IK Trouble

Hi everyone,

I have following a few tutorials about IK rigs on youtube and vimeo. Most of them are rather advanced though and all I’m trying to do is make a very basic IK leg rig - but I’m getting very weird results I can’t make any sense of.

I have attached a video showing the results I get : basically I grab the foot handle and move the leg up, which works very well int he first few seconds, but then the leg stops following my mouse cursor and then it starts rotating like crazy and just doesn’t follow my mouse anymore.

I have also attached the blend file I have. I would appreciate a lot if someone could take a look and tell me what I’m doing wrong

Here is a screenshot of the rig :

Works very well when I start moving it very slowly :

But then if I move it a little more, even if trying to put the leg back in rest position :


ik_weird_movie.zip (375 KB)test_leg_rig.blend (424 KB)

Hey Auria,
you’ll get that strange behaviour when your leg Handle/IK-target isn’t parented to anything.
Try adding a bone, which would act as the root bone as if your rig was for a full character. Moving the root bone, would move the whole character around.

Adding root bone in bone edit mode:
Add a bone with SHIFT+a. And move the whole bone slightly below your foot Handle.
Then parent your Handle to the Root bone, by selecting the Handle first, then the root bone, hit CTRL+P and select “Keep offset”. That should fix the problem.

That rig you got, is looking pretty strange to me, with 2 IK chains for one leg? You should be able to handle it with single IK chain, to keep things simple. There is pretty good rigging tutorial over blendercookie, which covers rigging legs as well.

If you want to give it a try, see it here: http://cgcookie.com/blender/2010/01/04/rigging-an-alien/
NOTE: Watch the leg rigging part through first, before attempting it yourself.
There are some errors in the leg rig part of it, which makes it a bit confusing first.

Hi jamov,

thanks a lot for the root bone tip! Now all works great. I really don’t understand why I need this dummy root bone, but at least things work now :slight_smile: :slight_smile:

As to the weirdness of having two IK chains… that’s what I understood from watching http://www.youtube.com/watch?v=RX8H1Z87sRk&feature=related but maybe the guy in this video has some purpose for making those many chains that I didn’t get