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I am modelling a Monitor Stand for triple monitors. I would like to rotate the right arm and have that rotation reflected in the left arm.

Starting point with the arms straight and the right arm (the draggable one) selected.

Starting point with the arms straight and the right arm (the draggable one) selected

I am using the Copy Rotation constraint on the left arm. The settings suggest that left arm should rotate when the right arm is rotated.

The settings suggest that left arm should rotate when the right arm is rotated

The rotation works as expected but obviously in the wrong direction for my purposes. Rotate the right arm towards me and the left arm rotates away.

Rotate the right arm towards me and the left arm rotates away

So I change the left arm constraint to invert the X rotation, expecting the left arm to come towards me when the right arm is rotated, but instead I see no rotation whatsoever.

Inverting the X rotation produced no rotation at all

In the initial state both arms have zero rotation (all prior rotations have been applied)

Where should I look within my model for the issue?

Thanks.

BTW. I notice that in the viewport when location axis are locked then the corresponding 'drag arrows' are not drawn but when the rotation axis are locked then they are still drawn in the viewport. Is this an indicator of where the problem may lie?

Blender 4.1. The Align tool in 4.2 is broken :(

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  • $\begingroup$ Please consider checking the question's preview before posting it to make sure you did not mess up all the image links. $\endgroup$ Commented Aug 14 at 17:03
  • $\begingroup$ Since you are rotating and copying the Z axis, why do you invert the X axis rotation? Apart from that you do not show this setting, so hard to tell if the constraint is set up correctly when you don't show the final settings (hint: if you set the constraint to invert X instead of Z this is not going to work as expected). $\endgroup$ Commented Aug 14 at 21:27

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I do not know if "invert the X rotation" was a typo and you actually wanted to say "invert the Z rotation" because have not reacted yet and not posted your constraint settings. If you have inverted the Z rotation and it does not work, it might be necessary to inspect your file where the problem lies.

Even if you mistakenly inverted the X rotation, it is strange that the left arm does not show any rotation if you did not change anything else - because inverting X should still rotate the arm incorrectly on Z.

However, maybe you have changed the Target space from World Space to Local Space? In this case the left arm will not rotate - because the right arm is not parented to anything, which means whatever rotation you give it, is 0° on its local coordinate system, since it rotates with the arm. Use Local Space (on Target as well as Owner) only if the object you set to local has a parent coordinate system / frame of reference in relation to which you want to copy the rotation.

Anyway, if you set up your constraint like in the following example it should work:

copy rotation constraint

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