Taranis OpenTX Elevon Mixing

Here's how to mix elevons on Taranis using OpenTX.

It's a pretty straightfoward procedure:

• mix the elevator stick on both channels.  The value will be either 50% or -50%, depending on how your servos are set up.  If the control surfaces move in the wrong direction, swap the sign.
• mix the aileron stick on both channels.  The multiplex parameter will be "add", and the values will also be 50% or -50%.  Proper motion:  when the stick moves left, the left control surface should raise and the right control surface should lower.  Vice versa for moving the stick right.

Here's some notes on how elevon mixing works:

http://eastbay-rc.blogspot.com/2011/05/v-tail-mixing.html
http://eastbay-rc.blogspot.com/2011/05/elevon-v-tail-mixing-calculations.html

Here's my mix.  Yours should be the same, possibly swapping out the positive/negative values.

Ch 2  Ele    50%
  +=  Ail   -50%
Ch 3  Ele   -50%
  +=  Ail   -50%

er9x: Elevon Mixing (good for Turnigy 9xr)

Here's some notes on elevon mixing with er9x.  It's pretty simple once you know the basics.  Here's some background on how elevons work.  Check out the calculations page... I think it's the only page on the Web with the mixing formulas -- at least as far as I could find!

• http://eastbay-rc.blogspot.com/2011/05/v-tail-mixing.html
• http://eastbay-rc.blogspot.com/2011/05/elevon-v-tail-mixing-calculations.html

Here's the mix.  The right and left elevons are on channels 2 and 3, respectively.  Note that the +/- values of the mix will be determined by the servo installation, so follow the technique on the video to make sure nothing is reversed.

2    100% ELE
  + -100% AIL
3   -100% ELE
  + -100% AIL

Here's a general introduction on er9x mixing:

• http://eastbay-rc.blogspot.com/2012/12/er9x-tutorial-mixing-good-for-turnigy.html

Here's some notes on elevon mixing for the DX6i and Stock 9x.  It's interesting to compare the different approaches.

• http://eastbay-rc.blogspot.com/2010/07/dx6i-elevon-mixing-for-superfly.html
• http://eastbay-rc.blogspot.com/2012/08/turnigy-9x-elevon-mixing.html

Here's an express version of the video:

toc: Elevons, er9x

Turnigy 9x Elevon Mixing

 Later I'll add some more verbiage and perhaps even make a video, but for now here's the two screens you need to fiddle with in order to get Elevon mixing going on a Turnigy 9x.

First, set the aileron endpoints to 120% in each direction.  Move the aileron stick left and right to get to the two numbers.

[update: I thought I got this idea from Andreas, but he sent me an email asking about this and claiming never to have done it.  Did I hear about it on RCG?  Make it up out of whole cloth?  Investigation forthcoming!]

Once you've got the endpoints set, go to the Elevon menu and set it to look something like this.  Depending on how your servos are installed, swap the values 100 and -100 until you get things right.

Here's what Elevon mixing does, and how it's calculated.




This space reserved for a video of this.  Will Mark get to it?  The suspense will kill you!
Update: yes he did!

Elevon Gyro Stabilization

Scott Page has an interesting post on rcgroups where he has mounted gyros on a superfly.

It seems like this couldn't be done without moving the elevon mixing onto the plane, since there's not a direct correlation between axial pitch and roll movement and the control surfaces.  The trick is to put two gyros mounted at 45 degrees relative to the front of the plane, and connect the gyros to the servos on the opposite side of the frame.

By doing this, both servos react to pitch and roll, and feed their corrections to the proper (opposite) elevon.

He put a video up with the results of his experiments.  He also talks about rate and AVCS (heading hold) modes and their use in fixed wing flight.  Executive summary: use rate.

Elevon / V-Tail Mixing Calculations

update: moved this into its own post.  original elevon description here.

Calculating Elevon Motion

There are two calculations, one for each elevon:

        a = x/2 - y/2
        b = x/2 + y/2

where

•  a = left elevon deflection,
•  b = right elevon deflection,
•  x = aileron position (-1 = far left, 0 = centered, 1 = far right),
•  y = elevator position (likewise, -1 .. 1)

Deriving the Elevon Calculation

I couldn't find the above formula anywhere on the web, probably because it's so obvious to everybody but me.  Here's how I figured it out.  Real mathematicians would do it much easier I'm sure!

First, look at the inputs and outputs.  The above video shows the endpoints and midpoints of the two axes.

which gives us this table for the values of A and B:

    a,b = f(x,y):
                 x=-1.0       x=0.0         x=1.0
        y=1.0    -1.0, 0.0    -0.5, -0.5    0.0, -1.0
        y=0.0    -0.5, 0.5     0.0,  0.0    0.5, -0.5
        y=-1.0    0.0, 1.0     0.5,  0.5    1.0,  0.0

Showing only the values for A, we notice that there's a pattern across the rows, namely that it increments by .5 each row, as X varies from -1 to 1.  So, we can start with "+ x/2" for each of the rows, for some value of Y.

    a = f(x,y):
        -1.0    -0.5    0.0
        -0.5     0.0    0.5
         0.0     0.5    1.0

Likewise, we can see the same pattern for the columns in the other direction.  Fiddling a bit, I came up with -y/2 + x/2 which of course simplifies to x/2 - y/2.  I guessed there was a similar pattern for B, and tried a few variations of adding and subtracting x/2 and y/2. until I confirmed that x/2 + y/2 worked.

Here's a bit of python that reproduces the table above:

    for x in (-1.0, 0.0, 1.0):
        for y in (1.0, 0.0, -1.0):
            a = x/2 - y/2
            b = x/2 + y/2
            print a,
            print b,'\t\t',
        print

Elevon / V-Tail Mixing

Here's what an Elevon or V-Tail/ mixer does.  You can do it with your radio if it has that feature, or with an electronic hardware mixer.  Here's the HobbyKing Mixer in action:

If you're hardcore old school, you can do pure hardware mixing with this Dubro V-Tail kit ("23 piece kit").  NightFlyyer has a nice video (where??) showing one of his classic planes with hardware mixing.

Elevon Action

The elevator control will move both elevons equally up or down.  When the aileron control is centered, pull the elevator back, then push it forwards.  You will see the elevons go up, then down.  The plane will be level across the wings, and pitch up and down.

The aileron control will move the elevons in the opposite direction.  With the elevator centered, move the aileron control left, then right.  When the stick is to the left, you will see the left elevon move up and the right elevon move down.  When the stick is to the right, the left elevon will be down and the right elevon will be up.  The plane will be level, rolling left and right.

When both the elevator and aileron move, the elevons combine the motion of the two.  For example, pull the aileron left; you will see the left/right elevons move up/down.  Keeping the aileron left, pull the elevator back.  Both elevons will move up the same amount, keeping the deflection set by the aileron.

Motion Rules:

• elevator back: elevons up
• elevator forward: elevons down
• aileron left: left elevon up, right elevon down
• aileron right: right elevon up, left elevon down

Elevon Equivalence

The same calculations for translating aileron/elevator to elevon wing surfaces will translate joystick controls to tank-style left/right wheel/tread motion.

Calculating Elevon Motion

update: I moved this to its own post, here.

Dx6i Elevon Mixing for SuperFly

Update:  Superfly Guru Hance over at RCGroups has a better solution than the one I originally used. Here it is.  I've gone through the steps below and verified it works great... Thanks Hance!


Transmitter: Spektrum DX6i
Receiver: OrangeRX Spektrum DSM2 6ch

Reset Memory

• Start by resetting the settings for this model:
  [MENU / SETUP LIST (9)/ COPY/RESET (12) / RESET]
• This only resets one model memory, not the entire DX6i. 
• This resets your model name as well.

Receiver Setup

• Engine (ESC) to throttle.
• Right (starboard) servo to aileron.
• Left (port) servo to AUX1.

Left Stick

• Nothing needs to be done.
• Throttle will work as expected.
• Rudder channel not used.

Aileron Control

• At this stage, only the right elevon should move.
• Aileron right:  right elevon up.
• If the right elevon moves down, reverse the aileron controls:
  [MENU / SETUP LIST (9) / REVERSE (4) / AILE-R]

Elevator control

• Move elevator up and down.
• Nothing should happen at this time.

Wing Tail Mix

• Set the wing tail mix to "dual aileron" mode:
  [MENU / SETUP LIST (9) / WING TAIL MIX (6) / DUALAILE ACT]

Check control surfaces again

• Aileron stick right: right elevon up, left elevon down.
• Aileron stick left: left elevon up, right elevon down.
• If left elevon motion is backwards, reverse flap channel:
  [MENU / SETUP LIST (9) / REVERSE (4) / FLAP-R]
• If right elevon motion is backwards, reverse aileron channel:
  [MENU / SETUP LIST (9) / REVERSE (4) / AILE-R]

Elevator

• Set MIX 1 to active:
• [ MENU / MIX1 (6) / ACT ]
• This will give you a new menu for MIX 1.
• Change first row to: ELEV -> FLAP ACT.
• Change second row to: RATE D -100% U -100%.
• You may need to set the rate to +100% if the servos are reversed.
• Change third row to  SW ON TRIM ACT.

Final Test

• right stick:  right elevon up, left elevon down
• left stick:  left elevon up, right elevon down
• stick back:  both elevons up
• stick forward: both elevons down

"Classic" Dx6i Mixing

Here's the "standard" instructions for the Dx6i

Here's the steps I used to set elevon mixing with my Dx6i / Superfly combo.  Thanks to  brandonrc for his YouTube walkthrough that explained about using Mix1 and Mix2.

todo: another rcgroups discussion, are they in agreement?
    Spektrum DX6i Elevon Weirdness: Worse Than You Think
         Fix For Elevon Routines

Radio Hardware

• transmitter: Dx6i
• receiver: 6110e

Servo Connections

• Left servo, connect to ELEV
• Right servo, connect to AILE

Set Elevon Mode

• menu: ADJUST LIST / SETUP LIST (9) / WING TAIL MIX (6)
• set ELEVON = ACT (all others INH)

Set Proper Reverse (I haven't heard anybody else mention this, but if I didn't reverse AILE then the controls were rotated 90 degree, i.e. which I mean elevator and aileron controls were swapped.)

• menu: ADJUST LIST / SETUP LIST (9) / REVERSE (4)
• set AILE = R (all others =N)

Get Full Servo Throws:

• menu: ADJUST LIST / MIX 1 (6)
• set ELEV -> ELEV ACT
• set RATE D = 125%
• set RATE U = 125%
• set TRIM = ACT
• menu: ADJUST LIST / MIX 2 (7)
• set AILE -> AILE ACT
• set RATE D = 125%
• set RATE U = 125%
• set TRIM = ACT 

125% is the maximum mix adjustment you can select.  The SuperFly manual recommends starting with throws of 1.5 inches up and 1.5 inches  down and adjusting to taste, so use whatever value gives you the control you like.