Constrain particles to one axis? I can't figure out how to generate particles on a plane geometry and constrain the random movement of the particles only in the x axis. Any suggestions? Couldn't find anything on youtube or google. Thanks.
By default a particle emitter has some velocity relative to the normal of the emitter and is affected by gravity.  You can turn the normal velocity to 0 and turn off gravity, and then use the Object Aligned velocity to do what you want.