Changes
/* Beginner guide/links/building */
** Lesson 3: Maintain altitude when moving around
** Lesson 4: Enjoy
* http://www.airgonay.com/forums/showthread.php?4012-FAQ-Choisir-son-multirotor-FPV-pour-d%E9buter
* The most usefull yt channel, guide, tutorial, tests: https://www.youtube.com/channel/UCahqHsTaADV8MMmj2D5i1Vw
* https://youtu.be/gRSPFYlKo58 How to build Retracts for Quadcopters/multirotors
* http://www.tjinguytech.com/charging-how-tos/parallel-charging Chargin two batteries pack
==== PIDs ====
* PID tuning (by IBCrazy): https://www.youtube.com/watch?v=5VXMXwzlNLU
* PID tuning 101 http://iflyquad.com/2016/03/11/the-pid-tuning-guide-short-version/
=== Failsafe with d4r-ii ===