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[rec.models.rc.land] Newbie Guide and FAQ
Section - 8. What are the different kinds of radios?

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There are two ways of looking at this:

The first way of approaching this topic is from the physical characteristics of the 
radio. In this case there are two types of radios. The most common is a 'pistol 
grip' type radio. This is the type that you hold in one hand, kinda like a hand 
gun. On your trigger finger you have a lever that controls the speed: the throttle, 
with the other hand you hold on to a little wheel that controls the direction of 
the car: the steering. These radios mostly come in right hand configuration - you 
hold the radio in your left hand, and steer with the right - left handed radios are 
also available, but there are fewer to chose from. The second type is a 'stick' or 
'paddle' type. This type of radio you generally hold with both hands, and with your 
index finger or thumb you hold on to two levers sticking out of the top. One level 
is the throttle and the other is the steering. The stick type of radio, in car 
racing, is decreasing in popularity in favor of the pistol grip, but there are 
still few around.
There is apparently a single-stick radio out there. This works similarly to a 
joystick. I have never seen one, I am only spreading the rumor ... If anyone has an 
URL to a manufacturer, please send it my way.

The second way of looking at this topic is the type of communication, the radio 
uses. I will, unfortunately, have to use some electronics terminology to be able to 
describe this. The radio transmits a radio signal which is picked up by a receiver 
in the car. So that more than one person would be able to race their car at the 
same time, each radio is assigned a particular frequency - this frequency is 
referred to as the 'carrier frequency'. Out of convenience, each carrier frequency 
is assigned a 'channel number' (see "Legal frequency - channel tables" at the end 
of this document). Almost all radios today can have their channel changed by 
changing a 'crystal' in the radio - this is a small electronic device which 
generates the appropriate carrier frequency. The radios are intentionally 
manufactured to make this relatively easy to do. The receiver must have a matching 
frequency crystal as well. Normally people get multiple crystal sets, so that when 
they get together with friends or for a race there is less likelihood that several 
people will have the same channel. In fact, if you enter into a race they will 
require you to submit three channels that you can race on, and just before your 
race they will tell you which of your three you must use.
There are different methods to generate the carrier frequency, this is called 
'frequency modulation'. There are three types of modulation that you will see when 
shopping for a radio. AM - Amplitude Modulation - is the simplest, least expensive 
method of signal transmission. The next type if FM - Frequency Modulation - which 
has inherently slightly better range and is less susceptible to radio interference. 
The last type is PCM - Pulse-Coded Modulation - which is a type of AM or FM 
modulation, but it has a greater range and resolution. PCM signals are coded in 
such a way that interference is almost nonexistent.
8.1. What is all this stuff on the radio?

When you drive your car, the radio will impress information onto the carrier wave. 
The type of information that is impressed onto the carrier is: going left / right 
and how far to the left / right, go forward / backwards and how fast forward / 
backwards. Unfortunately, each of these functions is also referred to as a 
'channel'. So a radio that can control steering and speed will be a 2-chanel radio. 
These channels are different than the channels for the carrier frequency; it is 
just a confusingly similar label. The receiver in the car then decodes this 
information, and generates appropriate electrical signals for the devices that are 
connected to it: the steering servo and the speed controller. These devices then 
transform those signals into the physical: your car moves! The term 'proportional 
radio', which might pop up while you're shopping, means that as you press more on 
the throttle the car moves proportionally faster; same goes for the steering. This 
is opposed to simple on-off control: the car is either standing still or going full 
blast - most toy R/C cars use on-off radio control. Check 
<http://www.howstuffworks.com/rc-toy3.htm> for a different explanation of the same 
thing, and with pictures. ;)
All of this is quite simplified here. If you want more (technical) detail you can 
look up how a radio works in any electronics communications textbook.

The method used to generate the radio signal (the modulation) is pretty 
standardized. The way to impress the information onto that carrier signal is 
different for each manufacturer. This means that radio made by company A will 
probably not work with a receiver made by company B, even if you have matching 
frequency crystals. The whole set: radio, receiver, and crystal set come as a 
matched set. There are third party manufacturers that make receivers that are 
compatible with first party manufacturers. Check with the manufacturer of your 
equipment before you commit to a purchase!
One thing worthy of note is that crystals (channels) are interchangeable between AM 
and FM radios made by the same manufacturer. However, the radios are built so that 
crystals are not interchangeable between manufacturers - you need to buy crystals 
made for your brand of radio.

There is also something called a 'synthesized frequency module'. This is referred 
to differently by different manufactures, for example: 'spectra module', 
'synthesized transmitter', etc. The idea is rather simple (to the end-user anyway). 
There is an extra piece of electronic built into the radio that will allow you to 
dial in the desired frequency: no more crystals to swap. You can (but do not have 
to) get a receiver with the same thing in it.

Another feature is something called Battery Elimination Circuit - BEC. Normally you 
need a battery pack connected to the speed controller which drives the motor, you 
also need a separate battery pack to power the receiver itself. Most receivers 
today have a BEC, which eliminates the need for the battery pack going to the 
receiver. The receiver gets its power from the motor battery pack. Less weight for 
your car to carry, less run time though; the tradeoff is worth it however.

8.2. Radio interference

There is a whole bunch of stuff that can cause radio interference. How you detect 
it is very simple: your car goes crazy. If interference is a problem for you, go 
through the following list and see if you can eliminate any of these. I tried to 
put suggestions as to what you could do to fix the problem; some of these are 
simple and inexpensive, while some others ...
 - As stated before, from most to least susceptible types of radio transmission: 
AM, FM, PCM. The less susceptible you get, the more it will cost you.
 - Some people experienced a lot of interference when standing close to their car, 
especially with AM radios. This is especially a concern for nitro cars, when 
starting their car up.
 - Some people claim that the 27MHz band is more susceptible than the 75MHz band 
(in the US). The reasoning here is that the 27MHz band has the channels spaced 
further apart, this leaves more room for error. R/C toy manufacturers, who are not 
very concerned about making quality equipment, take advantage of that. 
Unfortunately, you cannot simply change the crystals to the 75MHz band - you would 
need to get a whole new radio.
 - Sparking (arcing) coming from the motor. Get new brushes; clean your motor; 
install noise capacitors on your motor: check the manuals that came with BOTH your 
motor and your ESC on how to do this correctly.
 - Bad (bad = old, defective, or possibly cheap) servos.
 - People standing next to you are using channels that are next (or close) to 
yours. Change your channel.

8.3. Using a 4-channel (or more) radio with a car

Most radios used for R/C cars are 2-channel: direction and speed. There are also 
3-channel radios; the third channel is used for fancy stuff. For example, some 
people wire up lights on their car to the third channel. Higher number of channels 
(up to 8) is intended for aircraft, but can it be used for cars?

This will work, but there are a few things you must keep in mind. Different radios 
are designed for different applications. You might have to use some trial and error 
to figure out which channel you want to use for the throttle and which for the 
steering on your car. Also, multi-channel radios are intended for airplanes and 
other flying R/C models. The throttle for a car radio is spring loaded, but for an 
airplane it is not. This means that on a car radio when you let go of the throttle, 
it will return to the neutral position. On an airplane radio the throttle will 
stay, by design, wherever you had pushed it to. It will require some getting used 
to, but it can be done.

Yes, there are also legal issues as well! You must use the correct frequency for 
your radio. Certain frequencies are reserved for air use only, and some others are 
for ground use only. At the end of this document, see "Legal frequency - channel 
tables", there is a list of legal frequencies for ground vehicles only.
I personally am no lawyer, and as such I am not familiar with all the legal 
subtleties! In North America the government authority responsible for this is the 
FCC - Federal Communication Commission - which controls everything transmitted 
trough the air. They have a web site, and the relevant pages can be found at: 
<http://www.fcc.gov/wtb/prs/radcntrl.html>, and 
<http://www.access.gpo.gov/nara/cfr/waisidx_00/47cfrv5_00.html>. In the UK it is 
The Radiocommunications Agency; here is the best link I have been able to find: 
<http://www.radio.gov.uk/publication/ra_info/ra60.htm>. Good luck!

8.4. Too much information on radios

Someone posted a message asking for plans to build his own radio. This topic is way 
too advanced for the scope of this FAQ. However, Rudie Shepherd provided the 
original poster with some very excellent URLs to sites with this type of 
information. For those truly into way too much information, here are the links:
MicroPro8000 Users <http://mp8000.rcclubs.com/>
Radio Modelisme (in French and English) <http://home.nordnet.fr/~fthobois/>
RCMICRO: Microprocessor based radio control encoder 
<http://www.eagleairaust.com.au/encoder.htm>

Here are a few more links describing how to build your own electronics, or modify 
your electronics. Please note that modifying your equipment will most certainly 
void the warranty on your equipment. :)
The 7 channel hack: <http://www.teamtornado.co.uk/7channel.htm>
PC-to-R/C Interface: <http://www.mh.ttu.ee/risto/rc/electronics/pctorc.htm>
Micron Radio Control: <http://www.micronradiocontrol.fsnet.co.uk/>

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