Hi Chris,
Check out
http://www.dppobservatory.net/DomeAu...DomeDriver.htm
As a suggestion stick to 12/24v rather than 240v, to change the speeds as you mentioned earlier at 240v requires an inverter module (read expensive), necessitating the use of a three phase motor. Unless the dome you have is nearly impossible to move by hand, a small 12 or 24v will do the trick, and if you need to use the power of a 240v motor, a friction drive will more than likely slip.
Brett