Monthly Archives: June 2014

Taranis Smart Trainer Mode using Sticky Switches in OpenTX2.x

Note : this scheme has the instructor using the buddy box


A better Tx with a better Balance Bar

My son is still struggling to get good control of his plane and I reckon it is partly to do with his old buddy box which has poor sticks and no balance bar.

I thought I would make the Taranis the student transmitter and the old 35Mhz Futaba buddy box the instructor “transmitter” – but the Taranis will be transmitting.

I also wanted to be able control the handover from the buddy box and to be able to put my instructor Tx on the ground unattended to hand launch my son’s plane.

Refer to this article about the basics of Taranis and buddy box / trainer mode

OpenTX 2.x and TR1 – 16

This can now be done with OpenTX 2.x because the buddy box / trainer is always transmitting signals TR1 – 16 to the Taranis even if the switch controlling the student transfer is not active – this in effect means that a buddy box switch can be used to control the hand off from instructor to student => the instructor can use the buddy box.

Smart Trainer Switch ( sort of )

I initially tried using the channel 5 switch on TR5 and this worked well but I wanted to try something along the lines of the “Smart Trainer Switch”. This forum post scheme is to transfer control to the instructor when there is a difference in the inputs between the student and instructor. This would allow the instructor to “follow along” with the student but in my ( fairly limited ) experience there will almost always be a difference – for example the instructor may use rudder input whereas the student probably won’t.

So I settled for a scheme where a significant input of the elevator, aileron or rudder will transfer control to the Instructor and it will remain with them until switch 5 on the buddy box is cycled.

Sticky Switch

One of the new features in OpenTX2.x ( maybe 1.9x ) is the Sticky Switch. This is a Logical Switch which is latched into position by one action and then unlatched by a different action. In the example below moving to SA↑ latches the switch and moving to SB↑ will unlatch it. The latching action will last for 3 seconds and will only start 4 seconds after SA entered the SA↑ state.

No latching will take place unless switch SC is in the SC- position


Note that the sticky switch is set by the transition of the trigger and release values into the required state. So for example if SA↑ is left in place and SB↑ is applied then the latch will be reset and SA↑ needs to be removed and re-applied before the latch will set again.

The Scheme

Step 1

Add TR1,2, 4 ( your channels may vary ) to a new virtual channel as shown below. These represent the trainer elevator, aileron and rudder. The throttle is deliberately left out of the equation. Using a channel like this means you can just use one formula to detect stick movement.

In my case Channel 14 now represents an indication of how far the instructor sticks  ( in my case on the buddy box ) are away from their centres.


In my case I only want this feature to work in “Normal Flight Mode”

Step 2

There is no option to use the TR5 signal in the logical switches so it must be mapped to a channel that can in turn be referred to. In my case I am using channel 13



Step 3


Create a Logical Switch ( L9 for me ) that detects movement by the instructor. I selected a value of 25% as all 3 axis are added together and you may have some trim in. Its a matter of trail and error. I also only want this to be active with SG↑ as I use SG to determine the trainer mode I am using.

Then create a Logical Switch ( L10 ) that detects that the TR5 switch ( Channel 13 for me ) has been cycled. In my case it is either +100% or -100% so I used < 10% as a trigger.

Finally create a Sticky Logical Switch that is set by L9 ( Instructor movement ) and reset by L10 ( TR5 switch cycling )

The Result

If the instructor moves their sticks in “Normal Mode” with SG↑ then they get control. If they cycle switch 5 on the buddy box with the sticks centred then control reverts to the student using the Taranis

I was a bit worried that if the buddy lead as pulled out you could be left with no control but it seems to revert back to the Taranis. You should test this for yourself.


Configuring the Taranis Trainer / Buddy Box Functionality


I use an old 35 Mhz Futaba SkySport 6 as a buddy box for the Taranis. It works really well and with OpenTx 2.x you can now also pass through more than 4 channels for things like the flaps.

Initially I used a Phoenix Simulator adapter but just recently I have soldered the buddy lead directly into the Futaba for better reliability. I would recommend using the simple JR lead rather than a stereo lead but opinions on the web seem to vary.

The Basic Concept

The basic concept is simple. The buddy box passes a copy of the output signal to the Taranis via a simple 2 core trainer cable ( that bit surprised me ). The Taranis sees these inputs as Input Channels 1 – 4 ( and more in OpenTx 2.x – see later ).

The inputs can be calibrated and scaled / multiplied. Each of the inputs is mapped to a stick and the mapping can include a weighting e.g. 125% and whether the signal is absolute ( no master input when the student is in control ) or additive where the master and the trainer signals are added together and the resulting sum applied to the model. The second option sounds very clever but having thought about it doesn’t really seem that useful.

Up Front Decisions

Before you start you need to decide on some basic things :

  • If your buddy box has dual rates will you use these with your student or will you use the dual rates on the master ( Taranis ) for both instructor and student ? I prefer to just use the Taranis rates as it is one less switch to check. If you do this then remember to disable the dual rates on the buddy box.
  • You can configure the Taranis to take all of the flight control inputs from the buddy box or just some of them. My Bixler setup has a switch that in one case gives the student full control and in another leaves me with the throttle control.
  • How do you want to hand control across to the student ? I would highly  recommend the spring loaded switch SH but you could use one of the other switches.
  • I would highly recommend a master engine safety be configured as it is very easy to hand control to the student when they have inadvertently added throttle whilst the model is on the ground. A master switch will protect from both Student and instructor inadvertent throttle movements in the pits.

Step 1 – Connect the buddy box

Connect the buddy box to the Taranis via the lead and switch it on

Step 2 – Navigate to the TRAINER menu

Continue reading

FRSky Taranis 6 Channel Configuration eepe with trainer, flaps, crow spoilers, reflex and instructions

Guide to Taranis "Bixler" 6 Channel

This has been superseded

I have had my FRSky Taranis for a few months now and am loving the software side of it. My son has a 6 servo bixler and I have set up a configuration on the Taranis to support trainer ( buddy ), flaps, Crow Spoilers and Reflex – mostly just to experiment.

You can download the eepe file, the sounds and the instruction pdf below. I will be updating it as I go along – probably to OpenTX version 2 very shortly. I will probably blog various sections too.

This version of the PDF > Bixler_6_Servo_Guide_pub_140607

This version of the eepe and sounds => Everyting_Bixler_6_Servo_Guide_pub_140607

The latest version ( what ever that currently is ) can be found here => 

The key features I wanted were :

  • A Motor Safety Switch
  • A trainer function so that I could connect the Taranis to another buddy box via a buddy / trainer lead. I wanted to have two modes – a partial mode where I retained throttle control and a full mode where I could pass across all 4 primary functions.
  • High, Medium and Low Rates with Expo
  • Rudder and Aileron mixing to smooth out turns
  • Flaps with elevator compensation
  • Spoilers / Air Brakes / Opposing Ailerons and Flaps or Crow as the glider folks call it. Also requiring elevator compensation
  • Reflex – positioning the flaps in a slightly up position – supposedly makes for more speed – I just like experimenting
  • A basic “panic mode” that removes all mixes
  • Dangerous functions such as flaps or spoilers should have repeating warnings to remind you they are active.
  • Occasional functions should have a once off voice alert to remind you what they are – e.g. the partial trainer mode selection.