Transformation constraint Y-axis bug?

Support Animation and Rigging
#1

I never really know what’s a bug or what’s my misunderstanding but this is suspicious.

Imagine wanting to roll a ball. Simple - Empty and Sphere.

Sphere Copy Location targets the Empty but not Z-axis. Now to make it roll:

Transformation Constraint where Location of Empty’s Y triggers Sphere’s X-axis Rotation, and
Location of Empty’s X triggers Sphere’s Y-axis Rotation. World to World, surely.

Empty’s X makes the Sphere roll correctly but no matter what I have done, Empty’s Y LOC rotates the Sphere Local X

The local X keeps wobbling around since the sphere is rotating correctly on the Y. This should be easy, right?
Is this something to report or is it my mistake?

Attachments

copy transform x yes y no.blend (516 KB)

#2

Can’t open the file but this surely is related to your object’s rotation order. Try parenting your sphere to another object - one will be constrained on x, the other on y.

#3

I’ll bet it’s the spaces in the filename…

Interesting, I’ll try another empty for the second axis. I’ve never heard of “rotation order” but I’ll look that up. Sounds intuitive but I’ve learned not to take too much for granted!

Attachments

XyesYno.blend (516 KB)

#4

Right you were. Known trouble includes not only what I’m trying to do with Constraints but also with bones and their rotations etc…

"For compatability, most tools in Blender should still just use the default XYZ rotation order still when dealing with Eulers. Only tools dealing directly with Object/Bone rotations (bones in particular, at the time of writing) need care to take into account rotation orders of the said parts when performing operations.The following tools/code are most affected:

  • Constraints -> especially Copy/Limit Rotation constraints…
  • Transform -> this is still a bit patchy now (for bones support)

Obviously, PoseChannels and Objects are going to be affected…"

This from: https://wiki.blender.org/index.php/User:Aligorith/EulerRotationOrder

So this simple effect is outrageously difficult. I never would have suspected it. There are two ways to immediately change rotation evaluations for those who need to tinker:

good grief rotation.jpg938×563 111 KB

Cheers! Thanks for the tip too.

#5

Hey, I have not looked at your file, but this link does a very good job of explaining how Blenders rotations work.

https://wiki.blender.org/index.php/User:Pepribal/Ref/Appendices/Rotation