Well, there are two. One, the actuator may stick, as it's driven into a mechanical dead end. Two, the actuator arm gets closer to the polar axis as it is extended. Once it becomes so close, the actuator/mount geometry weakens the actuators effectiveness at holding the dish, or "Over Centers". This results in the dish flopping down, and the actuator alone is unable to raise it back up, as the new geometry doesn't allow it. Best to watch the mount/actuator geometry as it's extended. And adjust the limit so you're before the point where the actuator "Over Centers" If you can extend all the way mechanically, without fear of "Over Centering" Set the limit switch just before it hits the mechanical "dead end".