I have built a arducopter a few years ago end 2012, but I encountered some problems and left it there (and also for other personal reasons) till now.
It was with the APM 2.0 board. Now I’m trying to catch up and I’ve seen that, apart from APM 2.5 e 2.6, there are also other boards around, like Pixhawk and PX4.
So, first question was: can I still run arducopter 3.1 (and 3.2 when it will be available) on my APM board 2.0?
Second question is: how are the 3 boards different (in term of functionalities)?
APM 2.0 can run 3.1 and it will run 3.2 but some features won’t be available, for example EKF (en.wikipedia.org/wiki/Extended_Kalman_filter).
You can post your questions regarding 3.2, in its sub-forum here: viewforum.php?f=100
The difference between APM 2.5 and 2.6 is the APM 2.5 has a built in compass and the APM 2.6 hasn’t.
At this moment the Pixhawk and APM 2.5/2.6 shares the same firmware, so cannot tell a big performance difference between them. But for sure in next firmware releases some of the features won’t be available in APM due to lack of memory and processing power.