I don't know anything about the fusion brain but your project interests me.
Is there a reason why you are not using the time of day and a "map" of the suns path across the sky to precisely position the dish at all times? Then this way it doesn't matter how cloudy it is it would always be pointing at the sun and you wouldn't get jerky movements etc..
I know that most GPS's can tell you when the sun sets and rises so finding the suns path shouldn't be too difficult?
Sorry if that is too far off track.