you use another magic gearbox to drive the control shaft. then you use another magic gearbox to control that gearbox. the control has to be as powerful as the input (or even more powerful if it is geared down). whenever i see something like this, that is so obviously wrong, i wonder why they don't ask a professional. but i think, perhaps, they do ask a professional, who tells them it won't work, so they ignore the professional.