Open UHF Long Range System for RC – Installation

Open_LRS_1W_JR
Orange LRS 1w Transmitter for JR/Turnigy

A set of inexpensive transmitter and receiver UHF long range system (LRS) has been configure to be used in an FPV airplane provided with an Arduplane controller ( web project ) for Return to Launch and many other functions. The hole project is based in an open source project named OpenLRS (project web)  that offers custom hardware and software to offer inexpensive long range systems.

In my case, I have used a parallel project named “Ultimate LRS” (Link), that offers a PPM channel to control your airplane servos and a Telemetry channel with a single transmitter and receiver. I used two of the the Orange LRS 1W transmitters from Hobbyking, and the total cost has been 2 x 30$, very affordable!. Following the modifications and installation will be explained.

Important Notice

These Long Range Systems are capable to use radio frequency transmissions and output power that may be not allowed in your country. Please always check your local RF legislation to set the frequency and output power according with the regulation.

These systems usually fall under the LPD433 regulations that are part of the ITU region 1 ISM band for licence free communication devices, check the link.

A good webpage for RC frequencies allocation is UKRCC.org. For instance, in Germany UHF frequencies for RC could be used by operators that posses an Radio Amateur License only.

A general rule for RC aircrafts is that they must be controlled always under sight of view, check your RC regulation to keep up to date with regulations.

The installation

In the project website www.itluxembourg.lu you will find most of the information about how to configure and download the custom firmware into the two transmitters. Here I will show you the general steps that I follow in my configuration.

DSC_1255 The first step was to make a hole in one of the transmitters to program the firmware. The Ultimate LRS update v.07 was used to program the firmware version 1.06.
 DSC_1253  The plastic box for the receiver was removed and the firmware for the receiver was upload using the same software. Then I switched on the TX and RX and could check that LEDs in both units indicated that the system was working.Also I used two USB to serial cables to check that the Telemetry data was working. I had problems to know the correct serials speeds, but after using 115200 for the TX and 19200 for the RX, I could send and receive characters from both devices.I used an oscilloscope to check the PPM signal, and move the TX sticks and check movements in the PPM signal.
 DSC_1256  To removesome unnecessary weight and space ( and because it looks cooler) some connectors were removed and the push button.Then cables were solder in the back to connect the GND, VCC, TX, RX and PPM signals to the APM controller.
 DSC_1260  A piece of PCBFR4 was used to offer support to the RF antenna connector and the board was installed in the top of the Skywalker body, the cables were connected to the APM controller, check next image.I have used a Turnstile UHF antenna mounted in the wing bottom part,  Link to the antenna construction
DSC_1261 In this picture you can see the Crius AIOP used for the Arduplane firmware, also the miniOSD board and a uBEC controller board for the video TXT.

 

There is a possibility to download the source code, in case that you need to modify for example the frequency or the output power, check the “config.h” file for modifications.

 Important notes:

  • You must configure in your airplane APM board the serial port speed to 19200 bps.
  • In the computer, you need to configure the serial speed to 115200 bps.
  • ALWAYS check your regulations for RF frequency and power requirements.

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