Rigging Questions

Hey there, just a couple rigging/constraints questions.

  1. When I make an IK chain for say, the leg of a character, The deformation works fine as long as the target of the IK constraint remains behind the hip in Y-space, but when it moves infront of the hip in Y-space, it deforms the mesh as if it had a reverse-joint knee. I realise this is because rotating the bones in sich a fasion is the most direct way to reach the target IK bone, but I know there is a way to control this. Any help would be great.
    (Yea… I’m not finished with the weight painting)
  2. When I add “Track to” constraints to eye bones to track a gaze bone, how do I prevent a cross-eyed effect when the gaze bone is close to the head? At the moment I am just placing the gaze bone really far away from the mesh, but it’s rather inconvenient. Once again, any help would make my life alot easier.

One technique that solves the knee problem is to add a target bone in front of the knee, and a track to (? not sure) contraint to force the shin to point in that direction.

For the eyes, add a master eye target, with separate left and right eye targets parented to it. The left and right targets are far enough apart so the eyes don’t cross. If you need the eyes crossed at some point, you manipulate the left and right eye targets directly.

As an alternate, you can rotate the eyes out slightly to make them “wall eyed” when unconstrained, then point them at the single close-in eye target. This is nowhere near as flexible as using separate targets.

Thanks alot for the help, it worked perfectly. Here are a couple other problems I’ve got that you could probably solve.

  1. When I have an IK chain, I don’t know how to allow FK. When I try to rotate the bones they remain rigid because of the IK bone.
  2. When I generate particles for hair, and have a null object with a force field to shape the hair: how do I parent the null object to follow a bone in pose mode so that the hair doesent change through the animation if the character moves?

A little off-track, but I have to say I am amazed at how incredibly helpful this forum is already, I’ve been using blender for about 3 years now, and been teaching myself from scratch VIA random video tutorials, so it’s been a very slow process. It’s helping to fix little problems like these that tutorials don’t cover, and so having a human being to communicate with who knows what they are doing is an amazing new resource for me. So thank you all very much for your help!

  1. You can key the influence of any constraint, IK solver included . There are some issues apparently with switching between zero (no influence therefore FK) and 1.0 (full IK) for some people … though if you key the driver object properly in the animation I have found it works well enough …

But here is how you set up a IK influence slider :
A) Split up an area and turn that into a IPO curve editor window (if you didn’t have one open yet) and switch the ipo constraint type to “Constraint” (hit the up/down arrow next to the “drowning man” icon and the ipo types available will show)

B) Now go to the IK solver panel you want to key the influence of and hit “Key” . The only available curve for constraints (Inf) will show up blue as a horizontal line .

C) Now go to the IPO curve editor window and while holding down the Ctrl key click with the LMB to add a new point on the curve somewhere close to zero along the Y axis .

D) Now hit N while in the ipo editor . The Transform Properties window will pop up and from there hit “Add Driver” . An “OB:” field will show up . Add a cube which will act as the driver into your scene . Now type the name of the cube into the “OB:” field . and a couple of dropdown fields will show up … there are various options for these but for now leave them as is . The Object field indicates that you are using an object type to drive the channel and Loc X indicates that the location of the driver object along the X axis determines the travel along the curve .

E) The final part of the set up just requires some editing of the Inf curve . Change the Interpolation Mode to Constant for the curve . Then tab into point edit mode and select the point closer to zero along the Y axis and manually input “Vertex X 2.00| Vertex Y 0.00” into the respective fields . This means that when you move the cube driver object 2 BUs along the X axis the IK constraint will have no influence and so effectively it is now a FK bone .

That’s it . Now when you move the cube 2 BUs along the X you will have FK … move it back and you will have IK back …
And finally here is a rig that already has that installed and made to look pretty : http://blenderartists.org/forum/showthread.php?t=106275

  1. Just parent it . Select the null (empty?) and then shift-select the head bone or whatever and Ctrl-P in Pose Mode . Now the null will move with the head bone .

Wow three years alone in the wilderness of Blender … Well welcome to Blender Artists ! I have been using Blender for about a year myself (started when I joined here) and having this forum has helped accelerate my learning Blender quite a bit . Trying to help out with questions/problems that users have is a great way of learning the program .

Thanks alot for your help. It’s been a rough road since the blank stare I gave the UI when I first opened the program, and I’ve learned very slowly. Though I can tell how much help this forum is going to be, 2 posts and I’ve had problems solved that would have probably taken me months (granted the time I have to actually use blender). So thanks again.

Hah! :smiley: I know exactly what you’re talking about. I’ve seen it, in the mirror. Welcome to BlenderArtists.