What is a Radio System?
Radio systems generally come with
a transmitter (the controller), a receiver, and two servos. Servos go inside
the car to control the steering and a mechanical speed control and are
connected to the receiver. Some radio systems are offered with one servo, or
one servo and an electronic speed control (ESC). High-end radios are
sometimes sold with just the transmitter and receiver allowing the racer to
custom purchase the rest of the system for his needs.
Transmitter Basics
When buying your first radio
system, you'll want to be sure the transmitter has the features that are
right for your kind of vehicle.
First, the word channel is used
two different ways when talking about radio control equipment. First, a car
radio is usually a two-channel radio. This means that it controls two
functions on the car. The first function is the is steering and the second
function is throttle (for both forward and reverse travel).
The second way the word "channel"
is used refers to the actual radio frequency (in Megahertz or MHz) which
the radio transmits. There are several frequencies legal to use for R/C and
each one has been assigned a channel number for simplicity. The same way
each TV station transmits on a certain frequency but is referred to by a
channel number.
Frequencies
There are two separate frequency
bands, 27MHz and 75MHz. There are thirty-six total channels (or radio
frequencies): 27MHz (channels 1 through 6); and 75 MHz (channels 61 through 90).
Identical channels (or frequencies) cannot be operated at the same time. In
other words, two radios on channel 68, regardless of radio type or signal
type, cannot use their radios at the same time. Drivers of nitro powered
cars prefer 27 MHz since it is more resistant to noise created by engine
vibration. However, this band is limited to only six different channels. The
75-band offers 30 channels so it is less likely that someone will be on your
channel.
It is possible to change your
radio's frequency by changing the crystals in the transmitter and receiver.
The crystal controls the frequency. Replacement crystals cost anywhere from
12 to 25 dollars according to the brand and signal type. If you race, you
really need at least one set of crystals on a different frequency. Be sure
to use the correct brand crystals or the performance of your radio will
suffer greatly!
Transmitter Features
The following features can be
found on many economically priced radios:
Servo Reversing
In any given radio installation,
control inputs may end up backwards. This may be due to the linkage design
of the car or the individual servo's rotation. For example, when you move
the transmitter wheel to the right, the car's wheels steer left. To remedy
this, transmitters have servo reversing switches. Just flip the switch and
everything will move the right way.
Steering Dual Rate
This function lets you
electronically limit the amount of steering your car will have. At the press
of a button or the throw of a switch you can have two steering rates--full
throw or limited low. Usually the limited throw rate has an adjustment knob
or "pot" for fine tune adjustments. Dual rate is important for on-road cars
because it helps prevent the rear wheels from sliding out (caused by "oversteer,"
a skittish, hard-to-control condition).
Throttle ATV
ATV stands for adjustable travel
volume. This function limits the amount of servo movement needed for brake
and throttle on a nitro-burning car. It eliminates extra stress on the
servo. On an electric car you can use it to limit the amount of power from
the speed control. This is especially nice when learning how to drive or
passing the controls to a less experienced driver.
The following features are
usually found on more advanced radios:
End Point Adjustment
EPA allows each direction of
movement to have different throw. For example, if your car turns more to the
left, turn down the left steering EPA dial until the car turns the same
amount in both directions. Turning down the amount of left steering will not
change the amount of steering to the right. Sometimes, this feature is
called steering "balance."
Exponential
Sometimes called adjustable rate
control, ARC or EXPO. This feature can be used to smooth the car's responses
without changing the overall amount of steering or throttle necessary for
good control. Some cars need a maximum amount of steering at low speed.
However, when that same car is at high speed, steering can become overly
sensitive. Exponential changes the relationship between the wheel and the
steering servo. One way of viewing exponential throw is to call it
soft-center steering. At high speed, you want less steering throw around the
neutral or straight-ahead steering position of the wheel. With exponential
in use, at full steering wheel throw, full steering is achieved. The same
principle applies to throttle trigger and actual throttle response.
Steering Sub-Trim
This is a handy feature that
allows you to quickly and very accurately adjust steering neutral when
running your car for the first time or any time. It works in addition to,
and in the same way as, the regular steering trim knob found on the outside
of the transmitter. It's an great way to keep the external trim knob (or
tab) in its neutral position for full left and right throw potential.
Radio Receivers
The receiver is your vehicle's
brain. This little "black box" is installed in your car. It receives the
transmitter's radio signal with its encoded control inputs right out of thin
air, translates and separates the code and sends commands to the servo(s) or
speed control.
For best reception, receivers
must be mounted as far away from battery and motor wires as is practical.
Not doing this may cause radio interference. Typically, this is the most
common mistake first time racers will make.
Never let your receiver get wet!
If you have a nitro car which ejects fuel residue (most do), or if you run
your gas or electric car where it's a little damp (e.g. wet grass), tuck the
receiver inside a big latex rubber balloon or in a protective cover to keep
it dry
Servos
Servos either make the car steer
or make the mechanical speed control move when you move the controls on your
transmitter. They come in all sizes, speeds, and strengths.
Choosing the right servo depends
on the demands of the car and driver. To get the most response for your
off-road truck you'll want "monster" torque. For a 1/10th-scale, on-road pan
car, you'll want lightning speed. Some drivers find a slower servo helps
them corner with smoother control.
Damaged servos can be easily
repaired with factory replacement parts. So, don't throw them away because
for a few dollars, you may be able to make them as good as new.
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- BATTERY SYSTEMS
