View Full Version : IK Rotate Plane Weirdness

08 August 2010, 06:37 PM
I'm setting up a leg rig, and I'm having issues with IKRP solver. when I add the IK handle, the pole vector on the rotate plane is on a vector that's pointing to the right, instead of to the front. when I add the pole vector constraint, the pole vector now faces straight ahead, but the whole leg has rotated to the left, so the offset between the rotation plane pole vector and the leg remains constant.

So, when I bent the knee or raise the ankle, the knee bends to the right instead of to the front.

I know that the vectors on the XZ plane from one joint to the next determine the direction of the pole vector, but I can figure out how to work around this.

I've include screen shots of the front, side and perspective view of the mesh (templated) and the leg rig, and the same with the knee bent. These shot are without the pole vector constraint, 'cuz when I add that, everything gets REALLY wonky.

how do I fix this, or what am I doing wrong?

08 August 2010, 07:10 PM
if your knee is bending right to left instead of front to back, this usually is a case of setting prefered angles. You can set you IK Blend on the IK chain to 0 then grab the Bone bend it and set perfered angle. Then you can set you IK Blend to 1 to Turn IK back on and the Leg will snap back into place the second you move the IK chain.

08 August 2010, 12:12 AM
not sure what you mean by "grab the Bone bend it and set the preferred angle". Grab which bone? There's 2 joints in the knee. Do you mean one or both of them? By "bend it", do you mean rotate it? Then choose "Set Preferred Angle" in the Skeleton menu?

I tried turning off the IK blend, rotating both knee joints so that the leg was bent the way I wanted, and setting the preferred angle. When I set the IK blend back to 1, everything went really wonky. The whole leg rotated, it still bent to the right, and I couldn't get it to return to the original position.

And the pole vector in the rotate plane still pointed to the right, the direction that the knee was bending.

08 August 2010, 05:51 AM
since your having trouble with that. delete the IK so that you starting fresh. Position your leg into a neutral pose so that it will line up with your mesh.

Bend (Rotate) your knee so that your joints are bending in the correct direction. Right click on the each joint and set perfered angle. Rotate the Bones back into place.

(Usually I will Build my skeleton, Bind it, then rig. This allows me to Set my prefered angles then snap back to my bind pose.

Using IKRP (Rotate Plane) set your IK. Then use IK SC (Single Chain) for the Ankle to the Ball and then again for the Ball to the Foot.

older post with Leg sample

08 August 2010, 06:04 AM
make sure , all 4 joints are "planar" . do this , you can create a simple nurbsPlane and use a geometryConstraint on each of your joints - then each joint will be planar to each other .

2.delete the plane
3.orient your joints

08 August 2010, 07:29 AM
If your creating them from the side view they will automatically be planar. No need to do anything special.

CGTalk Moderation
08 August 2010, 07:29 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.