UPDATE: Lets Make Robots, my home digital hackerspace, was purchased by RobotShop. I don't want to go into, but the new owners banned myself and most of the veteran members. That stated, most of the links there will be broken. Luckily, I was able to make a copy of my content (the reason they banned me) and moved it to a Github site--it was a hurried move, so the content maybe a little rough right now.
This is not the definitive story on Pi and Arduino orchestration. Just my version.