Hi guys, thanks for checking it out.
Are you sure the fw is installed and running at all? The default Teensy fw also blinks the LED, doesn't it?
Connect a serial adapter and terminal to TX3/RX3 (115200 8N1) to get a command line (like shown in my hookup diagram). There's a number of diagnostics, just type "help" at the prompt. This will at least verify that the firmware is running. "dump" and "timing" may give you a clue about what is going on.
The Mavlink and FrSky default baud rates are correct, unless you changed the AQ default for some reason. Don't mess with FRSKY_BAUD.
For compiling you do need Mavlink headers installed, plus a special include file to fool the idiot Arduino IDE into acting like a real compiler.
All the Mavlink includes you can get from here: https://github.com/AutoQuad/mavlink/tree/master/include
Put the contents of that "include" folder in your personal or global Arduino Libraries folder, in a folder named "mavlink_arduino". Then throw the .h file attached here into the root of your "mavlink_arduino" folder.
Open the MTA.ino project and you now should be able to add "mavlink_arduino" Library to the project using the Arduino IDE. Actually if all the paths match, you might not even need to do that, but it shouldn't hurt.
You'll probably still get a ton of errors, because I don't compile it this way, but it's a good start... j/k, I have tried it that way a couple of times and it seemed to work. Obviously you need everything else installed and configured correctly, like Teensyduino.
HTH,
-Max