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OpenTx - what is the fuss really about?


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Posted by Biggles' Elder Brother - Moderator on 10/10/2016 23:21:52:

The decoders cost £10.79 each, and the channel changer costs £13.49. So the all up cost of all the kit used in this post was just £35.07 and bear in mind only the decoders will go in the model, the channel changer is a one-off cost as it can be reused again on subsequent models. This FrSky kit is not expensive for the power it gives us I am sure you will agree.

If you are in to SBUS, and don't mind a bit of DIY, you might be interested in using an Arduino Pro Mini as a SBUS to PPM decoder. I've done one and the firmware is here: **LINK**.

This provides all 16 channels in one go, but you will need to aqdd the wires and connectors.

Mike.

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Part of the reason everyone is banging on about open TX is because the hardware than runs it was/is very cheap. A lot of people bought the Taranis who frankly shouldn't have because it was/is really cheap.

The software is actually available to put on to other TXs, of course. What's important to understand is that the software is basically a new version of what was already in existence on the mulipltex profi 4000, which is kind of funny because a lot people were against that TX because it was "too complicated". It wasn't cheap.

If you have used a p4000 successfully you will dive straight in to opentx as it is very similar. Now the problem with the multiplex p4000 was that the internet didn't exist when it was brought out, and the manual was about as much use a chocolate tea pot.

The programming is very powerful, but there are a lot of good TXs about these days. In my view the hitec aurora 9 was a very good TX because it was super easy to programme and also fairly cheap. As I say a lot of people wanted a super cheap tx and got burnt because they didn't like openTX (or didn't understand it).

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Posted by Tom Satinet on 11/10/2016 13:51:53:

Part of the reason everyone is banging on about open TX is because the hardware than runs it was/is very cheap. A lot of people bought the Taranis who frankly shouldn't have because it was/is really cheap.

Well, I think that while there are some people for whom that was true -t frankly I think the statenment "a lot of people did that" is just a little unfair!

There was never any secret about the fact that Taranis used OpenTx, and I suggest many people have sucessfully gone over to it. A significant number of them are on here - and the drone world is full of them where it is very much the Tx of choice!

Also I might point out that while I use Taranis this thread isn't about the Tx as such - its about the software OpenTx - which as you say is available of other transmitters.

BEB

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Posted by trebor on 11/10/2016 16:25:05:

If you purchased one of these transmitters and didn't get on with open tx could you re - install the original fry sky program ?

As Frank says - not an option with Taranis. But frankly without OpenTx, in my view, Taranis would lose a lot - as will Horus. Yes we would still have the low cost 32 channel Rx's etc and all the gadgets. But you can't fully harness them easily without OpenTx.

BEB

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Posted by David Tayler on 11/10/2016 14:24:15:

Great post; could you please let me know where to find the tx template? Also links to buyiny the decoders? Thanks ,David .

Hi David,

if you PM me you email address I'll send you a WORD version of the template.

All the bits I am using can be bought from T9 Hobby sport.

BEB

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I would add that any non taranis users who are interested might consider downloading the Open TX Companion software (free) which allows you to set up and tweak models on your pc, has an in built simulator which shows graphically how the channel outputs react to your control inputs (ir also allows up and down loads to and from your RX via an USB cable)

If you load this you can try out BEBs settings and see for yourself how it all hangs together, at first you will think it strange, then the penny will drop and you say "Ahhhhhhhhhhhhhh of course"

Open TX Companion Download **LINK**

There is also the Open TX University with really helpful videos on everything too (all free)

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Posted by trebor on 11/10/2016 16:25:05:

If you purchased one of these transmitters and didn't get on with open tx could you re - install the original fry sky program ?

Why buy the transmitter? Download the OpenTX Companion and learn to program on that, no transmitter needed, and you can see what is happening with the built in simulator.

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There was never any secret about the fact that Taranis used OpenTx, and I suggest many people have sucessfully gone over to it. A significant number of them are on here - and the drone world is full of them where it is very much the Tx of choice!

Also I might point out that while I use Taranis this thread isn't about the Tx as such - its about the software OpenTx - which as you say is available of other transmitters.

BEB

I've been using Taranis/Open TX/Companion for about two years and think it's the bees knees.

How about a survey to find out what percentage of forumites are using this system versus Futaba, Specky et al?

Shep

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Setting up the Mixes.

In OpenTx the mixes screen is probably the heart of the system. Conventional transmitters tend to have a number of preset mixes for common set ups: V-tail, elevens etc. Then they allow a fixed, often relatively small, number of user defined mixes. OpenTx is very different here, basically we have no predefined mixes, but we also have no effective limit of how many user defined mixes we can have and the system is designed to make them very easy to create and control.

The mixes screen for this model set up is shown below: (Don’t panic! It’s not as frightening as it looks at first glance!)

tar prog 3.jpg

So, what it all about? It’s here that we allocate inputs to channels and mix channels together. So [IN1] – the rudder – is allocated channel 1. The elevator is allocated to channel 2. Throttle to channel 3. And so on.

The master aileron is allocated to channel 4. Now take look at channel 9 – this is the right aileron channel and if you look its set up as a 100% copy of the Channel 4 – ie the master aileron. Similarly channel 13 – the left aileron – is also a 100% copy of channel 4 – the master aileron.

Why are we setting up these copies? Well the fact is channel 4 is just a holding value – it will not be physically connected to anything – there will be no servo lead coming out of channel 4 of the Rx. Channel 4 just passes on its value - from the aileron stick – to channels 9 and 13 for the individual control of the right and left ailerons.

What’s the benefit of doing this? Well it means that if we want to alter something that will effect both ailerons the same – for example add expo or change the throws – then we program that just once into the master aileron and it will effect both right and left ailerons equally. But if we want to make a change to just one aileron – for example fine tune just one aileron’s end points or centre point – then we make the programming alterations on just that control alone, i.e. to change the right aileron only we alter the settings on channel 9 alone. This gives us tremendous power and versatility as we shall see later when fine tuning this model.

This master and copy channel technique is replicated for the flaps and the undercart (gear).

Now there are lots of bits and pieces of programming here I haven’t explained – as I say I’m not doing a programming OpenTx course! But some of it I will explain later and if I don’t and you are interested don’t hesitate to ask and I will try to explain!

Next up – enough of all this theory and setting stuff up – it’s time to connect the wing together and see if it all works - Oh exciting!!!

BEB

Edited By Biggles' Elder Brother - Moderator on 11/10/2016 18:25:08

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Posted by trebor on 11/10/2016 16:25:05:

If you purchased one of these transmitters and didn't get on with open tx could you re - install the original fry sky program ?

You also have the option of installing ersky9x on the Taranis. Ersky9x is another open source firmware that runs on a variety transmitters, and also has a PC program that makes programming the radio easier.

Mike.

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Posted by Biggles' Elder Brother - Moderator on 11/10/2016 18:20:03:

Setting up the Mixes.

Why are we setting up these copies? Well the fact is channel 4 is just a holding value – it will not be physically connected to anything – there will be no servo lead coming out of channel 4 of the Rx. Channel 4 just passes on its value - from the aileron stick – to channels 9 and 13 for the individual control of the right and left ailerons.

What’s the benefit of doing this? Well it means that if we want to alter something that will effect both ailerons the same – for example add expo or change the throws – then we program that just once into the master aileron and it will effect both right and left ailerons equally. But if we want to make a change to just one aileron – for example fine tune just one aileron’s end points or centre point – then we make the programming alterations on just that control alone, i.e. to change the right aileron only we alter the settings on channel 9 alone. This gives us tremendous power and versatility as we shall see later when fine tuning this model.

This master and copy channel technique is replicated for the flaps and the undercart (gear).

Edited By Biggles' Elder Brother - Moderator on 11/10/2016 18:25:08

BEB - sorry to labour this, but do you have to have a master channel to be able to do expo and rates on the control input?, or are expo and rates only available at the output and would have to be assigned individually. The reason I ask is that from what I've seen of Open Tx it's not 100 miles from MPX (Royal Pro/Profi) and in that you input rates, expo, trim step etc etc into the control (input in Open Tx) which then acts as the master to all outputs (Channels in Open Tx) which use that as an input, that way you don't have to sacrifice a channel to be able to fine tune an input in one place. Outputs/Channel are then adjusted in their own menu.

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No master channel required, expo and rates can be handled by either inputs and mixer or both. One finds the way which works best for you/for the model. Outputs on OpenTX configures suntrims, min and max output level, ppm centre etc.

Download the Companion and have a look.

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Exactly Andy.

Frank - one if the beauties of OpenTx is I can apply things like expo at multiple points not just one.

I want to stress a point I made in the very opening post to ths thread - I'm not claiming this is THE way to do this or the best way or ebven better than any other way. I will only tell you its the way I like to do it and it works for me. You might do it differently - and that's fine. You might not like my way - and that's fine. The main point of this thread is partially to encourage people to show what they are doing - however they do it!

BEB

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The Initial Control Test

OK, first thing is to rig the two wings on a stand so we can see what’s going on…

wings 1.jpg

You can see the three servo cables coming out of each wing ready to be connected. They are labelled up of course so I can see which is which. Also note that I have labelled the wings themselves ‘R’ and ‘L’. The reason is that, because they are inverted, the wing on the right is actually the left wing! And vice versa. Its very easy to get confused (well for me anyway!) doing this stuff so, if in doubt, label it!

The next job is to attached the Rx, via the SBUS and the decoders, and that all looks a bit like this,…

wings 2.jpg

All that messy stuff will of course be inside the wing eventually and all you will see is just one servo lead going in. You can just about make out the “spare” channels 12 and 16 dangling there. So now we turn on the Tx and attach a battery to the Rx and test the ailerons, gear and flaps. At this stage we are checking for three things

  1. Are they moving in the right direction?
  2. Are they moving through the right short of range?
  3. Are they moving freely without binding or stalling?

Here’s a little video of the test. Sorry the sound is so poor it was done on my phone and I needed to press something to make it work better – but didn’t! Never mind I’ll explain here beneath the video.

Well, when you have stopped laughing at the back! The long and short of it is everything is basically movng OK, but some of it is moving in the wrong direction! The gear on the left wing (remember that’s on the right!) is working backwards accrording to my switch convention. I like down U/C to be down-switch; up U/C is then up-switch. It’s sort of logical! The wheel on the right (left hand gear) is working the other way and so needs to be reversed.

Looking that the flaps we have a similar problem, except this time it’s the flap on the right wing (appears on the left) that is out of line. I like the flaps to deploy down when I push the slider down and to stow up when I push the slider up. The right wing (on the left) is doing the opposite!

So, the next job is to get back to the programming and make a couple of small changes to correct these little problems. We will do that in the next post. Then we can start using this system to do some real scale modelling!

BEB

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Posted by Biggles' Elder Brother - Moderator on 11/10/2016 17:42:29:
Posted by Tom Satinet on 11/10/2016 13:51:53:

Part of the reason everyone is banging on about open TX is because the hardware than runs it was/is very cheap. A lot of people bought the Taranis who frankly shouldn't have because it was/is really cheap.

Well, I think that while there are some people for whom that was true -t frankly I think the statenment "a lot of people did that" is just a little unfair!

There was never any secret about the fact that Taranis used OpenTx, and I suggest many people have sucessfully gone over to it. A significant number of them are on here - and the drone world is full of them where it is very much the Tx of choice!

Also I might point out that while I use Taranis this thread isn't about the Tx as such - its about the software OpenTx - which as you say is available of other transmitters.

BEB

Sorry BEB I can't agree with you there. If the Taranis was 500 quid and the RXs cost 50 quid each the popularity of opentx would be far, far less. The success is a meeting of an open source software system, the internet and cheap chinese hardware. A perfect storm, but in a good way, if that makes sense.

People have been prepared to go the hard road to learn opentx, because they know they are saving a shed load of money over the traditional top end radios. You don't need opentx to fly a wot4 anyway! Opentx is very good for certain applications (e.g multi rotors).

You see threads all the time about how do you programme the taranis/opentx, and threads asking for EPEE files and other set ups, which just illustrates my point. Like I say now the internet is so popular it helps because people can get information they need. There was never much of a storm about opentx in the mags I suspect, so the popularity must have come from online and word of mouth.

 

anyway, I'm going slightly off topic to where the thread has gone, so apologies.

Edited By Tom Satinet on 12/10/2016 10:45:31

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Posted by Tom Satinet on 12/10/2016 10:42:44:
Opentx is very good for certain applications (e.g multi rotors).

Edited By Tom Satinet on 12/10/2016 10:45:31

Not really all the work in a quad is done in the flight controller, so 4 basic channels plus one to change the gyro settings., my 250 quad is on my simplest radio.

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Posted by Frank Skilbeck on 11/10/2016 19:51:41:
Posted by Biggles' Elder Brother - Moderator on 11/10/2016 18:20:03:

Setting up the Mixes.

Why are we setting up these copies? Well the fact is channel 4 is just a holding value – it will not be physically connected to anything – there will be no servo lead coming out of channel 4 of the Rx. Channel 4 just passes on its value - from the aileron stick – to channels 9 and 13 for the individual control of the right and left ailerons.

What’s the benefit of doing this? Well it means that if we want to alter something that will effect both ailerons the same – for example add expo or change the throws – then we program that just once into the master aileron and it will effect both right and left ailerons equally. But if we want to make a change to just one aileron – for example fine tune just one aileron’s end points or centre point – then we make the programming alterations on just that control alone, i.e. to change the right aileron only we alter the settings on channel 9 alone. This gives us tremendous power and versatility as we shall see later when fine tuning this model.

This master and copy channel technique is replicated for the flaps and the undercart (gear).

BEB - sorry to labour this, but do you have to have a master channel to be able to do expo and rates on the control input?, or are expo and rates only available at the output and would have to be assigned individually. The reason I ask is that from what I've seen of Open Tx it's not 100 miles from MPX (Royal Pro/Profi) and in that you input rates, expo, trim step etc etc into the control (input in Open Tx) which then acts as the master to all outputs (Channels in Open Tx) which use that as an input, that way you don't have to sacrifice a channel to be able to fine tune an input in one place. Outputs/Channel are then adjusted in their own menu.

As has been pointed out since your post there is multiple places to add diff, expo and rates in OpenTX, and you can use these however you like to achieve your goals. However unless you have an insanely complex model that requires 25+ channels that are driving servos or auxiliary systems over RF then the impact of "sacrificing a channel" is absolutely zero.

This is because the Mixer screen actually has 32 numbered mixers (with an additional FrSky module installed in the back the TX can output 32 channels too, so it has to have that many), and each one of these can have multiple lines within it (there may be a maximum number of these, but I've never hit it - it's well over 10 per mixer). In addition each mixer can be used as source for any other - mixer 1 could drive mixer 8, 8 could drive 1, or mixer 32 could be a source for all the other 31 if you really wanted! I tend to set up my models so that all the channels that actually drive a surface or auxiliary system on the model are numbered from 1 downwards, i.e. TAER from 1-4 for a simple 4ch. I then leave a "gap channel" to make it obvious where the output channels stop, then start the "high mixes" that act as inputs to the output channels (Master aileron, camber, snapflap etc).

Couple all this with the fact you can bind RXs in different ways to choose which channels they respond to and you have a) ultimate flexibility in how you choose to setup and wire your model, and b) a huge amount of mixer resources to which 99.99999% of users will never get close to the limit of.

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Hi all,

lots of healthy debate - that's what we like to see. smile Great hobby this that allows so many different appraoches - good stuff.

So, before I post on sorting out all the directions everything is moving in (!) later today I thougfht I'd better just mention sonething that has been at the back of my mind - its not a major issue but it is something you need to be aware of.

SBUS runs at the higher frame rate. I'm far from being an expert in this area but I believe it has a frame time of around 8ms. This faster frame rate is simply passed through the decoders and onto the servos. Digital servos generally have no problem with this. More robust analogue servos are usually OK as well. But you should be aware that limited spec analogue servos can struggle with this as they were designed for the slower frame speed of 16ms or so. If your servos are not up to it the first symptoms, if you are lucky, might be some jittering type movements. But equally I'm afraid the first sign could be smoke!

I'm using HS 5485HB digitals (which are actually programmable) on flaps and ailerons and JR retract servos (well one JR RT88 and one Spekky - long story!) and I'm having no problems at all with them. But you do need to be aware that, whilst the decoders mean you don't need expensive SBUS servos, you do need reasonably robust, good quality, servos.

BEB

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one thing to bear in mind with "high channels", master channels or whatever you want to call them is that you cannot put one channel as the input in to a mixer unless the input channel actually has an input mixer of its own. (you can't on my version of opentx anyway)

so you if you want to put channel 20 as the input in a mixer on channel 1, it won't do it unless channel 20 has something in it already. Sure it wasn't like that on previous versions.

Not sure I see the point in sbus for most models as the converter is heavier than lightweight servo wire.

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