Bug / Crash Rod dynamic attachment is broken

[josemendez]

I am confused, how/why quaternion gives the same orientation while it's pointing the opposite direction? I think I am missing something.

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

Also it's not problem with rotation of that object - it's problem with rotation of rod particle, because cube in my case is kinematic for particles.

That makes no difference whatsoever: if two objects A and B are attached, rotating A 45 degrees or B -45 degrees results in the same relative rotation between both. If you statically attach the particle and then make the cube non-kinematic, the cube will rotate instead.

The workaround does not work, it makes rod wiggle like crazy, then randomly stops for a moment when it becomes more stable for several seconds (see attached image).

Make sure the two attachments don't attach the same control point twice. That leads to undefined behavior as stated in the manual:

Particles affected by more than one attachment will follow the attachment that was updated last. The update order for attachment is undefined.

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.

I think dynamic attachment calculates quaternions/matrices incorrectly, because static attachment works correctly (custom script as well).

A static attachment doesn't have this issue because it doesn't involve physics of any kind. A new quaternion is not derived from physical calculations (which are ambiguous because of the aforementioned issue with rotations 180º degrees apart from each other), it just copies the attached object orientation to the particle.

kind regards,