OpenTx - what is the fuss really about?

[Martin McIntosh]

Watching this with interest. After having my set sitting in its box for far too long I took the plunge and successfully test flew four Rx`s in different models. Luckily I have a local club guru to guide me since I got into a horrible mess with reversed trims and timer problems. The timer issue has yet to be resolved. The count down stops after five minutes although the timer on screen continues to run.

Hopefully some of these simple things will be discussed at a later date. I also hope that the content does not get so complex so as to put off novice Open Tx users such as myself, although I would be interested in things like u/c door sequencing and four servo glider wing set ups since my trusty old DSX9 is rather limited in this respect.

[Bob Cotsford]

Posted by Tom Satinet on 12/10/2016 14:19:16:

..............

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

For me it's the choice between multiple plugs to connect when fitting the wing and just one or two.

ps - servo choice - I've had some budget 'digital' servos turn up their toes when driven by Sbus.

[Mike Blandford]

BEB: The SBUS decoder using an Arduino I referenced outputs servo pulses at 18mS intervals, so is fine for analog servos.

Tom: If you have a wing with many servos, then, as Bob says, it is much easier if you only have a single connection to make.

Martin: You might try doing a 4 servo wing setup yourself, you will learn quite quickly doing that. Probably the main thing to 'get your head round' is to look at each channel, choose what you need to control it, then add a mix or mixes on the channel to provide that control.

Mike.

[Andy48]

Posted by Tom Satinet on 12/10/2016 14:19:16:

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.

Been puzzling over what you meant by this, but this is exactly what should happen. If nothing is assigned as an input into channel 20 then the mixer will do nothing. You must always assign some input to a channel before anything will happen. Nothing to do with high channels. Logical when you think about it.

[Martin McIntosh]

I too am not keen on relying on one wire to control everything since I lost a good model when a satellite Rx possibly failed on my JR - same idea really. I now prefer to use multi plugs to simplify connections and supply power individually to the servos. Two 12 way connectors will suffice for eight servos and do not require any safety clips. Much simpler.

When I progress to more than eight channels on the Taranis I shall try 2x X8R Rx`s.

[Biggles' Elder Brother - Moderator]

Getting the control directions right!

Let’s start by fixing the flap on the right wing that is going the wrong way. This specific flap is on channel 10 now we could go to the output tab in Companion shown below,….

On this tab we have the end points, subtrims, what curve (if any) is linked to the output and direction of each channel. We could fix the problem by simply selecting ‘INV’ in the drop down menu in the Direction box that is arrowed. And that would work, fine. And many people would do that. And there’s nothing wrong with doing that!

But, it isn’t the way I want to do it. I want to do it on the mixer tab – I’m awkward like that! Let’s first look at how I can do that, then I’ll try and explain why I like to do it that way.

The picture below shows the mix as it was – when the right flap is going the wrong way. I’ve highlighted the appropriate line.

This is just the mixer we saw before – no change. You can see that channel 10 is a plus 100% copy of the master flap channel (channel 7) which is simply input IN6 – i.e. the left slider. So to reverse what is happening we just reset the mix to not plus 100%, but to minus 100%. And job done. This is shown done below with the red arrow highlighting the change,….

We can fix the left gear, on channel 15, in exactly the same way. If you examine the two previous pictures you will see that the weightings on channel 15 have all changed sign in the second image.

So, to show that everything is now working in harmony and the right way round here is a video,…

Now the obvious question – why do I like doing this in this rather convoluted complicated way?

If this was simply a straight through control – no mix – that was going the wrong way, then I would servo reverse it on the output tab. Because in my world the ‘fault’ here is with the servo igoing the wrong way – so fix it in the servo output tab. Right?

But that’s not what is happening here. The servo is moving as a result of the mix – it is the mix is that is wrong, not the servo. So it’s the mix we should fix – on the mix tab – not the servo. Geddit?

Now just to be very clear – I am NOT saying “you must do it this way,I am right, all other methods are wrong”. I’m just saying this makes sense to me and it’s how I like to do it. You do it your way!

One of the things you do have to be a bit careful with in OpenTx is the fact that you can change these things at so many different points; at input, at mix, at output etc. This is great and gives you a lot of power, but if you are not careful you can end up unreversing something an early tab reverses and then reversing it again later still! (Ask me how I know that is possible!) So I think it’s good to have a bit of a private convention for where you want to do various things. It’s your rule – it doesn’t have to please anyone else, but if you stick with it it will make finding any little programming bugs a lot easier. So for me in this case, if it’s wrong way because of the servo geometry, change it on the output screen; if it wrong way because the mix is wrong – change it the mixer screen. Seems logical to me!

Notice that we made these changes at the lowest control element level – i.e. on the specific right flap on channel 10 and the left gear on channel 15. Suppose one aileron had been going the wrong way – let’s say the right one. We would have fixed that by changing the mix for specifically the right aileron on channel 9. Ok? Similarly if the left aileron had been going the wrong way – just it alone – then we would have altered the sign of the 100% mix on channel 13 the channel that only deals with the left aileron. Yes?

But what if both ailerons were going the wrong way? Well we could make two changes to both channels 9 and 13. But better (well I think so!) we could just reverse channel 6, the aileron master. By changing this one setting we get both ailerons fixed because they are both mixed off that.

So can you begin to see why I like using these master channels? If the problem effects both elements – e.g. left and right ailerons – I can correct both with just one change in the driving master aileron. I like that. Its neat, simple and less prone to me forgetting to change one side! We’ll see a lot more of this in a later post weh we come to fine tune everything.

OK, so it’s all working – but those flaps aren’t half moving quick! Can we slow them down so they look a bit more realistic? Also, I’m not sure that the “flap 1” intermediate position at exactly halfway is right – can we change that? Let’s have a go in the next post.

BEB

[Biggles' Elder Brother - Moderator]

Ailerons and Flap tuning, part one

Now that we have it all going the right way let’s try and get everything aligned and moving in a more scale-like fashion.

We’ll start with the ailerons as they are the easiest. The job is simply getting them aligned with the wing when at neutral and that’s very easy to do as the linkage is out in the open and easily adjusted in length. So that’s exactly what we do – the old fashioned way, no Tx involvement at all!

We can move on to the flaps. We have three jobs to do here:

1. Align the flaps so that they sit flush with the wing and already aligned ailerons when in the ‘up’ position and they are equally deployed on each side at full ‘down’.
2. I want to have two deployed flap positions:
   1. Flaps 1: a take-off setting
   2. Flaps 2: a landing setting

The take-off setting needs to be about 25-30% down, while the landing setting needs to be 100% down. So far; so good. But there is a bit of a problem. I am driving the flaps from the left slider, this has an indent at the centre point of the travel that I can obviously feel when sweeping the slider. Now I’d really like the Flaps 1 setting to be at this mid-point then I could find it repeatedly just by feel. But Flaps 1 is 25% deployment – the indent is at 50%. How do we sort this then? We’ll see.

3. At the moment flaps simply follow the slider – real time. So I can “wiz them” up and down if I want, and if I do wish to have a nice slow scale-like movement I have to do it by slowing moving the slider myself – which ties up my left-hand unnecessarily! Again we need a solution.

OK – so off we go with the first part – aligning the Flaps. As I have said earlier aligning these entirely mechanically would be very difficult because of tricky access to the internal mechanism. So the game is to take each flap as close as possible mechanically and the fine tune it by altering the end point setting of the individual flaps on the outputs tab.

First we do the flaps-up position. These are adjustments of individual flaps (left and right separately) so we do this on the right-flap and left-flap channels of 10 and 14 respectively. Then we examine full flap deployment. Because the starting endpoint (stowed flaps) is different for each flap (despite the fact that they are both in line) the result will be they will deploy to different depths! We need to fix this by adjusting the opposite end point on the other flap so we end up with them aligned when stowed, aligned at any intermediate position and aligned at full deployment. This is a “tweak it, measure it, tweak it again” iterative process until you are satisfied – or run out of patience and decide that near enough is good enough!

You can see how I have done this in the outputs tab below with the two channels’ highlighted showing their altered endpoints.

You might be surpised to see how different the end points are that result in the flaps lining up at all points. Also the diffrence in the range between the endpoints for left and right. Thinking about this I can only really put it down to the fact that the two servos are not a pair. One is a JR retract servo - a RT88, the other is a Spektrum retract servo. Differneces between them would also explain why the legs don't move in unison a fact you can observe in the videos above.

So that’s the first job done with the flaps. In the next post we will move on to items 2 and 3.

BEB

[Biggles' Elder Brother - Moderator]

Flap tuning, part two.

Let’s move on to the second flap issue, getting 50% left slider movement (the central indent) to be only about 25-30% of the flap deployment – so as to form a “flaps-1 take off” setting. We will do this by using a curve.

Open Tx allows us to specify up to 32 different curves. Curves can be applied to pretty well anything, not just throttles! There is an interactive curve editor in Companion that means we can create curves either by clicking and dragging points or by specifying a mathematical equation. When creating a curve using points we can have anything from 2 to 17 points on the curve.

I decided on 11 points and to set the curve up by the click and drag method. For this case it pays to have an odd number of points as then I have a point at the n=mid-range and can set that at the 25-30% level, then I can simply arrange the others around it neatly.

My first go at this looked like this:

You can see how it intersects the centre at about 25% or so and then goes on to full deployment. But when I tested that it was the wrong way round!!! The flaps moved to the ¾ position at the slider halfway indent! Opps!

No problem really, I just moved the points around to get this,….

Again you can see this cuts the centre line at ¼ ( or 3/4 depending in where you count from!)

To actually make the flaps follow the curve and not just remain linear I just have to select input 6 (the left slider) from the inputs screen – see below,….

Then open that up to get the dialogue box for it and set the ‘curve’ value to the number of the curve I created – which was (logically) curve1!. You can see that here,…

OK, so that’s the second job on the flaps done. All that remains is to slow them down a bit – they are a bit quick!

We can do this via the Master Flap dialogue box on the mixes menu. We use the master flap because we want this change to effect both flaps equally – without having to always remember to put it in twice for left and right separately. The picture below shows the dialogue box in question and you can see I have set the “slow” parameter (both up and down) to 4 units. I have no idea what these units are! They seem to be shorter than seconds – you just fiddle with the number until you get the effect you want and the speed you want.

Right then, that’s it for flaps. They are aligned, both in the up and down positions. They have a non-linear setting so they stop at ¼ deployment for half-slider. And they move nice and slow no matter how fast I move the slider.

To finish, here’s a little video showing the flaps operating in all their glory,…

 

The video shows the flaps moving first to the take-off setting and then to full deployment suitable for landing. Note that I am just "flicking" the slider - showing that the Tx is doing the slowing - not me!

Next we will turn our attention to the undercarriage and use our programming to get a bit more realism there as well.

BEB

Edited By Biggles' Elder Brother - Moderator on 13/10/2016 22:10:04

[MattyB]

Posted by Biggles' Elder Brother - Moderator on 12/10/2016 20:11:36:

Getting the control directions right!

Let’s start by fixing the flap on the right wing that is going the wrong way....

...We could fix the problem by simply selecting ‘INV’ in the drop down menu in the Direction box that is arrowed. And that would work, fine. And many people would do that. And there’s nothing wrong with doing that!

But, it isn’t the way I want to do it. I want to do it on the mixer tab – I’m awkward like that!...

....Now the obvious question – why do I like doing this in this rather convoluted complicated way?

If this was simply a straight through control – no mix – that was going the wrong way, then I would servo reverse it on the output tab. Because in my world the ‘fault’ here is with the servo igoing the wrong way – so fix it in the servo output tab. Right?

But that’s not what is happening here. The servo is moving as a result of the mix – it is the mix is that is wrong, not the servo. So it’s the mix we should fix – on the mix tab – not the servo. Geddit?

Now just to be very clear – I am NOT saying “you must do it this way,I am right, all other methods are wrong”. I’m just saying this makes sense to me and it’s how I like to do it. You do it your way!

One of the things you do have to be a bit careful with in OpenTx is the fact that you can change these things at so many different points; at input, at mix, at output etc....

Good post, but a very important point for OpenTX newcomers - there is one "rule" that should be universally followed, and that is do not use negative numbers on the inputs screen for servo reversing. This is because you can end up with reversed trims (i.e. up trim gives down elevator effect and vice versa) on your primary controls which can easily lead to a lost model. It can be a tricky issue to spot (nearly everyone checks the directions of their controls pre-flight, but not normally their trims) and an infuriating one to troubleshoot if you aren't aware of it. Don't be caught out!

Edited By MattyB on 14/10/2016 05:19:43

[Allan Bennett]

Thanks for that one MattyB. As a newcomer, on my first model I've had to reverse only my rudder channel. I can't remember offhand which screen I did it in, but I'll check later and see which way its trim is working.

[Biggles' Elder Brother - Moderator]

Posted by MattyB on 14/10/2016 05:17:31:

Good post, but a very important point for OpenTX newcomers - there is one "rule" that should be universally followed, and that is do not use negative numbers on the inputs screen for servo reversing. This is because you can end up with reversed trims (i.e. up trim gives down elevator effect and vice versa) on your primary controls which can easily lead to a lost model. It can be a tricky issue to spot (nearly everyone checks the directions of their controls pre-flight, but not normally their trims) and an infuriating one to troubleshoot if you aren't aware of it. Don't be caught out!

Edited By MattyB on 14/10/2016 05:19:43

A very goiod point Matty - thanks for higlighting that I'd overlooked it. And this is the sort of dialogue that can help us all.

When you look at how you have done it Allan - just remember that (Matty's caution not withstanding) there is no "right" and "wrong" with this really - there are only ways you want to do it that make sense to you!

Having said that it is propably wise to be consistent with yourself at least - ie, if for a certain circumestance you reverse it on the output tab than stick with that. Don't sometimes solve that problem one way and other times another way - that is a recipe of confusion!

BEB

PS Anyone else feeling ready to take the plunge? I'm sure there are loads of inetresting little bits of OpenTx programming out there we copuld all learn something from. Come on guys, don't be shy, share it we us - just start a thread in this section. Could be a big project, could be just a little rouse you're pleased with that got something working. Doesn' matter, tney are all interesting.

[Bob Cotsford]

BEB, you have probably covered it already but are you using one output for the retracts or on one for each leg? I like to use one for each leg so that I can put a delay on one output - warbirds usually had one leg start to retract before the other to reduce the load on the hydraulics. See my FW 152 thread for an example.

[Biggles' Elder Brother - Moderator]

Bob - that is exactly what I am doing next! Watch this space!

BEB

[Biggles' Elder Brother - Moderator]

Sorting the U/C

Let’s have a look at the gear now. We’ve got it working OK, but it does tend to “snap” up and down a bit! Also, as Bob says, WWII warbirds U/C rarely went up (or down) together! One always seems to lag behind. So it would be nice (just for a bit a scale effect and because we can!) to mimick all this. So what I would like to do is:

1. Slow the movement of the gear down to more realistic level. To be really smart it would be great if it went down slightly faster than it goes up! This happened on the full0size because of course when lowering the gear the system has gravity to help it and so it goes faster!
2. Let’s try and arrange it so that the legs go up in a staggered fashion – one leading the other.

So, starting with the speed. As I said I’d really like to do this – unfortunately I can’t! This is an example of where the Tx can achieve things the hardware can’t do. You see retract servos have no proportionality potentiometer in them, all they do is the instant the input crosses some threshold they just switch, at full speed, end to end. Bang, bang, no intermediate positions. So, OpenTx can do it – but it won’t do anything on the retracts themselves – sorry, we are stuck with “snapping up and down”. I’m not certain, but I think electric retracts can be slowed? Has anyone tried that?

Let’s move swiftly on to something we can do, staggering the leg movement. You can see from the picture in a previous post dealing with slowing dflap movement that next to the slowing boxes (just to their immediate left) there are boxes marked “delay”. That’s handy! Basically, put a value in there and the action that has been initiated – in this case lowering, or raising, the gear won’t be commenced until after a delay period. Sounds just like what we want!

The picture below shows the final arrangement I came up with. We only need to delay one leg (over the other) so we can work with the left or the right as we choose – I have chosen the right, a purely arbitary choice.

And that’s all there is to it. You stick in a value in, give it go. If you don’t like it, change the value, try again and so on until you are happy. I found that 0.8 worked for me.

To finish this bit off here is a video of my legs staggering around!

Less than ideal – but the best I think we can do.

Well, we are nearly finished with this wing. In the final two parts I’ll just explain how I have added voice alerts on flaps (that tells me what position the flaps are in) and the U/C (that tells me if the gear is up or down) and revisit the failsafe showing how that can be set up in a complex environment like this.

BEB

[Biggles' Elder Brother - Moderator]

Adding Voices.

When transmitters learnt to talk a few years ago I must admit I was rather spectical. “Why would I want a talking transmitter – I get enough of that from Mrs BEB” (it’s a good job she doesn’t read this stuff!)

But since then I have become a convert and now I program a voice message with all of my switches. Frank I think it was above who talked about the risk of hitting the wrong switch – well that can happen of course but I would know it because I wouldn’t get the verbal conformation I was expecting.

Setting up voice messages in OpenTx is very easy. It comes under the area of the “Special Functions” tab in Companion. You can see my set up so far for this model in the picture below,…

The way this works is pretty intuitive. The first column gives us the special function number (SF1, SF2,..etc.) The second column tells us what switch setting will make that function happen. For example if you go down to SF5 you will see that this function will be acted out if switch SA is in the ‘up’ position. SF6 will be executed if switch SA is in the middle position, while SF7 will happen if SA is ‘down’. Column 3 tell us what exactly will happen; looking at SF5 again we see that what will happen is that a sound track will be played. Column 4 contains the name of the ‘wav’ file on the transmitters SD card that will be played – in the case of SF5 that will be the file ‘Ele-hi.wav’. This file is a recording of a syntheisied woman's voice saying the phrase “Elevator High Rates”. The final column tells OpenTx that it is to play this file just once when the switch is first put in that position. Under other options you can have the function automatically repeat at intervals for example.

What if the phrase you want isn’t on the SD card? No problem, there are any number of free software widgets on the internet that will convert a typed-in expression to a synthesised voice sample captured in a ‘wav’ file! You could even record yourself saying it – or your wife,…on second thoughts,….Once you have the recording you just upload it to the SOUNDS/en directory on the transmitter's SD card and its there for you to use - dead easy.

Now the more observant among you might notice that some of the activitation switches in the photo above have names like L4 and L6 etc. These are wonderful devices called "logical switches" and you can do all sorts of things with them! I'll explain a bit more about them and how I'm using them here in the next post.

BEB

Edited By Biggles' Elder Brother - Moderator on 14/10/2016 16:44:58

[Martin McIntosh]

Regarding the retract speed, you obviously need to use normal servos, not retract ones. On my 44" Spit I used some small metal geared ones. The 62" one uses MG995 rubbish which are still working very well after many years. I fitted resistors (about 1K0) to each end of the pot. track to give 180 deg. travel. You must of course use mechanical units to do this. The servo slow feature can then be used to give the effect of one retracting before the other. Wish that I knew a way to do this with electric or air ones. Restricting the air supply just means less power and they don`t work.

I envy those guys with the giant scale models who have got this problem sorted since I hate the u/c whipping up in an instant on some of my other models.

[MattyB]

Posted by Biggles' Elder Brother - Moderator on 14/10/2016 11:50:56:

PS Anyone else feeling ready to take the plunge? I'm sure there are loads of inetresting little bits of OpenTx programming out there we copuld all learn something from. Come on guys, don't be shy, share it we us - just start a thread in this section. Could be a big project, could be just a little rouse you're pleased with that got something working. Doesn' matter, tney are all interesting.

I am at the airport travelling back from the US at present, but when I get the chance I will do a mini tutorial on logical switches and how they can be linked together in "cascades" to deliver incredible functionality. They are my favourite bit of OpenTX by far.

Edited By MattyB on 14/10/2016 20:34:48

[Bob Cotsford]

Ref electric retracts - the short answer is no, you can't influence the retract speed as they too rely on a 1.5 millisecond switching point rather than following the pulse length. I think there are brands that can be programmed for slow speed, possibly Lado, but I find their retraction speed out of the box about right.

[MattyB]

I can't understand why more manufacturers don't offer electric retracts with slowing - I know it is a worm gear mechanism, but surely it must be possible? Based on the price of the EFlite units they certainly have enough margin to add this feature without raising costs too much...

[Biggles' Elder Brother - Moderator]

Posted by MattyB on 14/10/2016 20:31:22:

Posted by Biggles' Elder Brother - Moderator on 14/10/2016 11:50:56:

PS Anyone else feeling ready to take the plunge? I'm sure there are loads of inetresting little bits of OpenTx programming out there we copuld all learn something from. Come on guys, don't be shy, share it we us - just start a thread in this section. Could be a big project, could be just a little rouse you're pleased with that got something working. Doesn' matter, tney are all interesting.

I am at the airport travelling back from the US at present, but when I get the chance I will do a mini tutorial on logical switches and how they can be linked together in "cascades" to deliver incredible functionality. They are my favourite bit of OpenTX by far.

Edited By MattyB on 14/10/2016 20:34:48

Oh very good. I, and I'm sure many others, would be very interested. Logical switches are a powerful tool!. I'll just show some very simple things I've done on this project soon and that might act as an intro for the more advanced stuff! Excellent. Looking forward to that!

BEB

[Biggles' Elder Brother - Moderator]

Logical Switches

As promised I’ll say a little bit about logical switches. Matty will probably go into a lot more depth with these, but I just give you a flavour and an introduction that might beuseful if you haven’t used them before or haven’t done much with them.

OK, so what is a logical switch? Well it’s a virtual switch, that is it only exists in the software inside the Tx, it isn’t a physical switch on the outside of the Tx. But, just like a physical switch it can be ‘on’ or ‘off’. Which of these it is depends upon some ‘logical condition’. For example consider the statement

CH4>75

This is a logical statement and it is true if the current value of channel 4 is greater than 75. Remember a channel can go from -100 (full deflection one way) to +100 (full deflection the other way).

If we were to link a logical switch to this statement then the switch is ‘on’ if the statement is true and ‘off’ if the statement is not true. So that means we can turn a switch on and off automatically depending on the value of CH4. The really clever thing is you can daisy chain these things together with conditions like “if A AND B OR C then do this” were A, B and C are conditions like the CH4>75 above

An example would help here I think, you could arrange it so that “if the gear was down AND the flaps were fully deployed then turn the landing light on automatically”.

My use of logical switches here is a bit unusual – and very simple! I wanted OpenTx to announce “Flaps Up”, “Flaps 1” and “Flaps 2”. So I arranged it so that one of these 3 announcements would be triggered if one of logical switches L4, L5 and L6 respectively were turned on. You can see this set up in the photo below:

Next I have to define the logical switches themselves. Logically enough (!) this is done on the Logical Switches tab which is shown below,…

Let’s look at L4 first. The “function” column is set at ‘a>x’ – that means that if variable in te column V1 is greater than variable in the column V2, then the switch will be ‘on’. The next two columns define variables V1 and V2. V1 is the value of the left slider (which is our flap control) and variable V2 is the constant 90. So that basically says, “if LS is more than 90 turn the logical switch L4 on”. If L4 is ‘on’ then the special function SF11, see the first image above, will play the track “flapsup”. Great – just what we want.

So why ‘if LS is greater than 90’? Why not say ‘If LS equals 100”? Surely that is truly “flaps up”? Well in programming generally it is not a good idea to test for a specific value – you see a specific value is just that – one unique number. You might never actually see it – LS might never be exactly 100.

We don’t need fantastic precision here – “greater than 90” is 95% up – on a +-100 scale – that’s near enough to be worth telling me the flaps are up!

Full flap deployment on logical switch L6 works the same way – only this time we test to see “if LS is less than -90” (note -91 is less than -90!) So that is the same as L4 just at the other end of the scale.

Take a look at L5 – that is a bit different. I’ve had to box a bit clever here. What I want to do is to trigger a verbal confirmation saying “Flaps1” (which is SF 10 in the top image above) when the left slider LS is at the midpoint. So could I write “if LS equals 0 then L5 is on”. Well, the problem is as above - what if there is just a bit of mid-point drift? What of the calibration is just a bit out? Any of those might result in the central indent giving us -1, or 1, instead of 0. Result the slider is in the middle but L5 isn’t ‘on’ because LS isn’t exactly 0. And I won’t be able to “fiddle” this because “LS=0” is a tiny, tiny point on the LS scale! The same could happen simply because my sausage-like fingers get the slider very close to the central indent but not quite there and on a cold day I don’t notice!

So how do I get round this? Answer I use a concept called “the absolute value”. You can see that the function in L5 is not a<x instead its |a|<x. This basically means ignore the sign of ‘a’; if ‘a’ is negative just make it positive, then test it against the constant 10. Let’s look at how this works:

If a=8, well that’s less than 10 so the switch goes on.

If a=-8, then turn it to 8, then test, its less than 10 so the switch goes on.

The effect of this is that the switch will go on for any value of LS from -9 to +9 – in other words anywhere approximately about the centre!! Just what we want! As long as I am more or less in the middle, within 10%, the Tx will play the sound file “Flaps1”.

These are rather non-typical applications of logical switches, and in truth very simple ones. But I think that the latter point at least makes them good introductory material if you haven’t come across this concept before.

Next we’ll finish off by sorting the failsafe out properly for this wing.

BEB

[Biggles' Elder Brother - Moderator]

Sorting the Failsafe.

Right, well here’s the last part. Tidied up the cables – the decoders are now inside the wing and all that protrudes is the two SBUS inputs. These will be connected to a Y-lead attached as a flying lead from the SBUS connector of the X8R receiver. So, yes, OK two cables to connect but it means the wing can still be taken into two parts for transport and/or storage. Of course it doesn’t matter which leg of the Y-lead you attach to which lead – both carry the full 16 channels so it makes no difference and I can’t get it wrong!

Here is a photo of the final arrangement – quite neat think!

You might be wondering about those wooden discs? I have loads of these in the scrap box. Basically I take one of these discs, cut a slot to the centre. Then I place the servo wire in the slot. Finally I fill the outer half of the slot with epoxy. Why? It stops the wire falling back inside the wing – but at the same time it’s very easy to remove if I want to. Simps!

Now, on to the thorny question of failsafes! There are two problems with failsafes in this context.

The first is that whatever failsafe combination we come up with it is always possible to envisage a scenario in which that would be absolutely the worse thing to do! So what have I decided to have? I want the following:

• Primary flying controls (rudder, elevator and ailerons) to neutral.
• Motor throttled right back.
• Flaps up
• Gear up

The idea of ensuring the flaps and undercarriage are up is simple “damage limitation”! The rest is an attempt to bring it down “straight ahead” – well more or less!

The second problem is that, with all these multi-layered mixes, we can’t be exactly sure what is going to happen when it goes into failsafe! The only way to know for sure is to try it! Now a note of caution here – I’m sure I don’t have to say this but “for the record” – if you are going to have the motor powered doing this - take the prop off! I’m only doing the wing at this stage – so it’s not an issue for me here.

So, how to test it? Easy, fire it up, check the radio link is good, green light on the Rx etc. wiggle the controls. Then,….turn off the Tx and wait to see what happens! After a couple of seconds the Rx will go into failsafe. Then note where everything ends up.

On my first attempt at this I ended up with one flap fully down, one fully up and one leg down! Had I not checked, and that had happened in the air, it would have been a disaster and potentially dangerous. The one deployed flap would have probably pulled the aircraft into a skewed roll traveling sideways – possibly towards me! But of course that is why we check – so that doesn’t happen.

I made some changes to the failsafe spec on the “set up” tab – as shown below,….

You can see how the correct failsafe requires a combination of plus and minus settings - with right wing values tending to be negative and left wing values positive! We can now test that this works. The first test is starting from the “in normal flight” situation of gear and flaps already both up. When the Rx goes into failsafe in this case nothing should happen – everything should stay where it is with the ailerons neutral, the gear up and flaps up. Here is video of that test,…listen carefully to hear when I turn the Tx off,...

That wasn’t very exciting was it? About a good as watching paint dry! But of course that’s because the wing did exactly what we expected – nothing!

The next test is the opposite one – the landing condition – and should be a bit more interesting; gear down and flaps at full deployment (flap 2 position). In this case, when the Rx goes into failsafe, the gear should go up and the flaps stow to the flaps-up position with the ailerons at neutral. And here is a video of the test,…

Again all goes well with everything acting as it should; the gear and the flaps go up and the ailerons are at neutral. Great!

I can’t stress how important it is to do these failsafe tests – remember we have a responsibility to do this!

I will not stop failsafe testing here – this is just an intermediate test for the wing. I will test the fuselage (rudder, elevator and throttle) when they are ready and then I will test the whole system before the maiden flight.

Well, I think that’s it – job done. I hope you have found it useful and if it encourages few others to share their OpenTx exploits that would be great. Remember it doesn’t have to be anything very fancy – it could just be a small thing – they are all of interest. So please think about joining in.

BEB

[Allan Bennett]

Thanks for those "tutorials" BEB, especially the one on logical switches.

I had looked at that screen several times but hadn't got around to reading about it in the manual. It would have helped me understand it more quickly if the V1 and V2 columns in the screen were labelled "a" and "x" instead, for that's the terms used by the equations in the left column. But your post has sorted it for me.

[Kamikazi]

Hi BEB

Could you possibly explain the multiplex functions "ADD" "MULTIPLY" and "REPLACE"

I try not to live up to my handle.

Tony

[Biggles' Elder Brother - Moderator]

Hi Kam - sorry about the delay in replying - I've been out all day. Went to Elvington, to the museum there - excellent. I can highly recommend it.

Anyway - to the point. These options appear in the mixer tab. Basically they describe how the input you are refering to will be incorporated into the channel in question.

Will the value be "Added" to the channel? This is the case in a classic mix where you want to "add" say some rudder when the ailerons are used. So you "add" 10% of the aileron movement onto what ever the rudder is already at. This is probably the most common case.

Will it "replace" whatever value is currently on the channel - effectively "overwriting" it? The value the channel is getting from elsewhere is not added to, it is overwritten and thus lost. This is useful in 'absolute' cases where something is either one thing or another - but not intermediary; such as when you are controlling the undercarraiage - its either up or its down - it can't be half way. An LED is either on or its off. You might "replace" the value in these cases. Note - you don't have to - but it is one way of doing it.

You can also multiply the channel by the input - if anyone finds a use for that can you tell me! I'm sure its dead useful - I've just never conceived of a use yet!

Hope that helps.

BEB

Edited By Biggles' Elder Brother - Moderator on 17/10/2016 23:39:52