Example of rotating an object, not camera, using quaternion rotation.
I was looking for ways to rotate an object, not the camera, in a 3d scene using a trackball like control. I found code on StackOverflow which was very close to what I was looking for. This is that example code updated to work more like I wanted.
The rotation now works as I expect. Phew.
Now with momentum Try spinning the cube fast.
Putting this code out there in case it helps anyone or could be improved.
View an example here: http://projects.defmech.com/ThreeJSObjectRotationWithQuaternion/