Hi, I’ve got a little problem with my character’s knee bending. Here’s two pictures illustrating my problem:
↡ Picture of a manual FK bend of the upper and lower leg. ↡
↡ Picture is a result of moving the foot IK controller up. ↡
This isn’t the result I was hoping for with the IK controls. Does anyone have any ideas why this is happening and how I might make the IK behave correctly?
Hey there!
That is definitely not the intended look 
Without seeing a file though, it will be harder to debug. It could be how the leg was posed when the rig was built. It could be something odd going on with stretch bias/stretch.
If you could send me the export file for this character, I could take a look and get back to you with a much more solid answer. jeremy.ernst@epicgames.com
Cheers!
This issue has been resolved. Special thanks to Jeremy Ernst.
Jeremy’s email:
Hey Grant!
I took a look and found a few things. In the current version, because the model has her knees locked, the joints actually form a backwards bend:
This is going to cause the IK to behave badly. I adjusted joint positions so there was a forward bend a rebuilt the rig. The results were better, but because of how her knees are locked, it was still not ideal as the knee joint was now placed too far forward.
FK:
IK:
Then I took her IK foot controls and lifted them 1 unit so her knees were no longer locked.
I exported her weights in this knew pose and exported this as a new mesh. This new pose will allow you to better place her joints to not only have the bend needed for IK, but also the have the joints centered. Attached are her weights and the mesh with the knees slightly bent. I think once the joints are adjusted in this new mesh and the weights are cleaned up, it should work great. Nude bodies are also much harder because you don’t have clothes to hide the clipping. You may want to look into doing corrective shapes as well on her knee bends to really polish things up.
Hope that helps!
Jeremy Ernst
Lead Technical Animator, Epic Games, Inc.