Adafruit Continuous Rotation Servo - FeeTech FS5103R rotates fully forward or backwards instead of moving to a position. You can use any servo code, hardware or library to control these servos. Good for making simple moving robots. Adafruit Continuous Rotation Servo - FeeTech FS5103R comes with four different horns.
To control Adafruit Continuous Rotation Servo - FeeTech FS5103R with an Arduino, we suggest connecting the control wire to pin 9 or 10 and using the “servo library” included with the Arduino IDE. Position "90" (1.5ms pulse) is stop, "180" (2ms pulse) is full speed forward, "0" (1ms pulse) is full speed backwards. They may require some simple calibration, simply tell the servo to 'stop' and then gently adjust the potentiometer in the recessed hole with a small screwdriver until the servo stops moving.
Example Sketch: https://www.arduino.cc/en/Tutorial/Sweep
Adafruit Web Site: http://www.adafruit.com/products/154