Armature leg goes wonky when I pose

(Soulstorm) #1

When I set up an armature it flips over at certain angles (more or less at 45 and 275 degrees. whats up?

I create a standard 3 bone armature, add 2 empties to the foot and set up an IK solver, nothing fancy. Now, when I move the heel everything works fine up untill those angles I mentioned.

here is the blend file:


(WeirdHat) #2

If the leg (or whatever it is) is bent when you make the IK constraint, it shouldn’t do that.

(Paul_C) #3

Yes, I had this problem all the time. The reason is (I think - correct me if I am wrong - I lurve being punished) when you bend an armature on the opposite side of the parent bone, it doesn’t know which way to bend, so mathematically, it thinks bending backwards is just as correct as bending forwards. What I discovered is in a foot IK setup, go into pose mode and rotate the “thigh” bone forward about 60 degrees. Because of your IK restraints, the bone won’t actually move, but you’ll notice the degree counter displaying the number of degrees at the bottom of the main screen (on the bar that sparates your viewing area with your button area) Now when you move your foot setup, your “knee” won’t buckle back. Try it and see.

Hope this helps (was I clear?)


(Soulstorm) #4

…go into pose mode and rotate the “thigh” bone…

I actually noticed this the first time I set the armature up. Pre-blender 2.20 when IKAs were the norm, this didn’t happen - is it a bug in the IK solver?

It isn’t realy a problem with the leg because it wouldn’t normaly bend that far, but arms would be nice if they didn’t flip all over the place when they reach above the head!

oh well - maybe i’ll just wait till I can get Publisher. I heard something about baking keyframes - then I’ll just use forward kinematics when things get funky…

(Hos) #5

IK can act be somewhat unpredictable at times.
That’s why I use elbow and knee pointers – not only
so they help allieviate flipping problems, but they
also give additional control to do poses that would
be almost impossible otherwise (and you can make
you character do the funky chicken very easily).

For examples of rigs with knee and elbow pointers
check out the first three blend’s on my page:


P.S. Don’t use empties for solvers (negates the
benefits you get from using the action window).
Please see the thread “How to Get Ahead in
Character Animation” at the top of this forum for
some rigging tutorials.