Multiplex Heron – Build Report – Programming The DX9 Transmitter

Last Change: 26.06.2017   

[⇐ Power Supply] | [⇑ Overview]

Concepts & Features

Our transmitter is a Spektrum DX9 in mode 2, throttle and rudder on the left hand side. We are using the Spektrum AR7350 receiver with an internal AS3X stabilisation system. This will impose some awkward restrictions to the programming of the transmitter. So be it! The Heron is our first model to make use of a full-fledged home-made AS3X configuration.

However, mastering the AS3X ist not our only quest. The features we want to implement are:

  • The throttle stick is used either for the motor or the butterfly configuration depending on the flight mode.
  • 4 flight modes are available: Launch (with motor), Cruise, Speed and Thermal. The latter three without motor but with butterfly.
  • Telemetry for receiver voltage, flight pack voltage, AS3X settings.

Addendum 08.05.2017: We had to learn that AS3X would not let you program the ailerons individually. There is no way (known to us) of making them both deflect to the same direction at the same time, as their ports are hogged completely by the AS3X system. So there is no aileron support for the butterfly configuration. However, we decided to stick with the AR7350 and lowered our expectations …

Getting Started

As some of the programming work needs to be on the transmitter and some of it on the receiver, it might become hard to tell what exactly is going to happen at the receiving end of the servo leads. Real end-to-end testing is mandatory.

This is where the good old test rig built earlier for our E Tomcat comes in handy. It will save us the trouble of having a 2.4 metre glider lying on the desk while fiddling with the programming of the DX9 and the AR7350 intermittently. It will also avoid “flightless” operating hours on the clock of the expensive built-in components of the model. And believe me, it may take hours …


Basically, it is just a 6 millimetre plywood sheet with three pieces of batten as a stand. Drill and saw a few holes into it and you are done. The servos are of the cheapest variety. They are bolted to the rig permanently for reuse, whereas the other components are attached to it just during the tests, using bolts, cable ties or velcro straps as applicable.


Basic Model Setup For AS3X

Intermezzo: Spektrum tells you, when AS3X is to be used, to create a new Airplane type model on the transmitter, even if your model is a glider.  That is exactly what we were not going to do at our first attempt. We wanted to set up a glider based on the glider functions of the DX9. Some of these features would not have been available if the model was created as airplane type.

So we dared to select Sailplane, accepting the challenge that the initial receiver port assignments of the DX9 did not match those expected by the AR7350 receiver. We corrected the assignments and made quite some headway. Unfortunately, we only got as far as to the Spektrum Programmer App telling us to select the “1 Aileron 2 Flap” setting on the transmitter to achieve a correct 2-ailerons-2-flaps configuration on the receiver. This option is not available for sailplanes. – Dead end street!

Airplane it shall be this time. And we have to adopt a new thinking: Trimming and mixing with AS3X is (mostly) done on the receiver, not on the transmitter.

 Menu: System Setup → Model Select →
  1. Do you want to create a new model?  → [CREATE]
 Menu: System Setup → Model Type
  1. Model Type → [Airplane]
    Must be Airplane, as learned above.
  2. Confirm Model Type
 Menu: System Setup → Model Name
  1. Name: → “Heron”
    … or whatever you like.
 Menu: System Setup → Aircraft Type
  1. Wing: → [1 Ail 2 Flaps]
    There are 2 servos for the ailerons, but this will be configured on the receiver.
  2. Tail: → [Normal]
 Menu: System Setup → F-Mode Setup
  1. Switch 1: → [Switch H]
    Switch has 2 positions.
  2. Switch 2: → [Switch G]
    Switch has 3 Positions

There are 4 flight modes enabled by the combination of these two switches (not 6 as one would expect). The modes as named FLIGHT MODE 1, 2, 4 and 5.

 Menu: System Setup → Spoken Flight Mode
Actuate switches H and G to display the four flight modes on the screen and adapt properties accordingly. We will reuse mode names and sounds already available on the DX9.

  1. Switch H [down] → FLIGHT MODE 1
    F-Mode name: “Launch”
    Speak: [Launch]
  2. Switch H [up] and Switch G [down]: → FLIGHT MODE 2
    F-Mode Name: “Speed”

    Speak: [Speed]
  3. Switch H [up] and Switch G [center]: → FLIGHT MODE 4
    F-Mode Name: “Cruise”

    Speak: [Cruise]
  4. Switch H [up] and Switch G [up]: → FLIGHT MODE 5
    F-Mode Name: “Thermal”

    Speak: [Thermal]

Throttle Stick For Butterfly (And More)

We want the motor to be active in launch mode only. So the throttle stick will not start or control the motor unless switch H is in its downward position. We use the throttle cut feature of the DX9 to shut down the motor when H is up.

 Menu: Function List → Throttle Cut
  1. Position: → “-100” %
  2. Switch: → [Flight Mode]
  3. Four squares numbered 1, 2, 4 and 5 representing each flight mode will appear. Make sure that squares 2, 4 and 5 are displayed inverted (throttle cut on) while 1 is normal (throttle cut off).
  4. Delay: Inh.

This was the easier part. Now we need to have a closer look at the current receiver port assignments and their respective inputs on the DX9.

Menu: System Setup  → Channel Assign

Rx Port Assignments
Port # Port Name Channel (Standard) Channel (Modified)
1 THRO Throttle
2 AILE Aileron
3 ELEV Elevator
4 RUDD Rudder
5 GEAR Gear
6 AUX1 R Flap
7 AUX2 L Flap
8 AUX3 Aux 3 Inhibit
9 AUX4 Aux 4 Inhibit

Note that the Gear channel is on port 5. This is where the AR7350 receiver expects to get the flight mode data. We leave it as it is, even though the term Gear may be misleading.

Ports 6 and 7 are used for the flaps. We want to control them with the throttle stick. So we change the standard channels from L Flap / R Flap to … ? Do not be tempted to make them listen to the Throttle channel, which is also available here. Due to the throttle cut we implemented above, the Throttle channel will be inactive when the current flight mode is anything other than Launch. Do not change anything here for the flaps.

Just for safety reasons we switch off ports 8 and 9 by setting them to Inhibit.

Menu: System Setup  → Channel Assign → NEXT

On this screen we can see and maintain which inputs (switch or other device) feed the channels. Only a few of them can be changed.

Channel Input Config
Channel # Channel Name Input (Standard) Input (Modified)
6 AUX1 N/A
7 AUX2 N/A
8 AUX3 RKnb
9 AUX4 LLv Thr

The GEAR channel is changed from switch A to switch G, which is our flight mode switch for modes Cruise, Thermal and Speed.

The AUX4 channel will now take its input from the trottle stick. However, AUX4 has nothing to do with the THRO channel, except for the shared stick. So what is it good for? The AUX4 channel does not go to any port and therefore will not make its way to the flap servos of the model. Unless, of course, we mixed it to some other channels, which in this case would be L Flap and R Flap.

 Menu: Function List → Mixing → P-Mix 1
  1. [AX4] > [LFL]
  2. Rate: -125%  -58%
  3. Offset: -22%
  4. Switch: Switch H
    downward position [off] (normal)
    upward position [on] (inverted)
 Menu: Function List → Mixing → P-Mix 2
  1. [AX4] > [RFL]
  2. Rate: 0%  0%
  3. Offset: 0%
  4. Switch: Switch H
    downward position [off] (normal)
    upward position [on] (inverted)

If it was not for the activation of the mixes with the H switch, we could have linked the Aux 4 channel directly to the flap ports 6 and 7.

Overview Stick & Switch Functions

Stick/Switch Flight Mode Function
Throttle Launch throttle
Thermal, Cruise, Speed butterfly
Rudder all rudder
Elevator all elevator
Aileron all aileron
A, B, C, D, E, F n/a not used
G n/a flight modes (2)
0 = Speed
1 = Cruise
2 = Thermal
H n/a flight modes (1)
0 = Launch
1 = flight modes (2) + throttle cut
I all vario on/off
R KNOB n/a not used

[⇐ Power Supply] | [⇑ Overview]

2 thoughts on “Multiplex Heron – Build Report – Programming The DX9 Transmitter

  1. Pingback: Multiplex Heron – The Unboxing | Flying Tom's Blog

  2. Pingback: Multiplex Heron – Das Unboxing | Flying Tom's Blog

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s