MultiWii 2.4 Fixedwing with Logging

Faced with the desire for a GPS-navigating fixed wing drone, I came upon PatrikE's fork of MultiWii 2.4. I forked it some more, to produce a version with SD card logging. The result is attached to this node.

Here are the high points:

• It is forked from a fork by PatrikE for FixedWing RTH Version 2015-04-31 For almost all relevant information, see http://fotoflygarn.blogspot.com/2014/04/multiwii-gps-airplane.html
• This fork includes SD logging based on wareck's Multiwii_Nav_V2.3 fork https://github.com/wareck/Multiwii_Nav_V2.3 But it uses the current, modern SdFat interface.
• Use with WinGui from EosBandi for setting waypoints. http://eosbandi.com/downloads/
• Since my TX (HK-T6A V2) is impossible to calibrate properly, I have included PWM scaling factor code from http://mifi.no/blog/?p=95 It can be commented out from RX.cpp between lines 131 and 146. Line 130 may also require adjustment. See the link. I hope to develop a receiver-agnostic scaling feature later... we'll see

I am running this software on Mega2560 Pro Mini, but in theory it will also run on atmega328-based FCs with lesser waypoint support. That is probably not true if SD card support is enabled (MWI_SDCARD and related options.) This requires the SdFat Library. (If you do not enable SD card support, it should build without it.)