I was discussing this once with a guy who used to build planes for a former TOC pilot. While he never tried this he said if you remove one of the wires from the pot on the servo (which one I don't know) the servo will turn indefinately. What he said to do is use a long piece of threaded rod attached to the output shaft of the servo, then put a micro switch on each end of the rod so that the balast weight hits the switch at the ends of rod, thus stopping the servo. How it's actually wired I don't know but it seems like it could work. I always thought to avoid adding extra weight, why not just use the Rx battery(s). Just make sure there is enough extra extention so the wires don't pull the connectors apart when the batteries are traveling down the worm gear (boy wouldn't that suck). In theory it seems like it could work but not sure in practicality.