What is the easiest way to get Dragon Balls in Dragon Ball Z Budokai Tenkaichi 3

Go to "Future Peace" in the Android Saga in "Dragon History." Do dragon dashes through the buildings until you see a dragonball appear inbetween the health bars. Then, beat the level and do it again to get more dragonballs.
You won't get the dragonball if you exit the level before beating Cell.