Bug / Crash Rod dynamic attachment is broken

[Qriva0]

Quaternions don't really "point in a direction", since they're not vectors in R3. A quaternion and its negative counterpart represent the exact same orientation. For an explanation and proof, see: https://math.stackexchange.com/questions...quaternion

Actually you are right. What my dumb brain meant by minus is inversed quaternion. I know quaternion does not point towards any direction, but the way the rod works I expected particle to keep rotation relative to attached object.

Make sure the two attachments don't attach the same control point twice.

This is what I did, I have two different control points attached to that cube, next to each other.

By two attachments I meant one attachment to one control point, and a second attachment to a different control point close to the first. This works because infinite lines pass trough one point in space, but only one line passes trough two points. This removes the ambiguity in quaternion rotation.

To be honest I still don't understand why this does not work. My sense is that quaternion of particle A has some rotation, but because it's driven in different way than static constraint it can get negative quaternion? and because this gives the same orientation, then when it's lerped or weighted or whatever happens there it starts to go crazy? and it only happens when both orientations are aligned? Why it becomes stable after flipping?

In any case I don't understand why it's always opposite direction, for example if I rotate cube by 10 deg, then this is what I get, and it's still unstable.