Tutorials : mc4000 - Flight Modes, T switches, and Presets

Mike Shellim March 2006

Introduction

The 4000 has simple but highly flexible Flight Modes feature. Let's look at this important topic in more detail, and see how it can be further enhanced using presets and transfer switches.

Flight Modes overview

Flight modes provide a quick way for the pilot to switch between different control settings during flight. For example with a tow-launch glider, different amounts of elevator trim and travel may be required for launch and landing. By switching between flight modes, the pilot can quickly call up the correct settings.

(Note that flight modes store control settings, not servo settings. You cannot store mixer curves, or servo centres per flight mode.)

Which Adjustments are Stored per Flight Mode?

The Controls Reference shows all the settings which are be stored per flight mode. When altering any of these settings (in the Adjust Controls menu), the active flight mode is displayed at the top. When altering a setting, make sure you switch to the relevant flight mode before making the adjustment.


Adjust Controls menu for Spoiler/FIXED_VAL.
The top line shows the active flight mode ('F3F') to which this adjustment applies

Flight mode switches

There are five flight modes available on the 4000. Flight mode 1 is active when a model is created initially. The other flight-modes (numbered 2 thru 5) are intially Off.

To enable any of flight modes 2 to 5, a switch must be assigned to it. The flight mode becomes active when the switch is On.

If three of more more flight modes are used, you will almost certainly wish to use a 3-position switch. In that case, it will be necessary to create a T (transfer) switch. So let's see how to set up a T switch.

Transfer (T) switch overview

If you wish to use a 3-position switch switch as a secondary switch e.g. for flight mode selection, it is necessary to create a virtual transfer ('T') switch first. A Transfer switch appears as three separate on/off switches in the menus, designated Tn-1, Tn-2 and Tn-3. These represent the bottom, middle and top positions of the actual 3-position switch. In effect, each position of the 3-position switch is represented by its own on/off switch! This may seem a little odd but it's actually extremely useful.

Consider a transfer switch T1 associated with a real 3-position switch.

You can reverse the sense of a switch by pressing the R button in the appropriate menus. Taking T1-1 for example, when reversed it will be active when the switch is in the up or middle positions, and inactive when it's down.

You make the association between the 'real' and 'virtual' switches in the Assign Switches menu. For example, To set up a transfer switch T1 based on a 3-position switch plugged into S01, follow these steps:

  1. Enter the Assign Switches screen
  2. Select the T1 switch from the list of switch types
  3. Select the real switch SO1


Transfer switch T1, based on 3-position switch SO1

Flight Mode Priorities

If multiple flight modes are set up with different switches assigned, then it is possible that two or more flight modes might be active at the same time. To resolve such conflicts, each flight mode has a priority. If more than one flight mode is selected, the flight mode with the highest priority 'wins'. The priority is the same as the flight mode number in the Flight Phase menu.

The default flight mode (#1) is always On, but since it has the lowest priority, it will always be over-ridden if another flight mode is activated.

Setting up a flight mode

Having set up a T switch, we're ready to set up some flight modes. This is done in the Flight Phase menu. The figure in the top left corner is the priority. The activation mode is shown in the bottom right corner. The bottom left corner specifies the transition time.

In the following example, we have have already set up a T switch. We use it to select between three flight modes 'F3F', 'Thermal' and 'Landing".



Flight modes F3F (priority 1), Thermal (4) and Landing (5), all driven by 3-pos switch T1.

 

Note:

To summarise:

Adding a fourth Flight Mode

Suppose now we want to add a fourth Aerobatic flight mode. We've already used a three position switch, so we must use a second switch for this. Let's use a 2-position switch SO2.

Let's have Aerobatic mode override F3F, but not override Thermal and Landing modes. Aerobatic therefore needs a priority between 1 and 4, so we'll use flight mode 3.

This is the screen for flight mode 3:


Aerobatic flight mode, priority 3, driven by SO2

So now

Presets and FIXED_VAL

You may notice in the controls reference, that some controls have a FIXED_VAL setting. This is available for throttle, spoiler, flap and tow-release and some other controls. FIXED_VAL is a simple way of implementing what in other R/C systems are called presets.

When a control's FIXED_VAL setting is active, the control takes on a fixed position, over-riding the actual stick position. This fixed position depends on the value of FIXED_VAL entered by the user. A value of -100 represents one stick end point, zero represents centre stick, and +100 representing the other end point.

How to set up FIXED_VAL

The procedure for setting up FIXED_VAL is:

  1. Enter the Adjust Controls menu
  2. Select the control (e.g. Spoiler, Flap, Towhook etc.)
  3. Switch in the target flight mode (the one you want the FIXED_VAL setting stored in).
  4. Choose the FIXED_VAL option.
  5. Set the FIXED_VAL value between -100 and +100
  6. Set the FIXED_VAL activation mode to On, Off, or a switch.

FIXED_VAL Activation mode

Setting the Activation mode to ON means that the control permanently takes on the fixed value specified by the user.

Setting it to OFF means that the control operates normally, via the widget assigned to it.

You can also activate FIXED_VAL via a switch. However, it's more common to set the activation mode to On or Off, and to select a particular FIXED_VAL setting via flight mode.

Putting it All Together - Flight modes and FIXED_VAL

Consider a glider with two flight modes. We wish to enable the spoilers in landing mode, so that they can be operate by the stick, but disable them in F3F mode (i.e. hold them always in a fixed position).

Below is the Adjust Controls menu, for the Spoiler control. The shots below show the FIXED_VAL settings for the Landing and F3F modes.


Setting a preset to disable spoiler in F3F mode

 

Trim Offsets are not done using presets!

A bit of a diversion here... suppose your model requires a bit of up elevator trim during the launch phase. Should you program this using FIXED_VAL? Emphatically NO (I've seen some bizarre methods of achieving this trivially simple task!).

To set a trim offset,

  1. Switch the relevant flight mode
  2. Enter the Adjust Control menu
  3. Adjust the elevator's CENTRE attribute.


Trim set to -9% in landing flight mode. This added to the trim lever position, currently centred.

The CENTRE attribute is added to the trim lever position to provide a trim offset specific to the flight mode.

Now, let's see a few genuine examples of presets using FIXED_VAL, and how they can be combined with flight models...

Example flight mode scheme

Let's further explore flight modes, by looking at the setup for a glider. This time, we will consider just three flight modes Launch, Normal, and Landing (we'll drop the Aerobatic mode). Here are some typical preset and trim settings which are easily implemented with flight modes.

 

Flight Phase CONTROLS
Spoiler Flap Elevator
Launch Goal: Disable spoiler

Action: Spoiler control:
FIXED_VAL mode = ON,
FIXED_VAL value = 100 		Goal: Control flaps via lever

Action: Flap control:
FIXED_VAL mode = Off (the default). 		Goal: add some up-trim

Action: Set Elevator CENTRE attribute to suit (this will be added to trim lever position).
Normal As above Goal: fix flaps at zero camber, and deactivate flap lever

Action: Set flap FIXED_VAL
mode=ON,
value = zero 		Goal: Use default elevator trim

Action: set Elevator CENTRE = zero
Landing

Goal: Enable spoiler stick

Action: Spoiler control:
FIXED_VAL mode=Off

 As above As above

Using the Flight Mode switch as a control switch

Flight mode switches are activated by 'secondary' switches, which cannot be used to directly control a servo (well not easily). However as we shall see there is a workaround. Why should this be necessary at all though? The best way to illustrate this is by an example.

Suppose that you have a glider with a tow hook release servo activated by a switch, say 'G'. Suppose also that you have a flight mode switch SO1 to switch between Launch and Normal modes. Typically when launching, you would start in Launch mode (SO1), and lock the tow hook (G). At the top of the line, you'd release the tow hook (G), then revert to Normal mode (SO1). Each phase change requires two switches to be flicked almost in parallel. Wouldn't it be easier if only one switch could be used for both flight mode selection, and tow hook release?

Well, there is a way to do this. Simply assign a FIXED_VAL values for the Tow hook control, for all flight modes. Then the Tow hook servo is then controlled solely by the flight mode switch (even though it is assigned to G).

What Flight Modes Can't Do

Flight modes affect adjustments at the control level, like DIFF, EXPO, FIXED_VAL etc. They cannot be used to select different curves, centres etc. at the servo level - at least not directly. However - you've guessed - there is a workaround for this. I'll leave this for another time.

(I think 'workaround' is not the right term - it suggests that the designer of the 4000 somehow left out a feature. In fact he just provided all the right functions to allow reasonably simple setting up, while allowing you - the user - to use your creativity should you need to.)