I have just published Part 2 of this series, designed to develop skills in Python and ROS so as to achieve flexible control of a UAV. It's based on a Pixhawk FCU with Raspberry Pi companion computer. The Pixhawk is running PX4, but it would also work with minor modifications with Arducopter.
I have also re-released Part 1 with some important updates (necessary due to recent changes in ROS).
We are heading towards a system that will fly autonomously and recognise and track objects in it's vicinity using some machine learning.
Part 2 is on my blog site here. I hope some may find it useful!