The latest addon for the Raspberry Pi makes it very easy to control enough motors for a robot or anything you care to imagine. The Gertbot is more sophisticated than you might think. 

Gert van Loo, or just Gert to most Pi enthusiasts, is well known for some nice electronics and especially the very capable Gertboard expansion. Now we have the Gertbot which could be described as a way to control four DC motors or two stepper motors, but it is a little more than this.

The board has its own ARM cortex-M3 processor which does all the work and leaves the Pi free to just send it high level messages to get things done. Given that the Pi isn't the most powerful computing device this is really good news. 

It works with any of the four Pi models and, given it works via a serial connection, it can be made to work with other controllers. It was clearly designed before the model A+ and B+ and so it isn't a more modern HAT expansion board, but again this doesn't matter, because of the serial interface and the built in processor. 

From a hardware point of view, it is also very capable. It has four motor drive bridge circuits working at 30V at up to 2.5A and two open drain MOSFETs working at 30V at up to 3A. You connect suitable motors to the screw terminal block and then control them by sending simple commands like "start motor", "stop motor" as hex codes over the serial link. The DC motors can be speed controlled using PWM. 

As a sort of accidental extra, you also get four 12 bit ADC ports, four 12 bit DAC ports and some general purpose I/O lines plus automatic motor end-stops. If you need more than four DC or two stepper motors then up to four boards can be cascaded.

The good news is that you get the software you need to control the motors including a GUI interface that you can use for experimentation. You also get C and Python drivers for your own programs and a DCC GUI so that you can control a model train setup. 

At $64 this motor driver board isn't cheap - almost double the price of a Pi B+, but it is sophisticated and easy to use. If you have a robot or any mechatronic project in mind it is worth considering.  There is a nice example of a four-motor robot on the Gertbot website:

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