Hello there,
this thread is a little bit older, but the problem is very common for ASD-Tug builders.
One possible solution (proven!) is using a gear motor, driving a worm gear that drives a pretty big wheel.
This wheel is on the turning axis of the Azimuth stern drive / Schottel drive.
When adding a potentiometer with a kind of gear, controlling the turning gear motor with the electronics
of a servo, you can get a very nice maximum angle of turn.
A guy from the netherlands had posted some interesting pics in a german forum. (The guys nick is jan41).
He is the builder of several VSP and ASD Tugs in pretty big scales, building his drives homemade.
Here is a page from a german forum:
http://www.schiffsmodell.net/showthread.php?t=31224&highlight=schottel&page=5and here is a pic:
http://img502.imageshack.us/img502/2517/vikingbank24december200sx1.jpgThe orange gear is for driving the potentiometer.
A source for schottel drives is aeronaut / jedamski in Germany - but they are pretty expensive.
So I wonder if there are drawings for homemade azimuth stern drives.
Best Regards
Holger