A stepper is what you want. An SG-90 servo will never turn the turntable, at least without a LOT of reduction gearing and it would be VERY slow. Also it will only turn partway, not all the way around. There are continuous rotation servos, but a stepper will be the best option.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
You might want to look into a 'stepper' motor controlled by an Arduino Motor Shield. There are lots of circuits/software available to do this(R/C Cars and Battle Bots). The stepper motor allows very precise control of your TT bridge...
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Anyone have suggestions as to what servo to use with the Walthers 90' turntable? It's not an immediate project, I'm just looking into it. The $1.25 Arduino-driven SG-90 servos for turnouts are working great so far.
Julian
Modeling Pre-WP merger UP (1974-81)