Rigging Factory Robot Arm with Exposed Transforms Issue

[jsbenson001]

I've been following this TUTORIAL on rigging (jump to 15:40).  I have a very simple setup and I'm fairly certain I have everything linked up correctly, but I'm having a problem with the base rotating along with the IK when the IK moves.  What happens is, the rig tips over sideways and rotates sporadically as soon as the IK moves. 

My Simple Rig:

Controllers/Points: 

Outer red point - LookAt constrained to last bone in chain

Blue point - LookAt root for the red LookAt above, and the exposed xform helper

Purple point - Exposed xform helper (exposes red LookAt xforms)

Green point in the center - Black rotating base controller - Wired from z-rotation to exposed xform helper's local z-rotation

This is what immediately happens when I move the IK:

 

Just for the hell of it, I tried setting "Keep initial offset" to the outer-most red LookAt controller, which did keep the arm upright, but continued having problems:

I imagine this is a fairly common issue, but I haven't been able to find any solutions.  Can anyone help?

I've uploaded the model if anyone needs it.

[jsbenson001]

Figured it out

[jsbenson001]

So, I really didn't figure out how to correctly fix the issue. I just found a workaround.

When connecting the wire from the base rotator point to the exposed helper, the base rotator would spin about 90 degrees, but the IK goal would stay where it was. This left a pretty big gap between the goal and the bone.

The way I got around this was to offset the wire to get the rig back to the goal. For example:

Local_Euler_Z-4.687

I had to keep plugging in values until I got it right. After that, the rig works as expected.

Can anyone explain what the issue is and how to properly resolve it?

[leeminardi]

You could try placing a point helper directly above the pivot of bone001 but with a z value that places it above the arm, e.g., 200.  Then use the point to define the IK Solver Plane.  This would keep the arms from "tipping" but if the IK chain is collinear with the bone001 and the point helper (that is, directly above the bone001 pivot) the IK solver plane becomes undefined and the arm may spin.

~Lee

[jsbenson001]

Funny you should say that.  I'm setting up points for everything as we speak 🙂

I appreciate your help