As well as being able to control a pair of DC motors, the RRBV2 has some other useful features:

• you can plug a selection of Adafruit I2C displays straight into its I2C socket
• it directly accepts an HC-SR-04 range finder
• it has 2 built-in LEDs
• it has 2 inputs that can be connected to switches
• it has 2 buffered open-collector outputs 

For more information of the RaspiRobot Board V2 and its Python library, see raspirobot.com.

If you want to take your whole Raspberry Pi mobile, get yourself a low cost robot chassis on eBay. Look for one that includes 6V gear motors and wire them up just like the motors we used here.