Servo motors are designed to rotate a maximum of +/- 130 degrees. But they can be easily modified to make 360 degree turns. The hack is very well documented for various servo motor models. Here I use a Hitec HS-325HB servo purchased at ServoCity. This motor has a very good torque/size ratio and costs only around 10 dollars.
Remove the screw holding the white wheel on the front of the motor.
Remove the four long screws on the back of the servo.
Remove the front cover of the servo (might require some pressure).
The gears are now exposed. Remove them, place them in a clean place making sure they don't get dusty.
Remove the back cover of the motor and save all the covers and screws in a safe place.