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DogBreath
06-17-2008, 09:52 AM
Hi, I don't know much about rigging can somebody please help, I'm trying to setup the robot leg shown in the following image so that when I move the Center of Mass Control for the Torso/Hips down the legs will bend and the feet will stay planted. Using 3 HI IK chains and bones I can do this, however I want to use the objects in the image as bones.

Because of the offset of the knee in X axis, I can't use the mesh objects (with bone turned on) and an HI IK chain because the knee keeps flipping off axis forcing the hip to do the same, and then the knee no longer gives the illusion of rotating in the knee bearing.

I have attached the objects that make up the leg (minus the Foot and Ankle Bearing) preserving the pivot points of the (linked Hiearchy) FK setup, so that I have 3 bone objects. The Pivots are aligned with their parent, and their are two Eulers on each bearing.

I have tried placing a null point in front of the knee to allow control of the IK swivel angle but this has not solved the problem.

Is there a way that I can set this up with IK with the knee offset, or do the limbs have to be vertical for this to work.



http://img120.imageshack.us/img120/2691/robotimage5wa9.jpg
Illusion-shadow
06-17-2008, 02:08 PM
Which 3D package are you using? First of all, for the IK to work, the start of the leg, knee and ankle have to form a flat plane. It doesn't have to be vertical, but it have to be flat. Start with that, and you can control the swivel with a helper or have it control by the ik goal.
DogBreath
06-17-2008, 07:34 PM
Jackson thanks for the reply, Im using Max, by vertical I meant in line in the Z axis (in the up and down axis and therefore a flat plane).
DogBreath
06-18-2008, 06:18 AM
Can anyone suggest if this is possible to achieve using controllers and/or expressions, surely every robot does not have to have the same leg setup, may be i'm trying to do something that is just bad engineering.
eek
06-18-2008, 04:02 PM
check out this thread:

http://forums.cgsociety.org/showthread.php?f=54&t=617908&page=1&pp=15&highlight=leg
DogBreath
06-18-2008, 07:31 PM
Hi Eek, thanks mate, I had a quick look and that was the kind of solution I needed. I'll try that when I get home tonight.
DogBreath
06-19-2008, 09:53 AM
I've checked out the other post in a bit more detail and attempted to copy it. I can see that half of the setup is guiding the IK Chain by running parallel and that is achieved by Lookat constraints and linking Dummy's or Point objects to the IK chain, but thats as far as my understanding goes.
Its difficult to follow with Cinema4D names for objects and user defined rig component names also, and its difficult to analyse the hiearchy using the images.

I'm not sure if Max's Lookat constraints have up vector and pole vector equivelants or not, but at the moment a large proportion of my attempt to reproduce this setup is only guessing, so I'm going to have to pass on this solution and try another. Thanks.

I might try putting a control on the hip and rotating the leg once the knee is bent, then rotate the foot back to its neutral position before rigging the foot controls, adjusting the ankle bearing to align with it.
eek
06-19-2008, 04:21 PM
I've checked out the other post in a bit more detail and attempted to copy it. I can see that half of the setup is guiding the IK Chain by running parallel and that is achieved by Lookat constraints and linking Dummy's or Point objects to the IK chain, but thats as far as my understanding goes.
Its difficult to follow with Cinema4D names for objects and user defined rig component names also, and its difficult to analyse the hiearchy using the images.

I'm not sure if Max's Lookat constraints have up vector and pole vector equivelants or not, but at the moment a large proportion of my attempt to reproduce this setup is only guessing, so I'm going to have to pass on this solution and try another. Thanks.

I might try putting a control on the hip and rotating the leg once the knee is bent, then rotate the foot back to its neutral position before rigging the foot controls, adjusting the ankle bearing to align with it.


Ive used this method before for you exact problem. Max's lookat does support upVectors/poleVectors.
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