All EZB's are microcontrollers, this includes EZ-Robot EZ-B v4 and Arduino. Microcontrollers are computer chips or integrated circuits. Those integrated circuits do not have the "power" to provide current to things like electric motors and relays. That is why Transistors and H-Bridges were invented. A Transistor can provide a large amount of current which enables things like DC Motors to be powered.
In the case of connecting a microcontroller to a DC motor, a device called an H-BRIDGE (sometimes called Motor Controller) is necessary.
An H-Bridge is an electronic circuit that enables a voltage to be applied to a motor in either direction. It's triggered by TTL signals from a microcontroller, such as any EZ-B. These circuits are often used in robotics and other applications to allow DC motors to run forward and reverse.
You can purchase H-Bridges of various types that each provides a different amount of current. The current is how many AMPS a DC motor requires.
2 Channel 2.5 amp HBridge from EZ-Robot
A Dual H-Bridge (such as the EZ-Robot 2.5 Amp H-Bridge) controls 2 motors and can be connected to an EZ-B by 6 digital signal wires. 2 wires control each motor, and 2 wires are for PWM. PWM signals control the speed of each motor.
Sabertooth HBridges come in a variety of types for amperage for different applications. The great advantage to a Sabertooth motor driver is they require fewer wires than a general H-Bridge, such as the EZ-Robot one.