, I love circles. Let me know if this is what you meant though, if not I can make adjustments.

I don't know if this will help also, but this ( is a multi legged rig, not a robot, that I have done.

03 March 2008, 03:43 PM
Thanks Jason for the reply.

I took a look at both your rigs but unfortunately it didn't solve much. What I want is a setup that is mostly automatic so that the leg can easily be posed with the feet sticking to the ground or whatever, but still having the option there for the animator to have precise control over every limb. I don't think that can be achived with any "standard" fk or ik solution. If one could just put have ik on the whole chain but the be able to tweak each bone individually without breaking the solve then that would be ideal.

03 March 2008, 06:38 PM
My bad, I went off of "make the last three limbs Ik and the rest FK" and the picture where you had an IK drawn. Sorry the examples weren't of any help to you. I believe I now understand what you are looking for though and will probably give it another go here in a few days. I'm laying some hard wood flooring and don't know when I can get back into Maya. It is on my mind though and I like your idea. Keep us posted on your progress, especially if you come up with a solution :D .

03 March 2008, 01:52 PM
I had a play around too, and I am not quite sure if this is what you are after.

The set up is only currently working in rotateZ, but to expand to all rotations, you just need to modify the expression.

The idea is having the fk chain following the ik chain, with an optional offset (this is the expression). The problem is though to lock the end of the fk chain and stay planted, I cant find a way of doing it yet without having the last joint stretch. I was thinking of giving the option to stretch the fk joints separately to allow the animator to correct this problem, but it would be a pain to constantly counter animate the joints so that they stretch evenly along the chain. Hopefully this is close to what you need though.

Here is the link to the file.

edit: the leg_ctrl locator is the control object you use to adjust the joints individually. This object would be your foot controller on the finished rig.

03 March 2008, 09:56 PM
Yeah I thought of doing something like this to but like you said, it would be really cumbersome to counter-animate. Once you start to edit in fk, and don't want any stretching, you lose all the benefits of IK. I think the only way to get a really solid solution would be a different IK solver that enables you to offset the rotation of a joint in the chain and then have the rest of the joints solve automatically to reach the end position.

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03 March 2008, 09:56 PM
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