Spektrum DX7 Programming Notes
Introduction and Brief Review
The Spektrum DX7 is the first full-range 2.4 GHz system to hit the market. I wrote a review in the April issue of RCMW, and found it to be a reasonably well featured system (if not quite as flexible as some other 7-channel radios), nicely constructed, and with a rock solid radio link.
Downsides were the poor balance of the box, rather archaic programming (though by no means worse than some other Far Eastern radios), and the need to install two receivers in the model.
The virtually interference proof spread spectrum link is what makes it so attractive, however, and the set has become very popular here in the UK.
Here are some programming notes which owners may find useful.
- Programming four-servo wings
- Throttle 'kill' function
- other information.
Programming 4-Servo Wings
Support for 4-servo wings is becoming essential in mid-range radios, due to the increasing popularity of 3D electric models and advanced sailplanes. While the DX-7 only supports 2-servo wings via stock mixers, the extra two servos can be driven using the PMIX (programmable mix) functions - and a bit of effort.
My scheme provides the following mixes:
- 4-servo Aileron
- 4-servo Camber
- 4-servo Snapflap
Here are the steps involved in setting this up.
STEP 1: Set Flapperon Wing
in the System menu, set the model type to ACRO, and the wing type to Flapperon (and optionally enable the V-tail mixer).
STEP 2: Servo Assignments
Connect the servos to the following channels. The wing servos are shown in purple - chs 2 and 6 are assigned to the inner surfaces ('flaps'), while chs 5 and 7 are assigned to the outer surfaces ('ailerons').
| Rx Channel | Connect this Servo | |
| 1 | THRO | Throttle |
| 2 | AILE | Right Inner |
| 3 | ELE | Elevator |
| 4 | RUDD | Rudder |
| 5 | GEAR | Left Outer |
| 6 | FLAP | Left Inner |
| 7 | AUX2 | Right Outer |
STEP 3: Disable the 'Gear' switch
The Gear function must be disabled, so it doesn't affect channel 5.
- Enter the SERVO TRAVEL menu
- Set the servo travel for 'Gear' to zero/zero.
STEP 4: Set up the Flap system
The DX-7 provides a choice of activation method for flaps. The 'System' option will suit most pilots. It provides a choice of three flap presets, selectable via the flight-mode switch.
- Enter the SYSTEM->INPUT SELECT menu.
- Select 'system'.
- Set FLAP TRIM=INH
STEP 5: Set up the mixers
In the final step, we'll set up the stock mixers for the inner surfaces, with PMIX's for the outer.
| Function | Mixer Menu | Rate | Offset |
| Inner Snapflap | [ELEV->FLAP] | D=0/U=+10 | n/a |
| Inner Camber | [FLAP SYS] | NORM=0 MID=10 LAND=15 |
|
| Inner Aileron | [D/R] (to set travel) | ||
| Outer Snapflap | [PMIX3]: Elev->Gear | 0/+10 | 0 |
| [PMIX4]: Elev->Aux2 | 0/+10 | 0 | |
| Outer Camber | [PMIX1]: Flap->Gear | +100/+100 | 0 |
| [PMIX2]: Flap->Aux2 | +100/+100 | 0 | |
| Outer Aileron | [PMIX5]: Aile->Gear | +100/+100 | 0 |
| [PMIX6]: Aile->Aux2 | -100/-100 | 0 |
Notes
- PMIX5/6 must be used for the outer-aileron mix in order for the aileron trim lever to work.
- Aileron travel is set in two places:
- Dual Rate. This adjustment affects all four servos.
- PMIX5/6. This adjustment affects outer surfaces only.
- Differential is adjusted differently for inner and outer surfaces:
- For inner surfaces, use the Diff menu.
- For the outer surfaces, set different up/down rates in PMIX-5 and PMIX-6.
Crow Mixing
Many glider pilots will be wondering whether the DX-7 can be used for crow brakes. Well yes it can, but the programming is very tricky. OK I'll be honest, it's actually pretty horrible especially if you're used to the adjustabilty of a Multiplex radio as I am.
The problem is (a) lack of PMIX's (this means that some of the mixes above have to be dropped) and (b) the puzzling - and undocumented - behaviour of the Offset parameter in the Throttle mixes (PMIX1 and PMIX2 below). This makes it very tricky if not impossible to set the crow travel accurately on the outer surfaces (it's easy enough on the inner flaps).
For what it's worth, here's my attempt. In order to free two PMIX's for crow, I've dropped two of the outer surface mixes, namely, snapflap and camber.
| Function | Ch | Mixer Menu | Rate | Offset |
| Inner Snapflap | [ELEV->FLAP] | D=0/U=+10 | n/a | |
| Inner Camber | [FLAP SYS] | NORM=0 MID=10 LAND=15 |
||
| Inner Aileron | [D/R] (to set travel) | |||
| Inner Crow | [PMIX3]: Thro->Flap | +50/+50 | +100 | |
| Outer Crow | [PMIX1]: Thro->Gear | +50/+50 | -100 | |
| [PMIX2]: Thro->Aux2 | +50/+50 | -100 | ||
| Crow/Elev Compensation | [PMIX4]: Thro->Elev | 0/+25 | 0 | |
| Outer Aileron | [PMIX5]: Aile->Aux2 | +100/+100 | 0 | |
| [PMIX6]: Aile->Gear | -100/-100 | 0 |
Summary
It is possible get a basic 4-servo wing up and running - just. Proper crow brakes are not really practical though. The DX-7 also lacks flight modes and curves, which are almost essential for 6-servo sailplanes (if not for fun-fly electrics).
It's worth pointing out that many gliders will also have installation issues, due to space requirements of the twin AR7000 receiver. (While some modellers are using park-fly AR6100 receivers in full range applications, beware that this is specifically not recommended by the manufacturer.)
Implementing a Throttle Kill function
There is no throttle kill function provided with the DX-7, instead there's 'Throttle Idle Recovery'.
For those who prefer a traditional Kill function, here's a solution which works off the MIX switch:
- Use PMIX-5 or PMIX-6
- mix THRO->THRO
- SW=MIX
- Rate = -100 / -100 (note both negative)
- Offset = -125 (note negative)
Note 1: use only PMIX-5 or 6, otherwise the kill setting will vary with idle trim.
Note 2: The kill position is adjusted via Offset.
Channel Assignments
Table below shows channel assignments of the DX-7.
| Wing Type | |||||
| Ch # | Normal | Flapperon | V-tail | Delta | Notes |
| 1 | Throttle | ||||
| 2 | Aileron | Flapperon | Elevon | ||
| 3 | Elevator | Vtail | Elevon | ||
| 4 | Rudder | Vtail | |||
| 5 | Gear | ||||
| 6 | FLAP | Flapperon | labeled as 'AUX1' on AR7000 | ||
| 7 | AUX2 | ||||
Mixing Architecture
The mixing architecture is quite simple, but not explained in the manual.
Mixers: Simple case
Consider a mixer C1 -> C2, e.g. THRO -> ELEV
In the simple case (e.g. for Normal wing type), moving stick C1 will effect just the channel corresponding to C2. So with THRO -> ELEV mixer, moving the throttle stick will modify the signal to servo #3 .
Mixer: special cases
Things are only a little more complicated for the special wing types. Again, consider a mixer C1->C2. The table below shows the effect of different C2 and wing types:
| Wing Type | C2 | Output Channels | Relative sense |
| Flapperon | AILE | #5, #6 | opposite sense |
| FLAP | #5, #6 | same sense | |
| Delta | AILE | #2, #3 | opposite |
| ELEV | #2, #3 | same | |
| V-tail | RUDD | #3, #4 | opposite |
| ELEV | #3, #4 | same |
Examples for wing type = Flapperon
- Rudd -> Aileron
- In this case, C2=Aileron. Looking at the table above for a Flapperon wing, shows that displacing the elevator stick causes the flapperons to move in opposite senses. This mix would therefore be suitable for for roll correction in knife edge.
- Elev -> Flap
- Here, C2=Flap. Displacing the elevator stick causes flapperons to move in the same sense. Use this for 'snapflap' effect.
Pulse Widths
Aileron channel, trim at centre, all settings at default values. Measured using servosim.
| Servo Travel | Min (mS) | Max (mS) |
| +50/+50 | 1.3 | 1.7 |
| +100/+100 | 1.1 | 1.9 |
| +125/+125 | 1.0 | 2.0 |
| +150/+150 | 0.9 | 2.1 |
Interestingly, the DX-7 outputs eight (not seven) channels at the DSC interface.