Simple Motor Question

I tried to find this, but didn't quite. I need to control 4 motors (or other device) that will rotate an drinking cup (with 2 oz) 90*, one time. Think along the lines of adding flour to a cake mix.

I know that I can do this with steppers, but only 2. Would it be as simple as using a small motor, on for 2 secs then off. Use some type of mechanical stop or micro switch ?

Of course I'd use some kind of circuit to drive the motors. Like http://itp.nyu.edu/physcomp/Labs/DCMotorControl

What about R/C servos?

R/C Servos? Can you drive more than 2?

R/C Servos? Can you drive more than 2?

With the right library, yes.
http://www.arduino.cc/playground/Code/MegaServo

AWESOME ! You just made my day! ;D

I know that I can do this with steppers, but only 2.

No you can drive as many stepping motors as you want. Why do you think there is a limit of 2?

I was looking at the Motor Shield

So don't use a motor shield. Roll your own:- http://www.thebox.myzen.co.uk/Workshop/Motors_3.html

Ok, so I think that at least for a prototype, the RC servos are easiest.

The "cup" that I need to dump weights about 60g, the servo would be mounted on the side, near the CG. Initial thoughts are that I would turn the cup directly, but maybe a gear or lever would be more cost effective. The "dump" would be about 120*.

Anyone care to point me to where I can find out (learn) how much torque would be required ? Those 56g motors are pricy.

I use Futaba 3003 servos. I think they're specced at about 40 or 50 oz inch (3.2kg cm) so should easily do what you want. They cost me around 10 UKP each.