Saturday, February 7, 2015

OpenTX, the ultimate F3x radio firmware ?

After leaving the Team JR as an official pilot for 3 year, I was again on the radio market to find the radio that would fit my needs.

My requirements were quite simple: I needed a very flexible programming allowing to implement in flight adjustements. For exemple, I wanted to change the snap flap rate with a clic of trim, per flight mode, or I wanted to change the ailerons differential with another trim, change the camber with a knob, change the elevator compensation with butterfly in a trim clic, etc ... So Flexibility first, but not only, I also wanted an easyly upgradable radio, a good choice of receiver with small size for tiny F3X fuselages, voice capabilities ...

After studying user manuals, I have identify the Jeti DS/DC, the Weatronic Bat 60, the FrSky Taranis, and possibly the T18MZ . Most of these radio are high end radio, so the entry ticket is quite expensive. If you add the price of 5 or 6 receivers, then the investment start to be really high.

And the winning Radio is ?

I finally decided to give a try at the FrSky Taranis/OpenTx. I heard a lot of people talking about it, saying that it was a unique radio aith a real programming power, and at a cheap price.

to be honest, I have not been disapointed ! There is no better definition of a limitless programming with the Taranis/OpenTX ! Yes, the transmitter is a bit plastic compare to the Jeti or some other brands, but electronics is clean and reliable. Sticks are good quality and smooth.

I selected the X6R receiver as it has the right dimension for our tiny fuselages. I use the S-Bus input to power it, so I have 6 servos outputs.

I must admit that the learning curve is quite hard. In fact I spent lots of time studying, reading, watching video, exhanging with Taranis Owners who shared there template. Michael Shellim articles  and my F3F mate JB Deguelle advises helped a lot.

And one day, I just had a sort of revelation and everything became cristal clear, the programming logic was simple and obvious. Then I restarted from scratched and created my F3F template featuring the following in flight adjustements:
  • Snapflap rate per flight mode, using the throttle trim, so I can increase or reduce the rate.
  • In landing Fligh Mode, this throttle trim can modify the elevator compensation when deploying butterfly
  • Ailerons differential using the rudder trim
  • Thermal camber adjustment using one Knob
  • Elevator throw adjustment using the second knob

And this is just a start. Absolutely evrything is possible, no limit, not lock, no compromise !
I just regret that there isn't 2 additionnal digital trims, it would have been perfect because the digital trim position is per flight mode when the knob position is analog so is global for all flight modes
The Pair OpenTX / Companion TX is just perfect to program, backup, upgrade, etc ...

LUA scripting

And there is these famous LUA scripts !!!!!
Imagine that you can code (with little knowledge) everything you dream ! For me it has been the case. I wanted to develop an F3F practice chronometer simulating an entire F3F run, with the 30s to gain altitude, with late start management, or early start with a switch. Every 5s there is a vocal annoucement (I used AT&T text to speech webpage to create the vocal files). Then it chronometers the run, but you have to count the number of laps yourself. When stopping the chronometer, it stores the time (6 memories) and keep the best time since the radio has been switched on. Just the ideal tool to practice, compare settings, compare planes, and train, train, train ...
I started from another script from Michel (on4mj) for F3K. I kept some timer mgt functions, display layout. I suppressed all the F3K tasks mgt, and simplified the main function as my requirements were much more basic. (Thank you Michel for your expertise, and detailed answers to my questions).

Does it work ? Yes ! Have a look to my video below.
I will very soon publish the source code and provide the sounds files to the F3F and Taranis community.
Weather being bad, I have not flown with my Taranis yet. Hope I can do it soon.


  1. Dear Pierre
    Nice report on your search for a flexible radio solution. As I am not so sure, if I ever could reach an appropriate level to program a Taranis, I would be intersted to know also, which radio did end on place to.
    Your preferences are very interesting also for me, especially the option to change snap flap and butterfly compensation with trottle trim depending on flight mode.
    Thank you very much for sharing so many of your experiences in your blog.
    Best regards, Christoph

    1. Hello Christoph,
      In second place I would put the Jeti. But the weight of the transmitter is high 1.3kg so not very adapted to walk in mountain. In third, the Weatronic. The only suitable receiver is the Smart 8, which is a bit big compared to Jeti or FrSKy receiver size, so will not enter in all fuselage.
      hope this answer your question.

  2. I'm waiting for the new Frsky Horus: or the 9Xe

  3. I am sure that making count the lap by the taranis is not a big deal ;)
    Nice review to read from you for a Taranis lover like me.

  4. Congrats Pierre. I agree about the lack of trims... however, there is a way of overloading any of the four trim levers under the control of a switch - so they can both (a) update GVARs, and (b) act as regular trim levers. I've posted the solution on OpenTx Clinic, see 'overloading trims'. The solution came from Dinamich (one of the devs).

  5. Pierre, you say you are missing additional trim switches on the Taranis. But do you know that you can use one trim switch to adjust several global variables and still use it as a normal trim?

    Read and

  6. Bonjour Pierre,
    Une solution serait de remplacer un des inters 3 positions par un inter "fugitif" (ressort pour le retour au centre) ansi tu peux affecter des fonctions incrementales et decrementales sur des variables globales. Cela t'évite de détourner tes trims.
    J'ai crée un post sur la personnalisation de ma Taranis pour une utilisation plus typée pupitre:
    Merci pour ton blog véritable Référence technique du planeuriste!
    Snowroro alias Romain