The motor shield is based on the L298 , it is a double complete bridge driver designed to drive inductive loads, such as relays, solenoids, DC and stepper motors. 

This module is based on the popular L298N H Bridge DC Motor Driver . The circuit will allow you to easily and independently control two motors up to 2A each in both directions.

Full size 2 wheels package with rubber base - 125 mm in diameter and 60 mm wide .