The whys and wherefores of programming

[Pete B]

OK, so it's time to come clean - a very significant part of the programming of my DX8 is done in complete and utter ignorance.....

Try as i might, I've yet to find anything, anywhere on the web which explains, in words of one syllable, what certain functions do, why we need to do it and how we achieve the end result.

I even bought a book on the DX8 and, whilst helping to an extent, the essential whys and wherefores were completely absent, so it's back to following simple instructions again.

I've recently installed the sailplane programming and, with some patient help from Chris Bott, I've eventually got the idea of flight modes clear in my head.

However, I have a complete mental block when I encounter switch allocations, rates, offsets and mixes. Setting a switch to operate an electronic switch was achieved with a bit of help and a lot of luck - but with no comprehension whatsoever.....

Every thread or web page i read, and I promise you it runs into dozens, makes huge assumptions about the level of understanding of the reader and I would dearly love to be able to understand why and how I achieve a particular aim, rather than just follow instructions parrot-fashion.

So, as an opener, can anyone provide, or point me towards, easily-understandable explanations for the following, please?:

What does a mix do?

How do we decide what to mix with what?

Why do you mix a function with itself?

What effect does that have?

How do you set a switch to operate a mix?

What are 'rates' and 'offsets'?

When do we need to adjust the rate and offset - and what does it do?

Phew, I've probably not exhausted the questions but think that'll do for now - you get the idea.....

I'll only ask that, if any one can gird his loins enough to respond, he uses the aforesaid single syllable words and works on the premise that I am a numpty. I fully expect that my first reply will be "Sorry, not simple enough..."

Pete

ps ...and I bet I'm not the only one who'd like to know!

[Chris Bott - Moderator]

Hi Pete, thanks for the kind mention.

I'll have a go at putting what I think about mixes into words, let's see where this goes.
Excluding pre set mixes.

Consider the value of a standard channel as a number between -100 and +100, with 0 as the centre point.

When we do a mix, we pass this number on to the slave channel.
If we want the slave channel to move in exactly the same way as the master (when we move the master stick), then we pass this number on at 100%. (multiplied by 1).

The DX8 gives us the option of changing this multiplier (they call it rates), so that say 100% of throttle movement, gives us 10% of elevator movement as compensation (we might do this instead of adjusting downthrust).
The DX8 also gives us the option of using a different multiplier either side of zero, maybe with an elevator to aileron mix we might want the effect from up elevator to be more than that from down. So they give us two multipliers to use.

So a mix makes the action followed by one channel, also affect another.

We might need an offset, because the master channel may normally sit at something other than zero, so when we add this to another channel, the slave channel gets moved a little, using an offset is a way of putting it back where we want it. This is particularly necessary when we assign a switch to switch a mix on and off. The last thing we want, is that switch causing the slave channel neutral to move.

Don't forget though, that this is complicated by the fact that the slave channel may or may not already be controlled by it's own switch or stick, when a mix from another channel is applied, you end up with the combined effect of both inputs.

[SkippyUK]

Speaking strictly from personal experience, Mixing and switch to operate mix.

I've experimented with mixing ailerons with rudder on my SE5a to give it a more scale turn - saw it on a forum and gave it a try.

Essentially I mix a small bit of rudder input (that is the left or right stick movement) into the opposite aileron channel so that when I turn right, the ailerons automatically do a slight roll left to avoid it dropping it's right wing too much.

I normally do this manually but gave it a go.

I used MIX1 to activate this mix so that with it off, plane worked as normal and with MIX1 on, it mixed rudder into ailerons.

Hope this is what you wanted to discuss - if not, just ignore my ramblings .

Skippy

[kevin b]

No good asking me. I've only just mastered how to work my microwave oven ! I do keep looking at the instruction manual for my Futaba T6EXP, but then I sigh and put it down. No chance with a top spec tranny. It was a lot easier when we used to just plug everything in and twiddle the sticks.

kevinb.

[Foxfan]

Pete, you certainly aren't the only one!

And I don't even have a computer TX! But it does have switches and rates.

I'd love to read a definitive treatise for complete programming numpties too.

Martin

[SkippyUK]

There was a famous Programming manual for the Futaba FF7 which I have somewhere but the manuals for the old 7C is quite good at trying to explain 'why' you might need the function compared to the DX8 which seems to just guide you to the place where you adjust it.

It's here

Must be that back in the older days the authors didn't expect you to know everything before reading the manual.

Skippy

[Frank Skilbeck]

Offset is often used on gliders to center the flap so you only get a little up and down on the flap switch/lever, reflex for speed and camber for thermal, still leaving substansially more down for crow breaking which is usually a mix with the spoilers, add a little elevator compensation in to stop the glider from zooming up when you deploy the spoilers and you can start to see where these are useful.

Although the programming approach is different the Multiplex Tx manuals and the Tutorial, which you can down load, not only gives a good overview of the various mixs but also what they do.

[Pete B]

Thanks for the replies, gents, but, as expected, it's not easy to bring this down to a straightforward, step-by-step explanation, so sadly I'm none the wiser.

I've downloaded the FF7 manual and I like the idea of the 'goal, steps and inputs' layout of the tutorial. Equally, the EVO tutorial goes to considerable lengths to explain the whys and wherefores, and I can see I've got a bit of reading ahead of me.

Unfortunately, of course, neither is of real practical use for a Spektrum Tx and ideally, I'd try not to confuse myself further by involving unrelated systems but, until someone writes a Spektrum-based Guide for Dummies, it might be the best I can get.

Frank, I understand what each control setting does and why we need to set the controls as we do - it's the construction and application of mixes that is pretty impenetrable. For instance, I have a Radian Pro aero program on my DX8. What is the logic chain which produces the 4 mixes to allow crow and camber?: Mix 1 is FLP>LAL: Mix2 is AX2>LAL; Mix 3 is AX2>FLP; 4 is AX2>AX2, all with various rates and offsets. I cannot begin to see how that is formed.

Coupled aileron and rudder is no problem ,BEB- I've set it on many of my models, as well as other simple mixes. The difference is, of course, that in the DX8 you simply select the pre-set mix AIL>RUD and dial in a percentage - job done. It's when you get to the free mixes with two rate values and an offset value, with a trim option and switch selection, that the brain grinds to a halt....

I'm beginning to think the answer would be a blackboard, chalk and a very patient teacher....might be old-fashioned but would probably be the best way to learn!

Pete

[Biggles' Elder Brother - Moderator]

OK - I've removed my post because I've misunderstood what you were asking! I thought you literally meant a basic expliantion of mixing!!

BEB

[Biggles' Elder Brother - Moderator]

Are all the mixes you describe above active at the same time Pete? If mixes 1 & 2 were active on their own I could understand that - wouldn't that just mean "Flap follows left aileron, right aileron follows left aileron" - a classic camber set?

BEB

Edited By Biggles' Elder Brother - Moderator on 30/08/2013 00:45:31

[Tim A]

Three cheers for you Pete, I thought I was the only one and to embarrassed to say so. Both manuals I have (DX6i & Hitec Aurora 9) seem to take it for granted that you know what & why - try setting up flaps using ailerons on the DX6i I could get one or the other but not both. After several nights I figured out you have to do it in a certain order ie flaps then ailerons, no mention of that in the book - ARRRGH. As for Aurora it says you can set up several flight modes this way but one mode may affect another - how ? why? when? -ARRRGH Again.

As for offset according to Wikipedia one meaning is Offset (geometry), the shape driven out from an original shape in equal distance and direction, normally or perpendicularly to the original shape.

Oh that really clears that up - NOT.

Someone with more brains than me not too many mind KISS applies here, should/could write a series in RCME covering this call it Computer Flying for Dummies.

Kiwikanfli mixed up & offset

[Foxfan]

You guys are talking DX6is and Aurora 9s. How about the Jeti DC16?? I watched the programming youtube and actually, it was pretty easy, but as Pete says, it still doesn't explain WHY you need these actions and what they DO.

Yes, I'd kill for a Jeti, but would I use it all? I'll never have a fancy glider, nowhere to use one and they seem to be where all these channels disappear to.

Assignment of channels and switches? How about that one?

Accellerometers?? Aaarghh! Tip it sideways and a sexy cougar tells you the time?? This all getting weird. I just want to steer me aeroplane please!

Martin

[Essjay]

Hi Pete, I hope you and the other mods don't mind me posting a link to another forum which has some great info on the DX8 Sailplane programming. It's on RCGroups, and there is a wealth of info on the subject. Also at post #426 there are a couple of downloads by Sherman Knight the Team Horizon Hobby Sailplane expert. One is an excellent DX8 guide in PDF form, and also a sailplane SPM file for the DX8 for the Radian Pro.

**LINK**

Edited By Essjay on 30/08/2013 12:33:30

[Chris Bott - Moderator]

Posted by Pete B - Moderator on 30/08/2013 00:34:54:

For instance, I have a Radian Pro aero program on my DX8. What is the logic chain which produces the 4 mixes to allow crow and camber?: Mix 1 is FLP>LAL: Mix2 is AX2>LAL; Mix 3 is AX2>FLP; 4 is AX2>AX2, all with various rates and offsets. I cannot begin to see how that is formed.

Pete

 

Starting with 4. AX2>AX2 is likely to be at a rate of -100%? If so, this adds minus amounts of the Aux 2 switch, to Aux 2. This is used to stop the AX2 switch adjusting the AX2 output.

Number 3. AX2>FLP Makes the FLP servo output move when the AX2 Switch is operated. How much it moves is governed by the rate figures.

Number 2. AX2>LAL Makes the Aileron servos ** move when the AX2 switch is operated, again by the amount governed by the rate.

Number 1. Flap>LAL Also makes the Aileron servos ** move, when the flap Switch is operated. This mix may well be switched on/off by another switch?

** The reason that only LAL is chosen when we want to make both ailerons move, is due to Spectrums peculiar, confusing but very useful feature that I think is called back mixing. In this case, we mix to LAL and the spectrum system makes this move both ailerons in the same direction. If we want both ailerons to move in opposite directions, we'd mix to RAL instead. This feature saves us using two mixes for this type of function (which would otherwise need a mix to LAL and a mix to RAL).

Edited By Chris Bott - Moderator on 30/08/2013 17:16:24

[Frank Skilbeck]

Posted by Pete B - Moderator on 30/08/2013 00:34:54:

Frank, I understand what each control setting does and why we need to set the controls as we do - it's the construction and application of mixes that is pretty impenetrable. For instance, I have a Radian Pro aero program on my DX8. What is the logic chain which produces the 4 mixes to allow crow and camber?: Mix 1 is FLP>LAL: Mix2 is AX2>LAL; Mix 3 is AX2>FLP; 4 is AX2>AX2, all with various rates and offsets. I cannot begin to see how that is formed.

Pete

While I have a Dx6i for my BnF stuff I use a MPX Cockpit Sx and Royal Pro for my gliders and I can see why that seems a bit complicated, but even these use the same number of mixes just presented in a different way, but you should have seen the dial, trim and slider fiddling I used to have to do when dialing in crow on my HP18 glider using my old Fleet PCM 7 set, programming might take some understanding but once set up it can make the flying a little less complicated.

[andyh]

I'm watching this thread with interest. I recently bought a p2k (which narrowly edged it over a radian pro) & a dx7s to do the funky mixing

I've only been back in the hobby a few months, after a loooong layoff, but would I be right in thinking that models such as these have brought 'full-house' glider mixing to the mainstream relatively recently?

call me crazy, but if there were a specialist-interest publication (no, not that type) who was looking for article ideas, this might be a good suggestion? does anyone know of such an organ (no, not that type)?

[Peter Jenkins]

What I find best is to think about what I want the aeroplane to do or not do. For example, a Wot4 has very strong secondary effect of rudder i.e. left rudder leads to an almost instant left roll. If you want to do a slow roll and use the rudder as well as elevator to get a nice axial roll, you need to kill the secondary effect of rudder. To put it another way, if you apply rudder you just want a yaw and not a roll. Say you apply left rudder and the aircraft rolls left then you want your ailerons to compensate by rolling right so that the rudder induced roll is neurtralised and you just get yaw. Does that make sense?

Well, first rule of mixing is to make the mix value high so that you can see if your mix is going in the right direction. For the rudder to aileron mix you only need a very small amout of mixing - usually less than 5% so it's important you set it the right way - how do I know? The second rule of mixing is to use a switch to bring it in and to try it out at a safe height!

I find that helps with when I'm trying to put a mix in place. If this helps fine, if not just ignore this.

[andyh]

Posted by Peter Jenkins on 30/08/2013 23:45:20:

What I find best is to think about what I want the aeroplane to do or not do. For example, a Wot4 has very strong secondary effect of rudder i.e. left rudder leads to an almost instant left roll. If you want to do a slow roll and use the rudder as well as elevator to get a nice axial roll, you need to kill the secondary effect of rudder. To put it another way, if you apply rudder you just want a yaw and not a roll. Say you apply left rudder and the aircraft rolls left then you want your ailerons to compensate by rolling right so that the rudder induced roll is neurtralised and you just get yaw. Does that make sense?

eugh

left roll on left rudder on a wot4; who'd've guessed?

[Pete B]

No problem with that link, Essjay - I've been subscribed to that thread myself and it has been useful but life is too short to follow it word-for-word. However, I must have overlooked that PDF which does look rather useful - I shall read it at my leisure. Thanks for that

I'll reiterate for those explaining what a mix is - I know what they do and I regularly use them! My point was that I cannot fathom out how to initiate a mix for myself and create a set of instructions to achieve a certain result.....

BUT! - light is dawning, thanks to Chris Bott's post just above, which is the simplest and most useful paragraph I've found anywhere so far. Having read it through several times, I'm beginning to understand that the rates for a particular function, ie AX2>AX2 aren't just a process deep inside the electronics but actually serve to adjust the response of the switch on the Tx, which is a significant breakthrough for me!

I'm not home and dry yet, I'm sure, but it's given me a good basis on which to spend some time fiddling with the Tx

With a bit of luck, this thread might help to clear the fog I'm sure more than a few forumites find themselves in.

Ta, Chris - have you thought about writing a book?....

Pete

[Tim Mackey]

Im not gonna repeat the good stuff already done, but may just mention the difference ( in simplistic terms cos thats what I think is beiong asked for ) the difference between "Fixed", and "Free" mixes.

"Fixed" mixes are already setup in the tx as standard and would include such things as elevon, or perhaps coupled aileron rudder etc. These are popular mixes, so most manufacturers include them, although there usually is the facility to alter the rate of mix etc. Expect to find at least a couple of fixed mixes in most mid range sets.

"Free" mixes are ones that the user is "free" to concoct himself - perhaps things like mixing gear with flaps or similar... allowing a single switch operation to deploy flaps, yet also automatically drop the gear and so on.

In that case, the "master" channnel would be flaps, and the "slave" channel would be gear.

If one wanted to activate flaps as the gear was dropped, then gear would be the mastger, and flaps the slave.

The number of free mixes available varfies from set to set, but around 6 minimum would be normal. There amy also, in some sets, be a few restrictions as to what can be mixed - such as some wont allow a throttle channel to be a slave and so on.

Finally, remember that if your set ( DX8 certainly has ) has a monitor screen, then often the easiest way to see the effect of a mix is to watch that screen