OpenTx and FrSky

OpenTx is the Open Source version of radio control. It is an operating system for transmitters. The most popular hardware is that produced by the Chinese company FrSky ('free-sky') though others are available. FrSky makes several transmitters and receivers but for Europe the most popular is the Taranis X9D plus transmitter and X8R receiver. Both are surprisingly cheap (£160 and £30) and seem extremely good for robustness and performance. I get mine from RC Life. Whats more you get a free 2000mAh rechargeable battery and charger for the transmitter, which the makers say should give seven hours of run time.

The Taranis X9D plus


Corner showing some of the switches and two of the four rotary controls

X8R receiver showing eight servo ports and the S.Bus


The X8R has eight channels but can be expanded to sixteen by attaching another X8R or by using the socket for the S.Bus serial networking system. It has telemetry by default and includes Received Signal Strength Indication (RSSI) as standard. There are several data sensors available including Lipo battery voltage (essential for serious electric flyers), GPS for height, speed and map location, airspeed, RPM and temperature, motor current, and a variometer for the glider enthusiasts. All are light and compact and are daisy-chained to the SmartPort on the receiver using servo type leads. No controller is needed.

The X9D can be programmed using the transmitter screen or with free 'Companion' software on a computer running Linux, Windows or Mac OS. The setup is uploaded to the transmitter using USB, and can be simulated on the computer before uploading. Download Companion from OpenTx. Transmitter setups can be backed up to a computer.

OpenTx takes a short while to learn. You have to program the transmitter before you can use it. Sticks, switches, rotary controls and sliders are all called 'inputs'. Servos and other controllable devices are all called 'outputs'. The connection between them is called a 'mix'. Mixes are very much more flexible than the usual ones on transmitters and are created and viewed as lines of code. Response curves are easily set up. It is quick and easy to input a standard four-channel system but the software is so powerful it warrants serious study.

Binding is extremely quick and easy and custom failsafe is available and very flexible.

I have reviewed FrSky kit on the Innovations page.

Radio Control Models and Electronics magazine ran a series of articles on OpenTx and Taranis starting with the April 2016 edition.

Most of the FrSky manuals for X9D, X8R and telemetry are here


(C) Peter Scott 2016

Last edit 16 March 2017