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Using a Programmable Radio Transmitter for RC Yachting - by Ben Morris

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Why chose and use a programmable radio?  I have already outlined in Radio Selection why the 2.4 GHz radio systems are really the way to go.  I now suggest that the programming functions of anything other than the very cheapest of the sets are so advantageous that I would not contemplate buying anything less.  These sets such as spectrum DX6i etc are quite reasonably priced.  Almost all of the common radio manufacturers have equivalent radios with similar functionality.

What can be done with the programming functions that make them indispensible?

Consider initially just the rudder servo.  In Rudder Servo Setup I explained how even with the best setup procedure, it is almost impossible with a simple servo to arrange the servo arm to be exactly at right angles to the servo body when the radio is set up with the trim set to the middle position.  The splines on the output shaft are just too coarse!  Sure you can adjust the trim permanently one way or the other but this is just bad practise.  The trim should always be set to the middle as the default position so you know that returning the trim to the middle will always return the rudder to the middle.  To make this adjustment, the computer radio has a programming function which alters the centre trim internally while leaving the manual trim as it should be in the middle!

Other really important features I will deal with later are functions like,

  • being able to store a set of adjustments for different yachts. How many of us have more than one RC yacht?

  • being able to adjust end points for controlling the sail winch

  • being able to make the sail winch move in smaller increments near the in position to allow for smaller more accurate adjustments

  • making the rudder turn less distance about its centre for a given movement of the transmitter stick to allow for more accurate and less drag inducing movements of the rudder (called 'differential' in most manuals)

Different radios have different ways of accessing their internal adjustments and I cannot hope to show each one but instead will indicate how it is done with a Spectrum brand.  Other brands will be quite similar and with a little reading of the manual and experimenting with the controls they are readily learned.

Consider a Spectrum DX6i as probably one of the most common 2.4 gHz radio sets in use by radio sailors.  The set needed is configured in 'mode' 2.  This means that the throttle control which we use for the sail winch is on the left stick and the aileron on the right which we use for the rudder (unless you are left handed and would prefer to use your left hand for steering in which case its a mode one set for you.)  The instructions for programming are the same for either mode.  I will outline the steps to program some differential into our rudder (sets aileron) control


The computer in the DX6i is accessed using the three way roller switch on the right of the display screen.

The switch is activated by pressing on the roller but be careful when doing this that the roller does not turn.  This switch action is used to select the highlighted function or to make a variable value ready for editing or to accept and save a value entered into the program for a particular function

The roller can be turned to the right or left and this has two actions as well.  It is used to move the highlight around the displayed functions.  Rolling it to the right takes the highlight up the displayed list of functions while rolling to the left moves the highlight down the list.  As well once a variable value has been made ready for editing rolling to the right will increase its value to the left will reduce its value

While we may not use many (or none) of the switches on the radio, its a good idea to develop the habit of setting all switches to their '0' position.  This way you know where they are and if you start using one of the switches later you already know where they will be by default.



Normal main screen  Make sure all switches on the body of the radio are in the '0' position



Press roller to display 'Adjust List' screen



Roll roller to left to shift highlight to 'D/R & Expo' item



Press roller to display D/R & Expo screen.  Exponential setting is currently INH (inhibited)



Use roller (right) to shift highlight to the aileron row and the exponential setting



Press the roller to activate the editing of the exponential setting



Use the roller (right) to increase the exponential value to say +25%



Click on the roller to save this setting




Use the roller (left) to move the highlight back to the 'List' position



Press the roller to return to the "adjust List' screen highlight will be on D/R&Expo


Use the roller (left) to move the highlight back to the 'Main' heading


Press the roller to return to the default main screen



Congratulations you have just programmed 25% exponential on the aileron (our rudder) into the computer.  Note that this setting applies only to the set when the 'AIL D/R' (aileron dual rates) button on the radio is in the '0' position.  Test this setting on the yacht now and you should notice that the movement in the centre of the rudder stick makes a significantly smaller movement of the rudder but the total movement at the extremes is the same.  This smaller rudder movement near the centre of the stick movement can be very useful in avoiding overuse of the rudder and allows more control particularly when running in strong winds where too much rudder motion can be only too easy to do.  Click the 'AIR D/R' switch to the '1' position and the exponential is removed.  You should be able to see the difference.  Exponential on the rudder can be increased to 100% if you wish but this means nothing happens to the rudder in the middle of the stick movement then all of a sudden it moves.  Sensible values range between 20% up to say 60%.  Try setting the the position '1' of the AIR D/R to a higher value.  Simply repeat the above process with the switch in the '1' position and setting the value to say 50%.  Then you can select how much exponential to use by using the 0 or the 1 position on this switch at any time.

Now wasn't that fun!



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