OpenTX - Application Note 08
Use the GPS sensor to transmit telemetry to the radio, announce distance from the power up point, altitude and ground speed. Display the data on graphs in OpenTX Companion and display the flight on Google Earth.
The FrSKY GPS (Global Positioning System) Sensor V2 is used to transmit the following parameters to the Taranis radio during flight.
The data is displayed on a radio’s telemetry screen, announced using special functions and logged onto the SD card. The logged data is then displayed graphically on OpenTX Companion and on Google Earth as a 3 dimensional flight over the terrain.
Connect the Sensor to the Receiver
Connect the cable from the X8R receiver’s Smart Port to one of the 3-pin connectors on the GPS sensor as shown in the photo. (The other 3-pin connector can be used to connect to other smart port compatible sensors in a ‘daisy chain’ connection.)
The GPS module must be mounted in the aircraft with the ‘UP’ sticker pointing up in the sky. The GPS antenna is under the ‘UP’ sticker and this must be pointing to the GPS satellites orbiting in space.
When power is applied to the receiver and GPS module, the LED on the GPS module flashes fast until the smart port connection is established. The LED flashes at a medium rate while the GPS establishes GPS lock. It takes up to 30 seconds to lock and the LED then flashes slowly. The data is then sent to the Taranis radio.
Display the Data on a Telemetry Screen
To display the distance, speed, and altitude above ground, on the Telemetry screen select a position on the screen to place the data. Highlight the positions using the ‘+’ and ‘–‘ buttons, press ENT to edit, and use the ‘+’ and ‘-‘ buttons to select ‘Dist’, ‘Spd’ and ‘GAlt’ from the lists.
From a main screen, press PAGE LP to display the telemetry monitoring screens. Press Page SP to display the next screen.
There is, by default, already a telemetry screen displaying longitude and latitude.
Audio Announcement of Distance, Speed and Altitude
The announcement of telemetry data is done using special functions on the Special Functions screen.
When switch SD is up (or down), the announcements are disabled.
When switch SD is in the middle position, the values of the distance, speed and altitude are announced every 10 seconds.
The units are set in the ‘Units’ parameter in the Radio Set Up screen. For example, if the units are metres, the announcements may be as follows.
“eleven metres”, then “sixty kilometres per hour”, then “seven metres”.
Turn Data Logging On and Off.
On the Special Functions screen, use a special function to turn on and off the recording of a log.
When switch SC is up, no logging is done.
When switch SC is in the mid position or down, data is logged every 0.1 seconds and stored in a file called ‘modelname -yyyy-mm-dd.csv’ in the folder ‘LOGS’ on the SD card.
The log file names can be viewed on the SD Card screen.
Audio files can be used to announce when logging is turned on and off using the following special functions.
File ‘lggngoff.wav’ announces ‘Logging Off’. File ‘lggngon.wav’ announces ‘Logging On’.
Refer to Application Note 4 for the creation of files ‘lggngoff.wav’ and ‘lggngon.wav’.
Displaying the Logged Data on OpenTX Companion
Start OpenTX Companion.
On the Taranis radio, run the BootLoader. (To run the BootLoader, push both the horizontal trim tabs towards each other while turning on the radio.) Plug the USB cable into the back of the radio and into the PC. Check on Windows Explorer that the radio appears as a Removable Disk.
On the Log Viewer, click ‘Open Log File’ and find the Removable Disk. Select the log file in the ‘LOGS’ folder and click ‘Open’.
A list of parameters is displayed in a column down the left hand side. The log records are listed in the table below the graph.
To display the graph of a parameter, select it from the list.
Two or more graphs can be displayed at once. After selecting the first parameter, press the CTRL key while selecting a second parameter. The second parameter is added to the graph. Continue with more in the same way.
In the example above, there are three different sessions in the file. This means that the logging was turned on and off again three times on the same day. Each session can be chosen separately in the ‘Fly Sessions’ drop down list.
This graph shows the throttle graph of the first session only.
To change the time scale, tick the ‘X’ Zoom box. With the mouse pointer over the graph, move the mouse wheel and the time scale changes. Click and drag the graph to move it.
To change the amplitude, tick the ‘Y” Zoom box. With the mouse pointer over the graph, move the mouse wheel and the amplitude scale changes.
Displaying the Logged Data in Google Earth.
Google Earth must be installed first. Download Google Earth from here.
The log file is listed in the file tree on the left hand side under ‘Temporary Places’. In this example, the file is called ‘Skipper-2015-02-23’. Expand the tree beneath the file name until the Skipper file is displayed. Double click this file and the view changes to show the flight path as an orange line over the ground. This is a three dimensional plot of the position and altitude of the aircraft during the flight. The view can be rolled, rotated and zoomed using the controls at the right of the view.
The slider at the top left controls which part of the flight path are displayed and animation of the path.
To display the elevation graph, first select Edit, then ‘Show Elevation Profile’.
Move the mouse pointer along the elevation graph and the corresponding position of the aircraft is shown on the field. The cursor is also moved along the elevation graph displaying the data at the cursor’s position.
There are three possible parameters shown on the elevation graph. They are Elevation, Speed and GPS Speed. These can be toggled on and off by clicking their names in the data block above the graphs. Only one or two of them can be displayed at a time.
The minimum, average an maximum values are also shown of each of these parameters as well as other flight data in the data block.
A better idea of the flight path is shown if lines are drawn from the path to the ground. To turn on this feature, first select Edit then Properties. Select the Altitude tab and click the ‘Extend to ground’ box.
Click and drag a section of the elevation profile to highlight it as shown. A red line is also drawn on the map corresponding to the section selected in the profile.