Dropix/Pixhawk Integration

September 16, 2016 11:41 am

If you are using PX4 firmware, follow their tutorial here. Otherwise :

  •  Base setup 

In order to set up modules, you first have to download U-Center here. Once installed, connect your base module with a USB cable to your computer. Remember that the board equipped with NEO-M8P-2 is capable or both base and rover functionalities and that the other one (equipped with NEO-M8P-0) is only capable of rover functionality. So make sure to use your NEO-M8P-2 board.

Click on the menu to select the port corresponding to your Tiny RTK Base.

Tiny RTK Drotek M8P Ublox Pixhawk Connection

Now go to View -> Configuration View and slide down until you see the MSG (Messages) menu. There, open the menu and slide down until you see RTCM 1005. Check both UART1 and USB and click on Send. Repeat the operation for RTCM 1077, RTCM 1087 and RTCM 1127. Also activate SVIN message through USB only. It is important that you click on Send each time, otherwise your changes will not be stored in the device!

Tiny RTK Drotek M8P Ublox Pixhawk Connection

Tiny RTK Drotek M8P Ublox Pixhawk Configuration 2

Tiny RTK Drotek M8P Ublox Pixhawk Configuration 3

RTCM is a standard protocol created to transmit GNSS data efficiently. Message 1005 contains base position, while 1077, 1087 and 1127 contain GPS, GLONASS and BEIDOU raw data respectively. It is important to check both USB and UART 1 because depending on configuration we will be sending those messages either from USB or from UART 1. SVIN (Survey-in) is a message that provides base position calculation status. Keep on mind that you need to know your base’s position quite accurately in order to compute a precise RTK position for your rover. If you have no precise position you can use the built-in Survey-in mode, that will average a classical GNSS position over time until you reach a desired accuracy.

Then move to TIMEMODE 3. There you can choose between the Survey-in mode (if you do not know your base’s position precisely) or the Fixed mode if you know them (either in ECEF ot lat/lon/alt).

Tiny RTK Drotek M8P Ublox Pixhawk Timemode

In Survey-in mode choose a minimal survey time and minimum precision and click on Send. You can then go to View -> Messages View and Scroll down to SVIN message that will provide you with the real time status of the survey. Once the survey finished, the board will automatically enter Fixed mode with the calculated coordinates. The board will re-enter Survey-in mode at each start up.

Tiny RTK Drotek M8P Ublox Pixhawk Survey

In Fixed mode enter your coordinates in ECEF or Latidude/Longitude/Altitude system and click on Send.
Tiny RTK Drotek M8P Ublox Pixhawk Survey 2

Now you have to choose between :

a) Encapsulating raw data in your telemetry link

 

Basically you only need to use the USB connection between base and your ground control station. At this point you only need to save your configuration bit hitting CFG (Config) menu, selecting all memories and click on Send. Your whole configuration is now saved.

Tiny RTK Drotek M8P Ublox Pixhawk Save

Now move to your ground control station and inject differential data into the telemetry stream. In Mission Planner this can be achieved by hitting Ctrl + F and selecting the Inject GPS function. Select the COM port corresponding to Tiny RTK, select 9600 as baudrate (actually the value does not matter because it is a USB connection) and click Connect.

Tiny RTK Drotek M8P Ublox Pixhawk Mission Planner

b) Using a dedicated link

That means that Rover port will be connected to your flight controller’s GPS port and Telem port will be connected to a datalink directly linked to your base. To enable this feature you have to match your datalink’s baudrate with UART 1. Go to PRT (Port) menu and select a baudrate (usually 57600). Click on Send.
Tiny RTK Drotek M8P Ublox Pixhawk Port

At this point you only need to save your configuration bit hitting CFG (Config) menu, selecting all memories and click on Send. Your whole configuration is now saved. Now plug your datalink to Telem port.

Tiny RTK Drotek M8P Ublox Pixhawk Save

  • Rover setup

 

Rover’s configuration is slightly different than base configuration. Blue LED indicates power, green LED flashes every second whenever a fix is acquired, red LED is off when no differential data reached the device, blinks when the solution is float and is solid when the solution is fix.

a) Encapsulating raw data in your telemetry link

 

For this feature the soldering bridge on the board needs to be activated (soldered). Then connect Rover port to your flight controller’s GPS port. Your flight controller will automatically configure your Tiny RTK. Differential data is streamed through GPS port, so you are now ready to go.

a)Using a dedicated link

 

You need a special configuration for this feature. Soldering bridge must be disabled (unsoldered). First connect your rover to U-Center with USB just as you did with your base. Go to View -> Configuration View and select PRT (Port). There make sure to select your flight controller’s GPS baudrate (38400 for Pixhawk) and click on Send.
Tiny RTK Drotek M8P Ublox Pixhawk Port

This baudrate has to be selected manually because there is no link between your flight controller TX GPS port and Tiny RTK RX port, so it cannot be configured automatically at start up.

Frequency must also be adapted. Go to RATE and enter 200 ms (5 Hz) and hit Send.
Tiny RTK Drotek M8P Ublox Pixhawk Frequency

Also go to MSG (Messages), disable all NMEA messages (uncheck all the boxes, do not forget to click on Send for each message).
Tiny RTK Drotek M8P Ublox Pixhawk Messages

You have to repeat this operation for all this NMEA messages : GGA, GLL, GSA, RMC, VTG, GST, ZDA and GNS.

 

Activate the following messages for UART 1 (check the box in front of UART 1 and click on Send for every message) :

  • NAV-POS-LLH
  • NAV-STATUS
  • NAV-SOL
  • NAV-VELNED

Tiny RTK Drotek M8P Ublox Pixhawk Messages

You can also set the dynamic filter on Airborne 4g in NAV5 tab.

Tiny RTK Drotek M8P Ublox Pixhawk Dynamic

At this point you need to save your configuration bit hitting CFG (Config) menu, selecting all memories and click on Send. Your whole configuration is now saved.

Tiny RTK Drotek M8P Ublox Pixhawk Save

Now you can unplug the USB and connect Tiny RTK to your flight controller using Rover port and to your datalink using Telem port. Make sure your datalink is also configured to work at 38400 baudrate on rover side!