I'm almost to the Air>Motion Path section of the Particular User Guide, but it looks like that's all about controlling particles after they're emitted.
This is actually raising a number of questions.
First, how do I get an emitter to follow a specific path without key-framing every frame. I created a simple point emitter and used some wind X to give the particles some direction. I key-framed three positions for the emitter, thinking there'd be some kind of bezier handles in the comp viewer I could use to make a smoother path, but there's no path visible at all.
Second, how do I get the particles to emit away from the direction the emitter is moving? Like, they go down when the emitter is moving up, go more left when the emitter is moving right, and start trailing upwards when the emitter is moving down again? I guess that would be the motion path thing that I'll get to in the next couple hours. You guys solved the light emitter problem I had earlier today, and I have a suspicion that that's the way this has to be done. With a light emitter. (Also, I just remembered reading something earlier about "orient to motion," have to back track and refresh my memory.
Ultimately, what I want is a circular logo that starts life edge on to the camera, an emitter starts tracing the circle as it rotates to face the camera. I'm thinking an invisible path identical in dimension parented to the circular logo. But how to get the emitter to follow that path, and have the particles trailing away along the same path? That is my question.
PS. Does everyone else spend hours and hours trying to figure out what guys like Dave and Andrew seem to grasp intuitively, or am I just slow ;)
Using Video Copilot 3D Orbit. Got my logo circle, a null, and the particular layer. I've got the emitter rotating around the circle, but what I need is the circle to begin edge on, and rotate toward the camera. When I precomp, the emitter is flat, so when it starts out you don't see any particles. Does that make sense?
you can't precompose the particular layer with the logo. that has to stay 2d...so as w/e you're using (null?) as a position value for the emitter.
as for going the oposite direction. Michael got it right, give something negative to velocity from motion. But I'm not really sure if that's what you want, It will behave more like sparks than a trail.