With a standard sized servo and included 38mm diameter wheel this unit makes for a very low cost robot drive system. Combine two units to create a full differential drive system with speed and direction control.
Looking for a quick & cheap robot drive? The S04NF continuous rotation servo and included wheel from Dagu is low cost way to get your robot moving.
The servo is factory built to run continuously rather than move back and forth like a normal servo. The speed and direction of the wheel is controlled by normal servo PWM control from a microcontroller or RC receiver. This makes it very easy to get going. The servo just needs power (4.8-6V), GND and a signal wire to your controller. The servo has its own motor driver inside!