Help with Rig

Hello I’ve had this trouble for the longest of time and I just can’t find how to fix it.

I have attached a blend file. The .blend file I’ve included has IK on the arms and legs. To see the problem I’m dealing with go into side view, select either of the two null objects that are near his feet and then move the null object backward. The IK works beautifully, the knee bends as expected to get the ankle at the target null object. Now move the null object forward so it’s in front of the character… the knee joint snaps to being straight and the IK seems to make no attempt at putting the ankle at the target null object. Move the target object behind again, works perfectly. Move null object in front again, knee joint straightens and refuses to bend.

Can anyone help? What have I done wrong here?

Made with 2.49

I’m not an artist, I’m a programmer (hence why the model looks so bad) and this is my first attempt at a rig, but I really like the art side of making games as well… and I really want to animate my own character and get him running around T___T I would be soooo thankful for any help!

Attachments

JustinRigStanceWithIK.blend (237 KB)

In the rest pose, the knee joint is absolutely vertical, perhaps even a little ‘concave’. The IK solver has no hint that it should try to bend the knee forward. When you move the IK target forwards, the IK solver naturally tries to bend the knee ‘the wrong way’, and then the set limits on rotation kick in (oops, unfortunate metaphor there …) and straighten it out again.

The informal but effective solution is to have the knee slightly bent in the rest pose.

A more systematic solution is to add a pole target. This could be trickier than usual since you have chosen to make the IK constraint be on the head of the foot bone rather than the tail of the lower leg bone, which means that the pole target will orient the ankle as well as (or instead of) the knee.

Best wishes,
Matthew

Thank you very much! Bending the knee back slightly at rest works perfectly!

I’m finally able to start animating, this is a big relief, thank you!!!