My first PixHawk (PixRacer) build starts here.
FRS FrSky S.Port
This should enable a lot of Telemetry to now run over the FrSky's 2.4ghz main link/channels, instead of using a dedicated SiK telemetry radio (for example).
On FRS connector, connect both signal lines together, and then connect to the S.Port line at X8R. Also, connect GND (black wires) but NO RED (Power) WIRE (X8R is already powered by PixRacer through RCIN connector).
Upgrading Tarasis to OpenTX v2.2.1
I had to upgrade my older OpenTX version before the newer "Discover Sensors" was even available for use on Taranis.
It seemed to work fine going from old Open-TX v2.0.12 all the way up to v2.2.1 (all at once) on my FrSky Taranis X9D. Rememeber that you must also upgrade your OpenTX Companion for Windows to version 2.2.1 (so they match exactly):
I followed DKEmxr's forum-post instructions and also some tips from Oscar Liang at this page. I backed-up first, but luckily, I didn't seem to lose any existing models or programming.
As I recall, I used these Settings in OpenTX Companion v2.2.1:
FrSky Taranis X9D (specify exact model)
en (English for me)
lua and luac (only those checked, I dis-liked the way sq5font looked, so i re-did it)
AETR (what ArduCopter uses)
IIRC, I also erased the SD-Card and loaded a new set of files from sdcard-taranis-x9-2.2V0013.zip
And finally toward the end, I found and reinstall Amber (for Open-TX v2.2.x) .
Ok, now all it right with the world :)
With Open-TX v2.2.1 installed, now the "Discover Sensors" option is actually there. But so far, it reads RSSI (for RX) and RxBat (the default ones).
In Mission-Planner, the PixRacer's FRS (FrSky) port is Serial-4. So, set Baud = 57 and Protocol=4. Save that and Reboot PixRacer. Now, when you Discover-Sensors on Taranis, many (all ?) should now populate the List of Telemetry Sensors.
In the Model's Telemetry screen, you can assign Sensor fields to Main Page Flying Screen.
PixRacer ESP8266 WiFi Module
Since it's not "keyed" be careful to always connect like this little WiFi board this way. Be sure it's turned like this, and always use the 8 right-most holes.
On mine, the SSID was "AI-THINKER_code" by default. This is a good sign that the firmware is out-dated. While I could connect the laptop's WiFi to it, I was unable to establish a connection through it with Mission-Planner. DKEmxr says this tiny ESP8266 must be flashed with better firmware before it will work properly.
It apparently must be flashed to v1.1.1 (or maybe at least v1.1.0) . I used NodeMCU-Flasher. It will set SSID to "PIXRACER". It will also set the ESP8266's WiFi AccessPoint to be password-protected now (pixhawk). After running it, you should (might) be able to do further Firmware upgrades "Over the Air". While working with NodeMCU, it might help to disconnect from Internet and connect laptop only to ESP8266 SSID (AccessPoint/ HotSpot) via WiFi.
If your FTDI-wiring is correct, but you have trouble getting NodeMCU-Flasher to work, try swapping the wires for TX and RX (nothing should blow or fry just swapping those two lines). This ended-up being the reason my ESP8266 couldn't initially get MAC addresses in NodeMCU (and finally initiate the Firmware Flashing process). I followed the (simple) cable pin-out exactly so I think that maybe the silk-screened TX and RX labels on my new 3.3volt FTDI-USB Interface might be incorrectly swapped-around.
Communicating with PixRacer using Mission-Planner over WiFi (ESP8266 Module)
In the top right corner of Mission Planner, choose UDP. I don't think baud rate matters. Click the CONNECT button. If it asks for the Local port, enter 14550.
While I haven't tried it yet, I've read that it also works with QGroundControl.