Problem with IKAs


(Fabien3D) #1

Hi everyone !

There’s something I still haven’t reached for : the IK. I modelled a characer of mine, created an armature, and adapted the character animation tutorial to one of his arm, once creating the two new bones, and then without these two bones, but, the result is apparently not what I expected. The arm is completely twisted, and cannot be replaced the original way. I’m sure this is because of my lack of use of the Blender bones. :o

CREAFab, la création numérique autrement…
http://creafab.free.fr


(overextrude) #2

First, when you put the model in rest position, does the arm return to its normal position? Second, what happens when you clear the rotation from the bones that affect this part of the mesh (alt-R)?


(javelin) #3

don’t feel bad ,I have the same problem. It’s like his feet will
turn upside down ( sometimes just one foot) I haven’t
figured it out yet. extremely frustrating. Let me know if you do. :frowning:


(haunt_house) #4

Those sites are nice:

http://www.blender3d.com/UsingBlender/character_animation.php
http://mmaigrot.free.fr/didac-blender/ikas/ikas-eng/ik-intro.html
http://members.chello.nl/~wvanoverbruggen/animtools.html

maybe it helps

HH


(harkyman) #5

I posted something like this in the old forums on blender.nl, so I’ll try to reconstruct it here. This is the way that I do it, and I’m kind of a procedural maniac, so I’m pretty sure that I have this optimized.

  1. I start from a reference pic (or pics) placed in the background (pic of a skeleton if available).

  2. In edit mode, create your bone structure. Match it up with your reference within edit mode (purple/magenta). Pose mode (blue) is a long way away. If it is not so in your reference picture, extend all the limbs, but bend all of your joints very slightly in the way that you want them to bend later. Name all of your bones appropriately.

2a. If you plan to use IK, remember to include two extra bones for each IK limb. One is just an extra bone on the end of the limb (IK linked) for use as the contrained object later. The other bone has the same origin as the former, but will be your IK solver object.

  1. Go into pose mode and start linking everything up. If you find that something is not fitting quite right, DO NOT DARE adjust the layout of the bones in pose mode. Not even a smidge. Return to edit mode and adjust it there. When you’re done, go back into pose mode. Sometimes as you work, you’ll see that instead of one of the animation constraints, several of the bones would be best suited with a simple parent/child relationship. If that is the case, return to edit mode and do it there.

  2. Build your mesh around this bone structure. Why so late in the game? In my opinion, it’s not even worth buliding a mesh until you have a working armature rig. How will you know where to put more or less detail in your model without seeing how the bones deform? I find it that can sometimes be impossible to retrofit an improperly modelled object with a properly working rig.

4a. I use subsurfs almost exclusively for character animation. Why? The much lower vertex count dramatically speeds up both setup and revision time when assigning vertex groups and uv mapping. Also, if you are using multiple copies/variations of the model in your anim, you can adjust the subsurf level based on how close to the camera they are. Name your vertex groups to match the bone setup from step 2.

Conclusion: Basically, if you want things to work out for you bone-wise (and who doesn’t?) remember this simple rule: Pose mode is for bulding animation constraints and for posing. You’ll do most of the heavy lifting in edit mode.

Hope this helps.


(bob_dog) #6

Well, this is all fine and dandy, but I also still can’t get the “foot” bone to work on the mesh properly :frowning: . The bones themselves work fine with the IK solver. The problem is that the mesh of the foot gets twisted. I’ve tried to twist the foot bone around without any luck.

Also, when the mesh or the armature are in edit mode, the mesh “untwists” back to normal.

Surely there must be someone out there who can make this work…

Warren


(theeth) #7

be sure to apply the rotation and size of the armature (Ctrl-A).
It should clear the twistings in the deformation.

Martin


(harkyman) #8

In addition to Theeth’s note, make sure that your foot bones are unposed in their rest position. Remove any translations from the IK solver (Alt-g) and rotations/scalings that are applied to that bone in pose mode (Alt-r and Alt-s). If you need to adjust their positioning so that they match your mesh, do it in edit mode.

In fact, if your mesh changes from your base pose in pose mode to the deformation in edit mode, it probably means that your base pose is NOT at rest, but contains transformations and/or rotations.


(bob_dog) #9

Got it now :smiley: ! Thanks for the help. What I didn’t realize was that to twist a bone, you had to select both the “head” and “tail” of it in edit mode. I was trying to rotate just one end of it and not getting too far. Anyway, I rotated the foot bone around and voila! A normal looking foot, ready for animatoin!

Warren