Rotating 3-D emitter

Question

Hi,
I've got a 3-D emitter: 3D checked, emitter = sphere, arrangement= outline, birthrate 0, velocity 0, initail number = high enough to spread a particles over the surface to clearly indicate a sphere.
When I scrub through the y-rotation (of the emitter) in the properties tab of the inspector, I see in the canvas exactly the behavior I want - it rotates nicely and "appears" very 3-D, even if the group is 2D. Face Camera is checked, although there is no camera explicitly added. However, when I animate with keyframes or rate behavior, there is no rotation on playback. If I select the emitter during playback, I do see its wireframe rotate, but the sphere remains motionless.
In a post on creative Cow back in April, 2008, there is a statement " the only way to get a 3D orbit around of a particle emitter in Motion is by using a camera orbit and having the "face camera" option selected." WHile I understand this approach, it is not what I need for my case since I want two concentric spheres to rotate independently inside of each other. I would be happy just to accept this statement and try to figure something else out. But what is confusing me is why, with no camera and in a 2-D project, when I scrub through the y-rotation of the emitter I see exactly what I want in the canvas (all other elements retain their correct stationary position), but on playback after animating with keyframes or behaviors, there is no animation? It appears all the information is there. Understanding what is going on, whether or not it is possible to animate emitter properties (specifically rotation) would greatly help me out.
Thanks for any insight, Pat

Answer 1

Interesting. I never knew that about particles. Kind of a pain, and not very intuitive if you ask me.
However, there is hope. I figured out what you need to get the move you want. Create a null object (basically a small shape that you turn off). Place it at the center of your emitter. The best way to do that is to create the null and reset it's transformation to place it at 0,0,0. Then reset the transformation of your emitter so it's also at 0,0,0. Enclose them in a group together and move them wherever you need them.
Then apply the orbit around behavior to the emitter. Drag the null into the source well and have the orbit include X and Z axis. Adjust the strength to taste. Make sure that the affects subobjects is checked (it is by default).
Use a clockwise direction for one emitter, and the counter clock-wise for the other emitter. That should get you what you want.
Andy