2
$\begingroup$

I'm am trying to create a mechanical rig that has a foot at the end that constantly orients to the ground. Because I want to mimix an articulated robotic arm each section needs to behave mechanially - only rotating around 1 or 2 axis.

I've managed to hack together a rig that uses 2 IK chains - one for the foot portion and another for the arm. I moved the IK controller for the foot below the ground and parented it to the CTRL of the leg portion as a hacky way to keep the foot horizontal. It sort of works but there's an abrupt change in direction of the foot hinge (see gif)

I've tried locking the IK axis and using constraints to limit rotation but struggling to solve the issue that doesn't break the mechanical movement of the rig. Any experts that can help?

enter image description here

enter image description here

$\endgroup$
2
  • 1
    $\begingroup$ Can you provide a file? That'd make it easier to help you out. $\endgroup$
    – Nathan
    Commented Jan 16 at 18:55
  • $\begingroup$ Sure thing. I've updated the post with a blend file $\endgroup$
    – Callmepro
    Commented Jan 16 at 21:04

1 Answer 1

1
$\begingroup$

Before anything else: one of your bones has the wrong axes locked. Bone.008 is unlocked in Y only; it should be unlocked in X only.

Now, the reason why your Y rotation freaks out is because the IK target is enormously distant from the IK constrained bone (and, because there are multiple solutions to the IK chain.) Your workaround isn't unreasonable, but your IK target should be able to reach your IK target in most situations.

You could fix that by flooring your IK target. But instead of doing that, I'm going to recommend something instead of your workaround-- use position + rotation IK:

enter image description here

Ik target is on the floor, even like this. Its rest pose is in the same axes as the IK constrained bone. And I've now enabled Rotation on the IK constraint, so the IK chain tries to solve the IK in a way that (first) makes the final bone match the rotation of the IK target and (second, if it can) makes the final bone's tail reach the IK target.

Note: your IK will still freak out if it rotates through 180 degrees. The ultimate solution to that is to make an IK system that has one and only one solution to the problem, and your IK has a lot of solutions. But the better solution is to make your model and rig such that you don't have to rotate through 180 degrees-- know what you need it to do beforehand, and build it in the middle of likely deformations.

$\endgroup$
1
  • $\begingroup$ Thanks so much. Such a thorough and helpful answer. Much appreciated. $\endgroup$
    – Callmepro
    Commented Jan 17 at 23:39

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .