Hi there,
Welcome to the forums.
I've just got round to answering your comment on the blog, and yes you're right about needing a motor driver.
Can I ask why you're trying to use the Pi Co-op? It would be a more 'integrated' solution, although having to wire on a separate motor driver my retake any space gained. If you were looking for more memory (32kb for the Atmega328 as opposed to 8kb for the mini driver's Atmega8) then we also now sell the
Mini Driver MkII which contains an Atmega328. Although unfortunately the pin numbers are slightly different, so the code would have to be changed slightly.
Regards
Alan