Solving the DX8 spectrum mix setting mystery.

[ArchmageAU]

Ever wondered what the numbers in mix setting mean on the DX8 in heli models?

You have:

• Master channel
• Slave channel
• Rate: <high percentage> <low percentage>
• Offset: <percentage>
• Trim: <INH/ACT>
• Flight Mode: N12HM

To most except the Spectrum Inner sanctum, these have remained a source of trial and error.

The text from the manual is:

Adjusting Programmable Mix Rates
Rotate the roller to highlight the desired rate then press. Rotate the roller to adjust the value. You can reverse the direction of the slave channel with positive and negative values. Adjust the rate for both directions/values.

You should verify that the programmable mix is working properly and in the correct direction. Place the flight mode switch in one of the active positions. Move the programmed master channel while observing the slave channel. The slave channel should move accordingly.

Offset

The Offset function establishes the point at which the two mix rates converge. Typically, this rate is center or 0%. If an offset is needed (normally not in a helicopter), do the following.

The above offers almost no explanation of how the numbers really work.

What is really going on.

I'll ignore the trim, but expose the rest.

The master channel is the control channel. It's current absolute value (from -150 to +150) is what is important here.

The slave channel is the control channel being altered. It plays only a "carrier" role of the output value from the mix. The mix value derived from the master channel is simply added to the output value on the slave channel.

The Flight modes are fairly self explanatory except for M. M (Mix) is the Gear switch in HELI mode. The great thing about this is now you have a 2 position switch that can be used to enable and disable a mix for ALL flight modes. Gear 1 is mix enabled, Gear 0 is mix disabled. Be careful when using this as it ALWAYS applies regardless of the flight mode. (ie. if you use this for throttle manipulation, it will also manipulate when throttle hold is on).

Now to mix numbers.

Think of the high rate percentage and the low rate percentage as the value the mix will have if the master channel is at +100 and -100 respectively. When the master channel is 0, it will have a value of 0 (irrespective of these other rate numbers). The adjust value of the mix changes linearly as the mix channel moves from centre to (OR PAST) either of these end points.

Offset is where it becomes tricky. Offset is how far to move this entire range so 0 has no change. This is where most peoples brains explode or implode.

If we have an offset of 50, The master channel must be at 50 for no change to slave channel. With this same offset of 50, if the master channel is at -50, the low rate is applied. With this same offset of 50, if the master channel is at -100, 1.5 times the low rate will be applied. With this same offset of 50, if the master channel is at +100, 0.5 times the high rate will be applied to the slave channel.

Last point is that mixes are applied cumulatively. If you have two mixes that affect the same slave channel, both output changes will be applied. That changes will be applied in the order of the Mix configuration. ie. Mix 1 is evaluated first, then Mix 2 (and so on). One other note on this is that all mixes occur to channel outputs and are not available as master inputs for other mixes. ie. If Mix 1 changes Aux2 output, and Mix 2 uses Aux2 to change Throttle, the alterations to the Aux2 output will not be used for the Mix 2 input (as it uses the source Aux2 value).


Uses and abuses for Mixing

My main abuse for mixing is to get more idle up modes (6) for my 130x. Next is to allow rescue on my X5 through the BD3SX.


6 Idle up modes

To get the 6 idle up modes (100, 95, 90, 85, 80 and 75% flat throttle) I use the following 2 mixes.

Mix 1 - Ax2 > Thr 0% -10% 100% (f.mode 2)
Mix 2 - Ax2 > Thr -10% 0% -100% (f.mode 1)

My throttle channel is flat 85% for UI1 and 100% for UI2 . Aux2 is controlled by the Gov switch.

What this does.

When Gov is in pos 0, it output Aux2 +100. Gov pos 1 = Aux2 0. Gov pos 2 = Aux2 -100.

• In f.mode 2 and gov 0 (top), throttle is 100% (Mix 1 - 100% offset, so master channel at 100 means 0 change).
• In f.mode 2 and gov 1 (middle), throttle is 95% (Mix 1 - 100% offset. At master value of 0, -10 is applied as master channel is -100 compared to offset (-10 = -5% in throttle terms)).
• In f.mode 2 and gov 2 (bottom), throttle is 90% (Mix 1 - 100% offset, At master value of -100, -20 is applied as master channel is -200 compared to offset (-20 = 2*-10 as master channel is 2 times further than endpoint from offset). (-20 = -10% throttle terms)).
• In f.mode 1 and gov 2 (bottom), throttle is 85% (Mix 2 - -100% offset, so master channel at -100 means 0 change, Throttle curve is 85% of UI1).
• In f.mode 1 and gov 1 (middle), throttle is 80% (Mix 2 - -100% offset. At master value of 0, -10 is applied as master channel is +100 compared to offset (-10 = -5% in throttle terms)).
• In f.mode 2 and gov 0 (top), throttle is 75% (Mix 2 - -100% offset, At master value of 100, -20 is applied as master channel is +200 compared to offset (-20 = 2*-10 as master channel is 2 times further than endpoint from offset). (-20 = -10% throttle terms)).

BD3SX rescue with auto level

My X5 mixes are for rescue facility on the BD3SX and mix Aux3 to pull the Aux2 channel to full negative when the Aux3 goes to -100 (Aux3 is assigned to my bind button, Aux2 channel is the BD3SX SL channel and assigned to the Gov switch).

To pull the Aux2 channel to full negative when the Aux3 goes to -100 I use the following single mix.

Mix 6 - Ax3 > Ax2 0% -125% 100% (f.mode N12H)

As the Aux 3 channel moves from +100 (no change) to -100, its change relative to the offset is -200 (200%), so -250 (or 2*-125) is applied to the Aux2 channel. This single mix ensures that no matter what the value of the self level (I have only up to 45%), it will pull it to full negative.

The last bit of magic, is during this rescue, I also want to centre the cyclics (elevator and aileron). I was told this cannot be done (which is why the investigation into mixing). I found a way.

Mix 1 - Ax3 > Ail 0% -125% 100% (f.mode N12H)
Mix 2 - Ax3 > Ail 0% 75% 100% (f.mode N12H)
Mix 3 - Ax3 > Ele 0% -125% 100% (f.mode N12H)
Mix 4 - Ax3 > Ele 0% 75% 100% (f.mode N12H)

Like the previous Aux2 channel, I pull the channel, hard to it's bottom limit (wiht Mix 1 and Mix 3). With Mix 2 and 4, I push it back to the dead center.

Now my BD3SX rescue auto-levels on my DX8


Congratulations if you made it to the end of this epic.

Hope this helps people.

[Euwan]

Hi

I need some major help with mixing but still can't get my head around it after reading your guide. I would like to use the rudd d/r switch as the aux 2 switch. In the mix menu I have set it to aux 2 to aux 2 then put my settings as -100, 0, -100 and selected rudd as the switch, what happens it goes from one end straight to the other end never stops in the middle even if i put the switch in the middle can you help by any chance?

[ArchmageAU]

Originally Posted by Euwan

Hi

I need some major help with mixing but still can't get my head around it after reading your guide. I would like to use the rudd d/r switch as the aux 2 switch. In the mix menu I have set it to aux 2 to aux 2 then put my settings as -100, 0, -100 and selected rudd as the switch, what happens it goes from one end straight to the other end never stops in the middle even if i put the switch in the middle can you help by any chance?

Sure.

1) Ensure Aux2 is NOT set to any switch in "switch select" in the "system setup" for the model.
2) Remove the mix.
3) Set the governor to be on the Rudd d/r switch.
4) Program the Pos 0, 1 and 2 places with the values you want.

Hope this helps.

[Euwan]

Thanks for this but either I am really stupid or just missing something but I am unable to find governor mode, I am in aeroplane mode if that helps

[ArchmageAU]

Originally Posted by Euwan

Thanks for this but either I am really stupid or just missing something but I am unable to find governor mode, I am in aeroplane mode if that helps

Why are you trying to fly a heli in aeroplane mode? (This also is why governor cannot be found).

The menus change between heli and aeroplane mode.

I assumed that on Helifreak that your TX would be in heli mode.

[Euwan]

Lol my bad should have said before it was for an aeroplane any help with the mixing though?

[ArchmageAU]

Did some experimenting.

Aux2 in acro mode cannot be set directly to a DR switch, but to most others. (Aux2/Gov is the default 3 position switch).

Also using a D/R to turn a mix on an off will only use 2 positions on the switch. 0 = mix off, 1 or 2 = mix on. I can get you 100, -100 (the reverse is just a reversal of the mix numbers - or reverse the channel output).



2 options:

Option 1:

Any mix assigned to Rudd D/R is off when Rudd D/R is 0, and on if Rudd D/R is 1 or 2.

If you set Aux2 to a switch that is permanently in the on position (+100%), Rudd D/R can move that to -100 on activation by using the mix.

Ax2 > Ax2 -100 0 -100 Sw:Rudd D/R (moves Ax2 from +100 to -100, 0 to -100, -100 stays -100)


Option 2:

Unassign Aux2 in the switches (Aux2 will be at 0 as there is no switch to alter it)

Enter in 3 Mixes (in order):
Ax2 > Ax2 0 -100 100 Sw:On (Makes Aux2 +100)
Ax2 > Ax2 0 100 100 Sw:Rudd D/R (Makes Aux2 0 when Rudd D/R 1 or 2)
Ax2 > Ax2 0 100 100 Sw:Rudd D/R (Makes Aux2 -100 when Rudd D/R 1 or 2)


(You may also want to assign your rudder DR to another switch or off).


Sorry I do not have better news to make a 3 pos switch on the Rudd D/R to control Aux2. If I think of another method (without switching from Acro, or internally re-wiring the TX), I will let you know.

[Euwan]

Thank you for all your efforts really appreciate it

[atkin]

bookmarked. this will be great for a rainy day

[Scream]

WOW! >><< (<-mind blown emote)

This is like a heli-tootsie pop! I wonder how many reads until I grasp these magical mixing spells! Bookmarked!!

Thanks for sharing!
-=S=-

[ArchmageAU]

Originally Posted by Scream

WOW! >><< (<-mind blown emote)

This is like a heli-tootsie pop! I wonder how many reads until I grasp these magical mixing spells! Bookmarked!!

Thanks for sharing!

You are welcome.

It's a subtle paradigm shift for most people. Paradigm being "a typical example or pattern of something; a pattern or model.". Paradigm shift being an adjustment on how you think of reality.

Some people get it first read, others take about 5 or more. Depends on how "locked" your preconceptions are.

Most people understand a normal linear mix Aux1 > Aux2 -50,+50 offset 0. As Aux1 changes from -100 to +100, a value from -50 to +50 is added to Aux2. But strange (magical) things seem to happen if + and - are different and offset is also moved. I just try to explain a little of the "magic", but it takes time to get your head around. (i.e. What happens to Aux2 with the mix Aux1 > Aux2 -50,+50 offset +50 when the Aux1 is -75. The answer is Aux2 = Aux2 + (125/100 * -50) = Aux2 - 62.5 {125 is how far -75 is from offset, ie -75+125 = 50 or 125 = 50-(-75))

Don't worry, once you "get" it. It will seem obvious. Then you too can do "magic" .

[ArchmageAU]

Have a correction to the original post after being PM'd by a fellow HF'er.

If you have Governor enabled (so you can set the values of the gov switch, then the channel reverts to "GOV", not "AX2" in the monitor and mix screens.

So:

Originally Posted by ArchmageAU

...
BD3SX rescue with auto level

My X5 mixes are for rescue facility on the BD3SX and mix Aux3 to pull the Aux2 channel to full negative when the Aux3 goes to -100 (Aux3 is assigned to my bind button, Aux2 channel is the BD3SX SL channel and assigned to the Gov switch).

To pull the Aux2 channel to full negative when the Aux3 goes to -100 I use the following single mix.

Mix 6 - Ax3 > Ax2 0% -125% 100% (f.mode N12H)

...

For BD3SX rescue, the mix should be:

BD3SX rescue with auto level

My X5 mixes are for rescue facility on the BD3SX and mix Aux3 to pull the Gov channel to full negative when the Aux3 goes to -100 (Aux3 is assigned to my bind button, Gov channel is the BD3SX SL channel and assigned to the Gov switch).

To pull the Gov channel to full negative when the Aux3 goes to -100 I use the following single mix.

Mix 6 - Ax3 > Gov 0% -125% 100% (f.mode N12H)

I just checked in my DX8 and it says Gov, not Ax2 (like my 130x and nano that have Governor on INH).

Sorry if this confused people.

[Olaf06]

Ugh ... still can't wrap my mind over this.

Can you please put it in a branched formula?

i.e., if x is of this value, this formula is applied, if X is of that value, that formula is applied.

[ArchmageAU]

Originally Posted by Olaf06

Ugh ... still can't wrap my mind over this.

Can you please put it in a branched formula?

i.e., if x is of this value, this formula is applied, if X is of that value, that formula is applied.

Consider the mix (high)50, (low)-10, (offset)0.

For inputs:
-100,-90,-80,-70,-60,-50,-40,-30,-20,-10,0,10,20,30,40,50,60,70,80,90,100

The output ADJUSTMENTS are:
-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,5,10,15,20,25,30,35,40,45,50

(these are the values you ADD to the output channels current value).



If we change the mix to: (high)50, (low)-10, (offset)50

The output ADJUSTMENTS are:
-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,5,10,15,20,25

(we SUBTRACT 50 to the input value (-100 = -150!!!!, -50 = -100, 0 = -50, 50 = 0, 100 = 50), THEN apply the mix)


Therefore, for the master mix for the BD3SX (Ax3 > Ax2 (high)0% (low)-125% (offeset)100%):

If Aux3 was on the knob so it can vary from -100 to +100.

For input values:
-100,-90,-80,-70,-60,-50,-40,-30,-20,-10,0,10,20,30,40,50,60,70,80,90,100

The working adjusted values are:
-200,-190,-180,-170,-160,-150,-140,-130,-120,-110,-100,-90,-80,-70,-60,-50,-40,-30,-20,-10,0

Therefore the Mix adjustments to be added to Aux2 are:
-250,-237,-225,-212,-200,-187,-175,-162,-150,-137,-125,-112,-100,-87,-75,-62,-50,-37,-25,-12,0

(But since the Aux3 switch when assigned to the trainer is either +100(unpressed) or -100(pressed), the only 2 values we worry about are the 0 and -250 adjustments to the Aux2 channel.

These strings of values can be cut and pasted into a spreadsheet to create graphs if you need them. I have purposefully comma separated them.


Last test.

If you have the mix (high)+25 (low)+50 (offset)+38.
You have an input of +18
You have an output of +25
What is the actual output?
.
.
.
.
.
.
.
.
35 !!!! (Originally had 30, but Sonixs found the error)
.
.
.
.
.
.
.
Input of +18 (less offset of 38) is -20
-20 being less than 0 uses the low adjustment
-100/-20 = 0.2 (1/5)
Therefore 0.2 * +50 = 10. So the adjustment is +10. (originally had +25 for high side instead of the +50 which is low side)

25 +10 = 35!!


Sorry this is so confusing, but I have found no easy way of describing this is text (will need to dedicate time to diagrams and graphs to really explain it properly).

[dyin2fly]

ever get the feeling your watching the big bang theory ? lol
(sheldon).

[ArchmageAU]

Bazinga!

Ah gravity, thou art a heartless bitch.

[Tinkrat]

Originally Posted by ArchmageAU

Bazinga!

Ah gravity, thou art a heartless bitch.

THAT right there if funny as hell--LMFAO!!!!
I wish you werent in Oz Arch, I'd gladly ship my DX-8 to you along with a bottle of Pendleton so you could set it up for me!!!

[Sonixs]

I picked up this thread via the bavarianDemon forum and have been chewing on it for a while trying to find the hidden "magic". Thanks ArchmageAU for taking the time to unravel the mystery!

After a few hours of grinding away at your numbers using MS Excel I've a few comments/corrections and would value your input. Perhaps it'll help others understand this too.

Using a formula (will give it later in the post) and running your numbers I totally agree with the following, save for a few decimals which have been left out of your final results ...

Originally Posted by ArchmageAU

Consider the mix (high)50, (low)-10, (offset)0.
For inputs:
-100,-90,-80,-70,-60,-50,-40,-30,-20,-10,0,10,20,30,40,50,60,70,80,90,100
The output ADJUSTMENTS are:
-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,5,10,15,20,25,30,35,40,45,50

If we change the mix to: (high)50, (low)-10, (offset)50

The output ADJUSTMENTS are:
-15,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,5,10,15,20,25

Therefore, for the master mix for the BD3SX (Ax3 > Ax2 (high)0% (low)-125% (offeset)100%):

If Aux3 was on the knob so it can vary from -100 to +100.

For input values:
-100,-90,-80,-70,-60,-50,-40,-30,-20,-10,0,10,20,30,40,50,60,70,80,90,100
The working adjusted values are:
-200,-190,-180,-170,-160,-150,-140,-130,-120,-110,-100,-90,-80,-70,-60,-50,-40,-30,-20,-10,0

Therefore the Mix adjustments to be added to Aux2 are:
-250,-237,-225,-212,-200,-187,-175,-162,-150,-137,-125,-112,-100,-87,-75,-62,-50,-37,-25,-12,0

What I disagree with, using the formula that calculates the previous quoted numbers perfectly, is the following...

Originally Posted by ArchmageAU

If you have the mix (high)+25 (low)+50 (offset)+38.
You have an input of +18
You have an output of +25
What is the actual output?

30 !!!!

Input of +18 (less offset of 38) is -20
-20 being less than 0 uses the low adjustment
-100/-20 = 0.2 (1/5)
Therefore 0.2 * +25 = 5. So the adjustment is +5.

25 +5 = 30!!

I calculate the OUTPUT adjustment as 10, with a total output value of 35.

Working with the following
Master Channel: Max 100%, Min -100%
Mix: High 25% Low 50% Offset 38%
Master Input 18%
Slave Output 25%

Step 1 - Calculate INPUT - OFFSET = 18 - 38 = -20 (Same as your calculation)
Step 2 - Calculate ratio of INPUT - OFFSET based on Master Channel Min = -20/-100 = 0.2 (Same as your calculation, save for a typo where you had = -100/-20 which is 5
I used the Master Channel Min since the INPUT - OFFSET is less than 0; as per your "...-20 being less than 0 uses the low adjustment..."
Step 3 - Calculate OUTPUT ADJUSTMENT for Slave Channel = 0.2 * 50 = 10
I used the Mix Low since the INPUT - OFFSET is less than 0; as per your "...-20 being less than 0 uses the low adjustment..."
Step 4 - Calculate Slave Channel Total Output = 25 + 10 = 35

Are my calculations correct?
Have I discovered the hidden "magic"?

[ArchmageAU]

Originally Posted by Sonixs

....

What I disagree with, using the formula that calculates the previous quoted numbers perfectly, is the following...


I calculate the OUTPUT adjustment as 10, with a total output value of 35.

Working with the following
Master Channel: Max 100%, Min -100%
Mix: High 25% Low 50% Offset 38%
Master Input 18%
Slave Output 25%

Step 1 - Calculate INPUT - OFFSET = 18 - 38 = -20 (Same as your calculation)
Step 2 - Calculate ratio of INPUT - OFFSET based on Master Channel Min = -20/-100 = 0.2 (Same as your calculation, save for a typo where you had = -100/-20 which is 5
I used the Master Channel Min since the INPUT - OFFSET is less than 0; as per your "...-20 being less than 0 uses the low adjustment..."
Step 3 - Calculate OUTPUT ADJUSTMENT for Slave Channel = 0.2 * 50 = 10
I used the Mix Low since the INPUT - OFFSET is less than 0; as per your "...-20 being less than 0 uses the low adjustment..."
Step 4 - Calculate Slave Channel Total Output = 25 + 10 = 35

Are my calculations correct?
Have I discovered the hidden "magic"?

You are correct. I should have taken the low side of the mix (+50 instead of +25 which was the high side).

0.2*50 = 10 so the output is 35.

You are correct (and get the elephant stamp - or at least a rendition of "soft kitty").

[Sonixs]

Originally Posted by ArchmageAU

You are correct. I should have taken the low side of the mix (+50 instead of +25 which was the high side).

0.2*50 = 10 so the output is 35.

You are correct (and get the elephant stamp - or at least a rendition of "soft kitty").

Woohoo!
Thanks again for clarifying the mystery behind Spektrum Mixing, it's not so bad when you get your head around it!


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