IKH Gets Displaced when I move the Arm. Any tips?


Hello everyone. I just created this account to start with this question because I’m trying to solve this IK problem for days now and I don’t know where else to ask.

This is a complicated set up so I hope that I can help you understand what is going on.

I’m almost done rigging the arm of this APU machine from the Matrix.

It starts with two FK controls in the shoulder (one CTL for each Axis), then goes down to another control for the elbow, then a Twist control for the rotation of the lower arm and then the IK control.

The IKH is parented to the L_armTwist_CTL and both the IKH and the Twist control are point contrained by the gunIK_CTL. That way I can automate the rotation of the lower arm and the translation of the IKH with just the gun control.

The rig gets messed up when I rotate any of the two controls above the Twist_CTL (that is the L_elbowFK_CTL and the L_armRotateForward).

Both the IKH and the gun control lose their original positions and I have to reload the scene before trying something else. “Undo” doesn’t fix it.

Any idea what I can try? Feel free to ask any questions.


Here some more screenshots to help you understand.



Did you try deleting the ‘pointConstraint’ and just parent the IKhandle to the controller?


Yes. Same thing happens. Exactly as in the 2nd screenshot. Im starting to think that the IKH itself has errors, maybe even in combination with the pole vector. Maybe I should recreate it from scracth?


I would delete it and create it again… I hope it fixes it!
If it’s still happening and you feel confortable sharing the file, I could take a look.


So I tried it again multiple times. I even tried a single chain solver IK.
Same thing happens. Once I move the IKH it gets displaced. I have no idea anymore.
If you’d like to check it out here is the file for download.



I’ve been working on it again today and found out what the real problem is. It’s the aim locators for the twist control. :open_mouth:
I parented them to the Shoulder Rotate Control and now it is almost fixed. I can move the gun control and rotate the shoulder control. Only when I rotate the L_armRotateForward_CTL the entire lower arm spins because the aim locators are following the control above it.


SOLVED! I parented the aim locators to the elbow FK control. It was that simple -_-


Sorry for the delay!!
I am glad you found the problem! :metal:t3: