diydrones/ardupilot — pull request #1287 by NullVoxPopuli (2014-08-05 13:37:18+00:00)
Title: Copter: Added support for V-Shaped and A-Shaped VTail Quadcopter frames

Motors 2 and 4 were reversed for the VTail frame

On my copter, I've had to switch the ESCs connected to outputs 2 and 4 to get the quad to not yaw out of control.

here is another case where someone was experiencing the same thing (see comments):
https://www.youtube.com/watch?v=bDg1B12SxwA

Tim Anon experiences the yaw problem, and after upgrading to the latest beta release, he still has the yaw problem. After he switched outputs 2 and 4, his quad flies normally.

I think the initial flipping was due to the "A" Tail frame, which is what a lot of people call VTail, but the motors aren't inverted. (Like the Flite Test "VTail")

If we want to support both frames, it would be pretty easy. FRAME 5, could be this very motor mixing, but with the motor mixing prior to this Pull Request.

Here are pictures of VTails:
Inverted Motors:
![fczea7k](https://cloud.githubusercontent.com/assets/199018/3294967/43336fa8-f5b4-11e3-8825-467980fee417.jpg)

Non-Inverted Motors
![maxresdefault](https://cloud.githubusercontent.com/assets/199018/3294984/aa0c95ce-f5b4-11e3-86df-248aae518340.jpg)

A Tail:
![v-tail-still001-jpg_1373302916](https://cloud.githubusercontent.com/assets/199018/3294995/e4d3b854-f5b4-11e3-927b-ab4e53d48778.jpg)

There is super interchangeability with the terms ATail and VTail, but I just look at the shape that the props make when spinning.