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
ALL DONE! |
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!
Do you want more on this?
click here to e-mail 'Yes' for more programming examples
STIRLING MARBLEHEAD YACHT RACING CLUB
Inc.
