In this movie, we chose to use 14 generators, but we fixed 4 of them, allowing the others to move as usual. The four fixed generators were placed in a sort of hooked barrier. The remaining generators were given random y coordinates, but were all forced to lie on the right hand side of the barrier (by giving them an x coordinate of 8). The animation gives a dramatic picture, in which the free cells press past the barrier to fill up the "low pressure" area behind the obstacle.
We saved a PPMB file containing an image of each step, converted these to JPEG files with consecutive file names, fed that into QuickTime Pro to create an animation, and saved the result as an MPEG-4 file.