Using custom transformation orientations in rigging

Question

So, I have a robot that I am rigging (think eve from the pixar film Walle). It's shaped like a large diamond. https://ibb.co/cSCOPb. But the four bottom panels open up so that it looks like this: https://ibb.co/bHzRcw. The way that I am currently doing it feels really janky. Since I want to rotate the panels along an axis that isn't solely x, y, or z... I've created my own custom transform orientations.

This might be a side-problem, but I can't really rotate using the transform manipulators. It works fine for scale and position, but anytime I click on them to rotate it just moves the 3D cursor instead. I can find one or two tiny and specific spots that allow me to rotate using the manipulators.

And I haven't found anything that adresses using the lock axis hotkeys for custom orientations...

Furthermore, I'm trying to translate all of this into a rig. Since the panels only ever need to go from rotation A to B or in the middle, it'd be great if I could just create a rig that limits the rotation to those values, but I'm having a hard time figuring out the rig constraints to do that...

So.... Overall question is: Can I rotate on my custom axies using axis lock hotkeys?

Follow up questions are: Is there a better way than that? And can I create a rig that essentially does it for me?

Answer 1

Rigs (and Armatures) are made for that exact purpose.

I will create a rig with the topological help of the given triangle shapes.

1. Hide all but one triangle (we'll rig this one first). ⇧ Shift LMB, H
2. Add an armature. ⇧ ShiftA > Armature

Next steps are demonstrated in the following image.

3. Snap the 3d cursor to one of the top vertices. LMB, ⇧ ShiftS > Snap to selected
4. Add a helper empty.
5. Snap the cursor to the adjacent top vertex.
6. Go into edit mode of the armature. Snap the bone to the cursor. ⇧ ShiftS

7. Go into pose mode with the armature selected. ⎈ Ctrl↹ Tab Then select the bone.
8. Go to the bone constraint tab. Add a damped track constraint.
9. Set the empty as the target.
10. Apply the Pose as Rest Pose. ⎈ CtrlA
11. Delete the helper empty.
12. Parent the mesh object to the bone, by selecting the mesh object first LMB, then ⇧ Shift LMB selecting the bone and pressing ⎈ CtrlP > To Bone.

13. Set the bones rotation order to any other but quaternions. Lock the X and Z axis.

The triangle is rotated only by rotating the bone.

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Much quicker method

This method has the only drawback that the resulting bones won't have a size of one.

3. Snap the cursor to the first vertex.
4. Add a bone (at cursor location).
5. Snap the cursor to the 2nd vertex.

6. Select the head of the bone and snap it to the cursor position.

   

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Bonus Rigging

14. Create the same single bone rigging for all needed triangles.
15. Add a new bone at the center and parent all others to it, this will be the root bone to move the whole rig.
16. Add custom shapes from meshes to the bones.

Now it looks pretty.

A unified open controler

17. Select triangle flap bones. Duplicate the ⇧ ShiftD. Scale the down (just to make the easy to distinguish). Name everything correctly. Parent the larger bones to their smaller parents. The small parent bones are going to be used to control an overall animation of all four flaps. Rotating them will rotate their child bones and the mesh.

18. Create an action on them by selecting the parents and setting a rotation key I > rotation on frame 1. Rotate them outwards RYY on frame 21 and set another rotation key.

19. Rename the action and add a fake user just in case.

20. Add another controler bone and parent it to the root bone. Name it usefully ("open"). Select a parent bone of a single flap and add an action constraint targeting our action with the "open" bone as the driver and the range as the action range.

The "open" bone now controls the action.

21. Remove the action from the dopesheet / action editor.
22. Select all parent bones, selecting the one with the action last. Press space and find/execute the operation: Copy Constraints to selected bones. Then move them to another layer. M2

Simple rig done.

Answer 2

That's exactly what a simple single bone does: it rotates in its own (local) axis, so that its rotation world is affected by its rotation set in edit mode.

If you really need (and I don't think so) the triangle of bones following the panel, you can parent them to a bone set as in my example and use it as the main rotation bone.