IK solver on knee problem

Burrill

Hopefully someone can help me out here, I can't figure this out.

I have a leg setup in Maya (hip, knee, and ankle joint) that has an IK solver on it. I'm trying to get the knee to only bend on it's z-axis.

Now, if my leg joints were straight, this would be no problem. However my joints are slightly offset which causes the leg to bend awkwardly.

I made a picture to better explain what my problem is, seeing as it's very hard to explain with just text.


Any help would be great!

Kurt Russell Fan Club

The IK solver will try to place the knee based on a plane created by the three points (your hip, knee and ankle).

If you want the knee to only go forwards in Y, you need to make sure the plane is flat in Y when you create the IK. The easiest way to do this is to make the leg completely flat in Y when you apply the IK.

If you want the most control, you should just add a knee look-at constraint (I haven't done this in Maya in a long time, but it should be pretty easy).

Burrill

Dang it, I was hoping there was just a box I could just check-mark and everything would be fixed.

I did somewhat fix it though. I added a another joint near the ankle and straightened the leg joints. It gives me wonky movements in the foot, but I'm really just posing the model.

keres

I believe the convention with IK joints in maya is to add pole constraints so the in-between joints orient properly.

One question though, why only on the Z axis? I think that would look rather strange.