Relative movement in "copy location" issue

Dear All,
I have a very simple scene, made out of 4 elements (see attached .blend):

  • A plate
  • Two bars (both parented to the plate)
  • An Empty (parented to the first bar, at its tip)
    My target is to rotate the first bar on its Y axis, and have the second bar rotating as well, in the opposite direction, and move so that its projection is aligned with the projection of the first one.

…I achieved this, using two constraints:

  • Copy rotation, inverted, on the Y axis, World Space - World Space (bar to bar)
  • Copy location, X axis, World Space - Local Space (bar to the Empty)

As you can see, it works fine (just rotate the Arm1 object on his Y axis).

The problem occurs when I rotate the base plate. When I rotate the Arm1, everything mess up!
I tried all combinations of Local/World Spaces, Offset and so.

What should I do?

Thank you a lot in advance!

Attachments

testingScissors.blend (474 KB)

Well, I broke my head on this problem for a long time, and in the end I came with a solution (someone may call it a “workaround”, but I don’t find any other way).

Problem that I had, presented in a more elegant way:
I want to move the center of an object (called A) according to the relative position of another one (called B) which is not “brother” of A but “nephew” (son of a brother of A), with respect to the father of A (grandfather of B).

…I could not use the “local” space of B as target of the CopyLocation constraint, since this would be evaluated as relative position of B with respect to his father (I wanted the relative position of B with respect to his grandfather, or father of A).

Solution:
I used an Empty, brother of A, which followed B by CopyLocation on XYZ (world space -> world space).
Then, I used another CopyLocation on A that followed for X only this Empty (local space -> local space).

Such solution is attached as .blend file. If someone can do better (as I hope), maybe he could tell me more… I wish I could use the CopyLocation on a Vertex(group) of the target object, but I couldn’t find it.

I hope this may help someone… maybe.

Attachments

testingScissorsSolved.blend (497 KB)