This is only a preview of the August 1997 issue of Silicon Chip. You can view 34 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Articles in this series:
Items relevant to "A 500 Watt Audio Power Amplifier Module":
Items relevant to "Build A TENS Unit For Pain Relief":
Items relevant to "PC Card For Stepper Motor Control":
Articles in this series:
|
RADIO CONTROL
BY BOB YOUNG
The philosophy of R/C
transmitter programming
This month we will look at some of the
principles involved in the programming of
the modern R/C transmitter. We discuss the
use of memories and initial R/C model setup
for best flying response.
In the course of my radio service
work I spend a lot of time listening to
tales of woe from concerned or frustrated customers, so much so that, like
doctors, you begin to feel that the only
people (or R/C systems) in the world
are those who are unwell.
This can be depressing at times and
it must be a real problem for doctors.
However, in my work as an R/C system
designer, I find these tales very important because I can do something to
help and I have used the information
gathered to great effect in recent years.
The work we did on third-order intermodulation came out of the endless
murmurings and hand wringing that
surfaced in the lead-up to the MAAA
Frequency Subcommittee conference
in Sunbury, Vic. The very popular AM
versus FM articles, which are now being picked up by overseas magazines,
arose from a South Australian reader’s
letter. This poor fellow was under intense pressure from the technocrats in
his club who were telling him to get rid
of his “inferior” AM equipment and
buy the new all-singing, all-dancing
FM gear.
The transmitter intermodulation
articles came to light as a result of
the uncertainties that triggered the
reluctance of the clubs to accept the
earlier issue Keyboards and my subsequent investigations to arrive at the
76 Silicon Chip
truth of the matter. As a result, the
new highly modified Issue 4 Keyboard
has gained wide acceptance amongst
those previously reluctant clubs and
is thus alleviating the worries about
transmitter intermodulation for clubs
across Australia.
Because I was prepared to listen to
the worries, investigate and report on
what I saw as the truth, those SILICON
CHIP articles have completely transformed the way things are being done
in clubs all around Australia. There is
renewed interest in 29MHz operation;
AM no longer carries the stigma imposed by the FM sales hype; 3rd order
intermodulation interference (3OI) is
a thing of the past in most clubs and
transmitter intermodulation is now
well understood.
However, in the words of one
member of the trade, the transmitter
intermodulation articles “created a
storm” and there are now opposing
points of view circulating in the R/C
movement.
Some members of the trade are
not too happy about those articles
because they have shifted the emphasis to dual-conversion receivers for
operation on 36MHz and those in the
trade not supplying dual-conversion
36MHz receivers are walking around
with noses severely out of joint. At the
top of the list of these trade members
is Bob Young of Silvertone Electronics,
who does not yet have a dual-conversion Rx in his range.
This is interesting because it is
being whispered in certain quarters
that Bob Young of SILICON CHIP fame
is pushing the Tx intermodulation
line to help Silvertone sales. Wearing
two hats is a trying process at times.
Programming
Now let’s get onto the main theme of
programming transmitters. There are a
wide range of people engaged in R/C
activities. Some just need a toy to play
with for a few hours to take their mind
off work or home pressures. Others,
like the dedicated international level
contest modeller, need the very best
that technology can provide for that
competitive edge. In the middle is a
vast array of wants and needs.
Sadly, modern mass-production
and marketing techniques tend to
constrain development so that the
needs of the many tend to be forced
along lines dictated by the needs of
the few. Such is the case in modern
transmitter development and now the
beginner and sports flier is faced with
a choice of the computerised monster
more suited for the international competitor or nothing.
It was to bridge this gap that I designed the Mk.22 transmitter which
we have covered in past columns.
Unfortunately, whilst that transmitter
fulfilled the necessary technical role,
the high cost of manufacture in this
country has lifted it out of the beginners’ price bracket.
Having listened and established
that there is much unhappi
n ess
regarding the programming of the
Fig.1: servo error should be minimised by transmitting the
maximum number of steps available and using the mechanical
linkages to reduce the control surface travel. This also stiffens the
linkage in regards to control flutter.
Fig.2: An off-centre servo will give unequal throw about neutral
and will call for less than ideal settings in the transmitter.
modern computer radio, let us see
what can be done to ease some of the
burden. This month we will look at
the fundamental principles of programming transmitters and some of
the common complaints associated
with this programming.
As programming begins with the
model design, we will start from the
very beginning.
Crook manuals
The single most common complaint
that I receive is that the instruction
manuals are almost incomprehensible. Add this to the fact that the
programs are now so complex and it’s
not hard to understand why so many
people are completely overwhelmed
by the whole business. One customer told me that he had flattened the
Tx battery three times just trying to
program exponential control into his
elevators. Another told me that she
had locked out all functions except
basic 4-channel operation.
The poor quality of the factory
manuals has driven several people
to completely rewrite the manuals
for some systems, so have a look at
what is available in the model shops
for your system. There is an excellent
manual written in good English by
Don Edberg for the Futaba Super-7
system, for example. Not only does it
show how to program in easy logical
steps but also gives the theoretical and
practical reasons for using each of the
programming functions.
There is no doubt that the computerised encoder is by far the best method
of encoding and a virtual must for the
serious competitive modeller. However, in trying to make the transmitter
all things for all people, the manufacturers have completely lost the plot
in regard to a simple transmitter for
the beginner and sports flier. So let
us look at some of the fundamentals
in order to simplify programming for
these two groups.
Model memory
One of the very interesting developments in the computer encoder is
that of model memory. This allows
each program to be stored in a separate
memory so that the program may be
recalled when needed.
This has opened new avenues
for the contest flier in that multiple
configurations of a single model may
be stored in separate memories and
changed in flight. Thus, an F3B model
may be configured for towline launch,
cruise, endurance, speed or landing
(crow), all at the touch of a button or
flick of a switch.
This is pretty powerful stuff considering that six to eight servos may be
involved with multiple point mixing
on most of these servos. Programming
such a model takes years of experience
and requires an excellent knowledge
of aerodynamics combined with a very
sound grasp of the ramifications of
swapping between programs.
At the club level, a more mundane
use of model memory is to be found.
This is the process of storing the flight
trims for each model so that when
each model is flown that program is
called up ready for use. This program
may also store such information as
direction of rotation of the servos,
channel allocation, servo travel length
and mixing ratios.
Now it is immediately apparent
that there is great danger here for the
absent-minded or the modeller who
is less than fully aware of the value
of preflight checking.
What if the model is flown with
the wrong program loaded? Controls
may be reversed, mixed incorrectly or
worse still, allocated to different channels. Anyone who has ever taken off
with the ailerons reversed can attest
to what happens next. I have done it
in my early days but God alone would
know how you would cope with a
channel wrongly allocated. Horror
stories abound in all clubs of models
flown with the wrong programs in
place and there is absolutely no excuse, for if the correct preflight checks
had been carried out the error would
have been found on the ground.
I am not a great fan of model memory for this type of application. At
the height of my contest flying career,
long before model memories were
invented, I flew aerobatic, helicopter
and pylon models all from the one
transmitter and on the same day. I
even refused to use “dual rate” because I believed that flying was pure
instinct and to learn to use two sets
of control responses only complicated
the learning process and diminished
the final performance.
I could also have used as many
transmitters as I needed (after all I
did manufacture the things) but again
I wanted that one transmitter to be a
part of me. I wanted no variations in
stick angles, stick movement, spring
pressures, switch placement or
transmitter weight or feel. I wanted
August 1997 77
Radio Control – continued
every hour of practice to reinforce my
familiarity with that one transmitter.
And it worked. I won many a contest
against some of Australia’s best fliers
of those days.
Setting up the model
The secret of my success was all
in the setting up of the model. Now
there are certain fundamentals which
are currently being ignored at club
level due to the fact that computer
transmitters permit sloppy practices
which are not in the best interest of
peak performance of any model.
The techno-junkie will revel in the
flexibility of the computer encoders.
Rudder too sensitive? No problem;
just dial in a 50% reduction in servo
travel. Elevator operating in the re
verse direction? No worries; just flip
it with servo reverse. And that is how
the program stays for the rest of the life
of the model. The next model is set up
just as casually with travel directions
flipped, etc and the stage is set for a
possible calamity.
The astute modeller will look at the
setting-up process from the design of
the model onwards, with a view to
maximising performance, reliability
and safety from the very outset. This
astute modeller will realise that dialling out 50% of the servo travel at
the transmitter end will immediately
double the amplifier minimum impulse and servo gear slop errors at the
servo end, reducing control accuracy
in flight and possibly exposing the
model to control flutter.
Our diligent modeller will instead
aim at minimising servo error by employing the maximum number of steps
available in the transmitter and using
the mechanical linkages to reduce the
control surface travel (see Fig.1). This
also stiffens the linkage in regards to
control flutter.
What our thinking modeller will
do is use the transmitter to quickly
establish the correct control throws
on the field by using the electronic
adjustments and then, when he arrives home, transfer these adjustments
into the mechanical linkages, paying
particular attention to setting all transmitter trim controls to neutral, setting
servo arms to 90° and resetting the
transmitter for maximum data transfer.
78 Silicon Chip
If your model flies with control surfaces and/or servos off centre, badly
balanced controls and more control
throw than is necessary, then it is
not correctly trimmed and you will
never be able to execute manoeuvres
properly. An off-centre servo will
give unequal throw about neutral (see
Fig.2) and again call for less than ideal
settings in the transmitter.
Of course, this can be very useful
for maintaining maximum resolution
in the transmitter under certain conditions but to leave it because of laziness
is wrong. Certainly small variations
can be accommodated without loss
of system integrity but the operative
word is “small”, if you care about top
performance.
Our thinking modeller will also realise that one day he or she is bound to
make a mistake. Thus, he will always
attempt to design each model so that
servo reversing is not necessary, at
least on all flying controls.
Suddenly, our astute modeller
realises that, in the event of the
wrong program being loaded, he has
sidestepped a potential accident as
a result of attention to good practice
and that perhaps he does not need
model memory anyway. Thus, we
have now greatly reduced the number
of programming steps required to set
up any one model.
Certainly this is the case for most
sports fliers and great care should be
exercised in not allowing yourself
to fall into the trap of the quick and
dirty fix. Programming makes it very
easy to slip into sloppy habits. Yes,
it is more tedious and yes it appears
to negate the major advantage of the
computer radio but long term success
is measured largely in the degree of
finesse that one applies to his trade.
Allied to the foregoing is the problem of using dual rate to cut down
on excessive control throw. Again,
the end result is to increase the servo
inaccuracy. The most impressive fliers that I have seen are those that let
the aircraft fly itself, interfering with
the controls only when necessary. Dr
Ralph Godkin showed me this back
in the early 1960s with the most
stunningly impressive display of low
flying I have ever witnessed – and on
reeds (not proportional) to boot.
Most modellers tend to use far too
much control throw with the result
that the flight looks jerky and out of
control. This particularly applies to
beginners and makes learning just
that much more difficult. Instead, the
controls should be adjusted so that
maximum throw is set to give the
desired result. For example, we were
required to complete three rolls in five
seconds in our aerobatic schedule.
In fact I found that I could get away
with three rolls in six seconds without
loss of points, so my maximum aileron
throw was set to give this result. Likewise, full elevator gave the minimum
loop diameter called for and so on.
Sure, square corners in the manoeuvres complicated things a little but
there are aerodynamic ways around
this. As a result of this philosophy
I extracted the maximum accuracy
from the R/C system combined with
the maximum rigidity of the control
surfaces.
Smooth flying
Consequently people always remarked on how smooth my flying
was and how crisp the exits from the
manoeuvre were. The problem arose
when other people wanted to fly my
models. On several occasions, very
experienced aerobatic pilots nearly
crashed my models because the controls were so soft that they did not have
enough control throw to complete the
manoeuvre they had started. I refused
to permit people to fly my models from
that point on.
Beginners need a little more control throw than this be
cause very
soft controls call for the pilot to be
in absolute control of all situations.
Too much control throw will make
the aircraft twitchy and difficult to
control and greatly increase learning
times. Striking the correct balance is
the important point and it is here that
a good instructor is crucial.
Thus the golden rule in programming your transmitter is to always
look well ahead and plan every step
with that one ultimate result fixed
firmly in your mind – that is, to maximise every aspect of the model’s
performance in order to make you
the most competent, impressive to
watch and safety conscious pilot in
your club.
Next month we will look at
the step-by-step details of proSC
gramming.
|