[Al Skierkiewicz]

dteshome,
What you are asking to do here is a rather sophisticated setup. With a large arm and the weight you have specified you would need a drive system with low RPM, lot's of torque and some form of brake. Getting the precision you are looking for (about 30 degrees/ move) with the rest of the specifications would require rotation/position sensing and the ability to slow the motor and brake at the location you want. You can of course use some form of indexing so that the motor turns the arm until it hits a mechanical stop. Then you can remove the stop when you want to move to the next position. If you are not concerned with precision you can put a microswitch at each position you want to stop at. Use the switches to interrupt the motor current. Then use a start switch which bypasses the cutoff switches for a time after the motor moves. The start switch is wired so that the stop switches are not part of the circuit until the arm has passed the current position and has moved towards the next position. This would require 12 switches in series, wired for normally closed, and those in series with the motor. The start switch would bypass the series string while pressed and then put them back into the circuit after the start time is over. American Science Center is a good place to get surplus motors, switches, etc. They have a website and are located here in Chicago. I am sure there are stores out by you as well.