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REMOTE CONTROL
BY BOB YOUNG
Modellers with dedication; Pt.3
This month, we continue the story of John and
examine his involvement in model car racing.
In doing so, we will look at the development
of model car racing technology over the last 20
years or so, to the high-power models of today.
When I first met John, he was
building and driving full-size racing
cars so I guess that the progression to
model racing cars was fairly natural.
As we have seen from last month’s
story, John’s first love seems to be
model railroading and when he takes
on a job he does it with great flair
and energy.
One striking feature of John’s workshop is the sheer volume of model car
equipment hung neatly in racks and
from hooks on the wall. There are
chassis of all types and descriptions
that effectively present a full history
of R/C car technology over the past 20
years. In this story, we will examine
the development of this technology in
some detail but first a little background
on model R/C racing.
The International Federation of
Model Auto Racers (IFMAR) is the
world governing body for R/C racing.
This is divided into various divisions
and John is the president of the One
Eight Scale division. The Pacific region, in turn, is governed by the Far
East Model Car Association (FEMCA).
I will give you one guess who is the
president of this erstwhile body –
right again, our friend John. Under
this umbrella shelters the Australian
Association of R/C Model Car Clubs.
As you can see then, model R/C
racing is well organised and there are
vast numbers of people who race or
enjoy running R/C models of all types.
John’s own collection of wheeled vehicles ranges from model tanks to high
performance race cars, with racing
trucks, electric cars, scale semi-trailers
and mammoth scale racers all thrown
in for good measure.
John’s son Stewart is a world-class
one-eighth scale car driver and the pair
make up what can only be described
as the ultimate dynamic duo. Their
showcases are loaded with trophies
from all over the world and it is interesting to speculate who dragged who
into the business of R/C racing in the
first place. However, I think it has now
settled down to the usual arrangement:
father builds the models and the son
has all the fun driving them.
Talking with Stewart is fascinating
as he explains the technological explosion that has taken place in model
cars, as it has in all fields of human
endeavour. The series of photos in
this article show the progression of
that technology but they do not adequately capture the actual feel of that
development. When you see all of
the bodies lined up side by side, the
first thing that strikes you is just how
complicated the newer vehicles are.
More than that however, the new
models are so substantial in construction, yet weigh in at not much more
than their fore
bears. This is made
possible by exotic new materials such
as glass-filled Nylon, carbon fibre, etc.
Motor size
Photo 1: the first in a line of model race cars. This is fitted with an OS .15 engine
capable of about 0.3 hp. It has a rigid front axle, small tyres, no gearbox, no diff
& a simple centrifugal clutch.
However, the most striking feature,
to me at least, is the size of the motors. Admittedly, the car in photo 1
is only fitted with an OS .15 but in
those days the OS .15 (2.5cc) was only
fractionally smaller than the OS .21
(3.5cc) and externally both motors
looked almost identical. Incidentally,
the figures .15, .21, etc refer to the
November 1994 83
Photo 2: this chassis is quite capable of absorbing the 1.4hp from the K & B .21
motor fitted to it. Here we see a flex chassis fitted with a simple differential,
single disc brake & independent suspension but still fitted with a simple 2-wheel
drive at the rear.
Photo 3: here we see the first of the 4-wheel drive cars from around 1985.
This car is a P.B. X-5 & features such advanced items as a progressive locking
differential & rear wheel roll steering which is adjustable to provide over or
understeering when cornering. It has a 2-speed automatic gearbox & 4-wheel
drive.
swept volume of the motor in cubic
inches. This is the American system
of engine sizing. The English system
uses cubic centimetres (cc) and the
English sizes are given in brackets.
These days, the American system is
the most commonly used.
Compare the size of the motor in
photo 1 (circa 1972) with the size of
that in photo 4 (1994). The 1994 motor is still only a .21 (the maximum
84 Silicon Chip
allowed under the rules) but it looks
substan
tial enough to be a modern
.49 aircraft motor. This increase in
size has come about because of the
requirements for more cooling and
stress containment, due to the very
high RPM these motors are pulling.
Cooling problems
Cooling in model cars has always
been a major problem, particularly
as the original motors were mainly
designed for model aircraft, where
copious quantities of cooling air were
available. Thus, the cooling fins of the
old model aircraft motors were grossly
inadequate for motors intended to
spend their life locked up inside a
plastic body, away from a high-speed
airflow. The original fix was a bolt-on
heatsink and the car in photo 1 shows
a primitive bent aluminium heatsink
of this type.
This type gradually gave way to
the bolt-on finned heatsink which
in turn gave way to the dedicated
replacement cylinder head. This
came with a very substantial extended
heatsink and replaced the original
cylinder head of the model aircraft
motor. While all this was going on,
the motor rework boys were beavering
away at squeezing out every last drop
of horsepower possible.
The result has seen motor power
skyrocket and thus the need for more
and more substantial castings in the
crankcases and more heatsinking
again. Likewise, cylinders, pistons and
conrods have all increased in size. The
results of this development are shown
quite clearly in the series of photos
presented with this article.
For example, the OS .15 (from
memory) had a rating of about 0.3hp
at about 10,000 RPM. These are approximate figures only as none of us
can remember that far back. In those
days, a good .60 would deliver about
1hp at 10,000-12,000 RPM. Compare
this to the motor shown in photo 2
(circa 1980). David Hyde won the
Austra
lian one-eighth scale sports
GT championship with this car. The
motor (K & B .21) gives out 1.4 hp, a
remarkable increase.
Compare this then to the motor
shown in photo 4 and here we are
looking at a Rossi .21 which develops
2.3 to 2.4hp.
The results of this phenomenal increase in power are cars that are capable of 125km/h on a 90-metre straight,
with acceler
ation of 0-100km/h in
under three seconds! Incidentally,
Stewart tells me that from about 1980
onwards, the model car fellows have
been getting good results with the
newer synthetic oils. Oil such as EDL
and WB have been giving excellent
results with mixtures containing as
low as 8% synthetic oil, 2% castor
oil, 20-30% nitromethane and the rest
being methanol.
Photo 4: this car exhibits the rampant technology of today. It has a motor fitted
with a mini-tuned pipe giving out 2.4hp, an automatic gearbox, 4-wheel drive
with changeable overdrive ratios between front & rear wheels, centrifugal
clutches, Sprague clutches in the gearbox, front wheel drive & independent
suspension. It is all made from exotic materials.
Stewart tells me that the castor oil
is to provide the smoke which acts
as a guide for obtaining the correct
running mixture. I suspect however
that the castor oil also provides the
upper cylinder lubricant required for
the extremely high head temperatures
encountered in model engines. Here I
must add my usual warning that these
are not my recommended figures and
that you use synthetics other than
those mentioned above at your own
peril. Personally, I have never had any
luck with synthetic oils, but I have also
never used the above lubricants. I certainly intend to try some of Stewart’s
fuel in the near future and I will keep
you posted on the results.
Chassis development
Returning now to the actual car
chassis, it is obvious that we are now
faced with a very serious problem.
How do you control or absorb this
amount of power, especially into a
chassis as primitive as that shown
in photo 1? A quick look at it reveals
the inadequacies: a rigid front axle,
small tyres, no gearbox, no diff, and a
simple centrifugal clutch which even
then was inadequate and broke on the
second run. There is no way that this
chassis could absorb 2hp or more.
Photo 2 shows a chassis which has
been developed to a large extent. This
chassis is quite capable of absorbing
the 1.4hp from the K & B .21 of that
day. Here we see a flex chassis fitted
with a simple differential, a single
disc brake and independent suspension but still fitted with a simple
2-wheel drive at the rear. John and
Stewart did extensive re-manufactur
ing on this type of car to get the
performance they required. The kit
manufacturers had not yet caught up
with the enthusiasts.
Photo 3 shows a vastly superior
car, circa 1985. Here we see the first
of the 4-wheel drive cars and the kit
manufacturers are starting to close the
gap. This car is a P.B. X-5. Still heavily remanufactured, it nevertheless
represents a quantum leap in chassis
design. The technology in this chassis
is staggering. This car features such advanced items as a progressive locking
differential, rear wheel roll steering
which is adjustable to provide over
or understeering when cornering, a
2-speed automatic gearbox, and the
very useful (some would say essential)
4-wheel drive.
The 4-wheel drive is particularly
clever and features Sprague clutches, or what are commonly known as
one-way bearings. Thus, when the
rear wheels slip or spin, the power
is transferred to the front wheels via
the Sprague clutches. Now we have a
chassis capable of absorbing all of the
power you can cram into it.
By now it is starting to become obvious that tyres are starting to become
an issue, just as in full size motoring.
Space does not allow a detailed examination of this problem, which could
fill a column of its own. Suffice to say
that the real skill of the driver is in
his ability to assess a track and fit the
correct tyres for that day.
This is particularly difficult when
visiting strange tracks where you
only have one or two days prior to the
competition to prepare your car. The
whole business of model car racing is
an intricate and detailed science and
it is easy to see how the enthusiasts
become wrapped up in beating the
problems presented by this very demanding sport.
Photo 4 shows the latest in the line
of development and here we see rampant technology: a motor fitted with
a mini-tuned pipe giving out 2.4hp,
an automatic gearbox, 4-wheel drive
with changeable overdrive ratios
between front and rear wheels, cen
trifugal clutches, Sprague clutches
in the gearbox, front wheel drive
and independent suspension. And
it is all made from exotic materials.
This is virtually a full kit with little
remanufacturing and the overall finish, design and construction of the kit
is immaculate.
So what is left to separate the men
from the boys on the race track if it is
possible now to just walk into a shop
and buy kits such as this? The four
scales featured in these photos tell
part of this story. These are used for
precise balancing of the cars. I am not
going to reveal just how the balance
is correctly set but suffice to say that
the knowledge required to set up a car
correctly is not easily come by.
Finally, a few words about the
radio systems. Stewart uses simple
2-channel radio sets with few bells and
whistles but is very particular about
the brand and even the model number
of the receivers he uses. He runs the
whole radio on 7.2V but finds only
certain receivers will operate satisfactorily on this voltage, hence his choice
of mainly older model receivers.
He is also very fussy about servos
and servo transit times. He feels that
some of the new servos are too fast and
has settled on transit times of about
0.36 seconds as being ideal. He raises
a serious objection to modern servo
savers, stating that they are no longer
powerful enough to handle the torque
from the modern servo and need to be
SC
doctored to do so.
November 1994 85
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