Multiplex Cockpit MM

DLG Modifications

by Jay Decker

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Disclaimer

Background and Objectives

Like many handlaunch pilots, I liked the feel of the Multiplex Cockpit MM transmitter the first time I picked it up. It is light, thin and the recessed cavity in the back of the case fit great in my hand and made the transmitter easy to hang on to.

As they say, "the devil is in the details". Upon further study, what had initially appeared to me to be the ultimate DLG transmitter had some severe programming short comings, since it had no elevator and rudder preset capability. Upon detailed study, I discovered that both elevator and rudder presets could effectively be implemented for rudder and elevator planes by plugging the rudder servo into the aileron servo position and programming the transmitter for a plane with flaperon actuation with elevator compensation mixing. By assigning the "flaperon" to be deployed by a switch, one could achieve rudder preset because the rudder would move as an aileron and elevator would move due to flaperon-elevator compensation mixing. This works just fine for rudder-elevator planes, but not DLG planes with flaperons.

The Cockpit transmitter modifications below are intended to achieve elevator and rudder preset on DLG planes with flaperons. With the modifications listed below I've gained rudder and elevator presets that are programmable, i.e., that can be set and stored individually for each model memory with some unconventional programming. However, I lost dual rate and some motor/time functionality, but these are functions I do not use or can live without.

Transmitter Modifications

Here are the Cockpit modifications necessary for implement rudder and elevator presets for DLG planes with flaperons:

1. Install a new DPDT momentary (spring loaded) switch in the upper left hand (for right handed throwing) corner of the transmitter.

2. Install a 5K Ohm trim pot to create voltage signal to send the transmitter equal to the rudder stick voltage signal for full right rudder (for right handed throwing).

3. Wire the switch and trim pot into the transmitter to achieve the following when the momentary switch is actuated:

• Replace the rudder stick signal with the full right rudder signal generated by the trim pot. This effectively gives you full right rudder preset when the switch is actuated.

• Turn on dual rates. Turning on the dual rates while the switch is actuated and the transmitter is fed full right rudder allows the amount of rudder preset to be set by programming the desired amount of rudder dual rate.

• Turn on the motor. The Cockpit transmitter has an elevator compensation mixer for the motor on switch ("PWR-CO" under the mixer menu). Turning on the motor feeds the signal to this mixer that allows the motor-elevator compensation mixer to create an elevator preset.

Cockpit transmitter modifications

Photo 1: Modified Cockpit transmitter 

Items shown in Photo 1:

1. Dual rate switch supplied with transmitter insulated and taped to transmitter case for storage.

2. "Combi" (coupled aileron and rudder) switch moved from left most position to this position, since I wanted the DLG preset switch in the left most position.

3. The new DPDT momentary "DLG" preset switch.

4. 5K Ohm trim pot attached to epoxy board.

5. The epoxy board supporting the trim pot is attached to the transmitter with a gimble mounting screw.

6. Control A input connector (the rudder stick input).

7. Switch S1 connector (motor input).

8. Switch S2 connector (dual rate input)

Photo 2: Front after modifications

Items shown in Photo 2:

1. "DLG" preset switch. The silicon tubing helps grip the switch during quick turnarounds.

2. "Combi" (coupled aileron and rudder) switch.

Programming Quirks

1. The transmitter configuration is set to "Stick Mode 6".
2. The amount of rudder preset is determined by setting the appropriate rudder dual rate setting while the DLG preset switch is actuated. The dual rate switch state is changed for ailerons, elevator and rudder  every time the DLG preset switch is actuated (it is normal for a single switch to change the dual rates for all three controls in the Cockpit). So, I set the dual rates for everything to 100% at both DLG preset switch positions before beginning programming and only adjust the appropriate rudder dual rate setting to adjust rudder launch preset.
3. The amount of elevator preset is determined by the power-elevator compensation mixer, "PWR-CO" mixer. Make sure that the flaperon switch is in the center position. Flaperon-elevator and spoiler-elevator compensation mixing can over rider the motor-elevator compensation mixing.

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