No need to be shy.
Everyone has to start somewhere, and starting out in a field as diverse as model car racing can be daunting.
It's worth getting to grips with all the knowledge though, because it is a rich and rewarding hobby.
Firstly, there are no stupid questions. Nobody will laugh at you for asking about something you don't know, but this introduction will give you a good grounding and a place to start.
So you have, or want, a radio control car.
Quite often, someone will come to us and ask whether they can race their car at the track.
Our default answer is always "yes", because we try and cater for everyone when they are starting out.
But to avoid disapointment, I'll always ask what kind of model car they have.
The reason for asking this question is to guide the potential world champion to the right track, onroad/offroad, and the right class, so that they can drive with their peers.
So the answer, "A Subaru", doesn't give us the right amount of information. That is simply a description of the plastic shell which sits atop the car.
Model radio control cars come in a bewildering variety.
This isn't helped by the fact that the toy industry and the hobby industry, and the clubs,
all seem to talk about things in different ways, using different names.
Starting at the top, and over-simplifying, there are two types of radio contol model cars.
Toy class models are usually relatively cheap, come with radio gear where you cannot change the frequency, and are built with non replacable parts.
If you put a toy class model on the track, you can expect it to last around 30 seconds before breaking beyond econonic repair.
Hobby class models are generally more expensive, come with radio gear where crystals and frequencies can be changed,
or with none at all, allowing you to source your own, and there is a thriving spares industry built up around the kits to keep them going.
- Toy class models
- Hobby class models
Phylum, Class, Order, Family
Back to our example of someone describing their model car as a "Subaru".
What is it we really want to know?
I think it would be difficult if not impossible to create a complete breakdown of all the different types of radio control model car, and attempt to categorise them.
But we can make a start, with the caveat that there will be anomolies, crossovers, and errors.
At a high level, you have onroad cars, and offroad cars.
Onroad cars are designed for flat tarmac, concrete, (or carpet), and cannot be driven offroad.
Offroad cars, could be driven onroad, but are not designed for, and don't work well, in that environment.
These two broad groups are further subdivided into scales, i.e. sizes of the models, where for example,
10th scale is (roughly) a model one tenth the size of its full scale counterpart.
...and types, i.e. what they are representative of, or maybe what they look like.
Further, for racing purposes, we can then subdivide further, into classes, which could be the same as what I have called type, or could be based on an engine, or electric motor size.
No wonder it's confusing!
So here's my attempt to make some sense of it in a single place.
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Electric or fuel
Some cars are electric, and some cars use miniature engines, with a piston, and liquid fuel, just like their bigger cousins.
Electric cars have motors, batteries, and speed controllers.
Electric motors come in a variety of different form factors, but the most common is a 540 size,
which represents the standard physical dimensions of the motor. These are used in the popular on and offroad 10th scale classes.
Larger motors are used in the emerging 8th scale electric scene, and smaller motors in the 18th scale classes.
They are typically refered to by the number of turns of wire they have on each coil in the motor.
So the old stock brushed class was known as 27T stock, refering to 27 turns of wire on the coil, and
stock refering to the fact that the motor timing advance was fixed at 24 degrees.
Brushless motors have a different way of winding the wire resulting in an extra half a turn, so typically, (again, simplified), they
will be denoted by, for example, 17.5, refering to 17 and a half turns of wire on the coil.
for both types of motor, the smaller the number of turns, the more powerful the motor. A 19T is faster,
and draws more electricity, than a 27 Turn. ditto a 6.5 brushless vs a 13.5.
As recently as 5 years ago, the vast majority of electric motors used in radio control cars were brushed.
This refers to the fact that there were physical brushes, pressed onto a commutator, (comm), by springs.
Brushed motors can be sealed can or rebuildable, which is self explanitory really.
Sealed can motors are clamped together, and therefore have no servicable parts. Eventually they wear out,
and you throw them away. They are cheap to buy though, and as you cant tweak them, they have a place in
controlled race formulas.
Rebuildable motors are screwed together, so you can dismantle them, "skim the comm", to make it round
again, and replace the brushes, bearings and bushes.
Over time, the brushes wear down, the comm wears, the springs lose their tension, and performance drops.
In racing, this gave rise to a vast industry of different types of brushes, comm lathes to maintain the
motor internals, comm drops to add to the brushes to lubricate them, different spring weights, and an arcane library of knowledge which you needed to maintain the motors in tip-top condition.
Now most motors are brushless, which means that there is precicely one moving part in the motor. the rotor, aka the bit that goes around.
This, at a stroke, got rid of the industry, knowledge and experience needed to race competetively...
only to replace it with new know how, and computer software.
Brushed motors are controlled quite simply by limiting the amount of current available to the motor.
This could be done with a simple mechanical switch, a slightly more elaborate but still mechanical sliding potentiometer,
or ultimately, with a relatively sophisticated, but still simple, electronic box to contol the current.
The electronic box is called an Electronic Speed Controler, or ESC.
(Mechanical speed controllers can be known as MSCs).
Brushless motors are a little more sophisticated, in that each of the coils needs to be powered in sequence,
and kept in synch with the varying speeds, as well as varying the current required to energise each coil.
The brushless ESCs are sophisticated pieces of electronics with appreciable amounts of computing power.
After Brushless motors had been around for a while, the manufactureres started to ask what else could be done
with the onboard processing power, to differentiate themselves from what other manufacturers were offering.
Generation 2 BL-ESCs were able to set throttle profiles, brake profiles, current limits, and crucially, timing, and store it in the ESC.
Up to now, if you wanted to alter the timing of a motor, you had to physically move the endbell of the motor.
On a brushed motor, this moved the brushes relative to the coils.
On a brushless motor, this moves the sensors relative to the coils.
The effect, (of advancing the timing), is to swap revs and power for efficiency, and current draw. You also swap revs for torque, which means that if you advance the timing too far, (to get the revs and the power you crave), you reduce the torque to the extent that the motor cannot pull out of the corners, and in extreme cases, cannot pull away from a standing start.
The Generation 2 speedos allowed you to set brushless timing in software, on the ESC, without moving the endbell on the motor.
It was then a short step to alter the timing, as the motor was running, so that you had torque to pull away, but then over a certain number of revs, advance the timing some more to increase the power.
The Gen 2 ESCs which did this were relatively crude, but very effective. Suddely, everone needed to upgrade their ESC.
The so called third generation of ESCs, took this concept further, and provided a number of profiles, which set and varied the timing advance according to a number of different conditions.
The best of the new crop of ESCs, provided a computer interface to allow you to program your own profile of dynamic timing into the ESC.
Some manufacturers also allowed software updates, which meant that you didn't need to buy a new ESC every time new ideas surfaced.
...and in 2009, another new innovation. As well as dynamically advancing the timing with the rev profile, the ability to add in a bunch of timing when the throttle had been open for a set period.
By this time, to get the best from your ESC meant you had to have a computer, and you needed to be able to think about what the motor was theoretically doing on each corner of the circuit you were driving.
some drivers think it has all gone a bit far, and are promoting a new class of zero timed ESCs. Either where the ESC doesn't have the capability to dynamically advance the timing, or can be configured to blink a light to show that it currently isn't doing so.
At Adur, we call this class, "Sportsman Stock", and limit the motor type to 17.5 Brushless.
This class is surprisingly close in performance to the "old" 27 turn Brushed class, which everyone used to start with a few years back.
It's all about chemistry
"In the old days", everyone used NiCad batteries. These are made from Nickel and Cadmium. Cadmium is a "heavy metal", and poisonous to most life forms.
For many years, NiCad batteries were the only option in Radio control.
Around 2005, NiMh bateries arived on the Radio control scene. These are Nickel Metal Hydride. In these batteries the Cadmium is replaced with a metal
alloy which is much better at chemically storing Hydrogen, (as a metal hydride), than the cadmium it replaces.
- Lead Acid batteries, don't have good an energy density, and are therefore too heavy to mount in a radio control car.
- Non rechargable batteries, such as alkalines, would be too expensive to replace every race, and in any case, cannot deliver the current needed to run an electric motor at racing speeds.
These alloys are made from a number of different metals, but their key content is a blend of rare earth metals. the blend varies dependent on manufacturer, patents, cost, and a number of other variables.
Hence NiMh batteries can vary in quality quite dramatically.
The overriding advantage of NiMh over NiCad, is the greater energy density. That is, they can store more energy in a given weight and volume.
This is important in Radio control Racing.
At the time, it was hard to strike a balance between power, and duration. With NiCads, you could go fast, but run out of power after four and a
half minutes, (known as "dumping"), or drive steadier, and finish the race at near full speed.
NiMh, almost at a stroke, removed the capacity limitation, raising capacity by a quarter, and within a year of introduction, nearly doubling the
capacity of the batteries we use.
Now the race was on at the battery manufacturers to increase the power delivery of the cells.
While each NiMh cell has a nominal voltage of 1.2V, when you apply a load across the cell and draw current, that voltage "sags" depeding on
how much current you draw.
Over time NiMh cells evolved to reduce the sag and maximise the voltage, and therefore the power delivered to the electric motors.
If you wanted to go fast, you had to keep buying the latest batteries.
Even worse... The NiMh cells wore out! After being used a few times, the voltage sag increased, and the capacity decreased.
If you wanted to keep going as fast as you were going, you had to measure your batteries and replace when performance became unacceptable to you.
Both NiCads and NiMh batteries are made up of 6 individual cells of 1.2 volts each, (making 7.2 volts).
Each cell is different. It has slightly different amounts of chemicals, slightly different resistance, etc.
For Radio Control racing use, the cells were matched into batches of similar cells.
However, over time, over a number of charge/discharge cycles, the cells became unmatched.
The best chargers on the market could balance the cells when charging, or you could discharge the cells to a common balanced point using a
Maintenance of the expensive NiMh cells became a black art.
Then we were saved by the introduction of LiPo.
Lithium Polymer batteries contain no dangerous poisonus heavy metals. They are a fraction of the weight of NiCad and NiMh cells,
and they have again, a higher energy density. Each cell is 3.7 Volts, meaning we can get 7.4 volts from 2 cells, reducing the balancing problem,
and charging is more straightforward, meaning that quality battery chargers can be cheaper.
There are problems though. Overcharging a LiPo battery will irreversibly damage the battery, and in some cases cause the battery to swell up and expand.
In extreme cases, there have been reports of LiPo batteries bursting into flames, which being a chemical fire, is both very hot, and very difficult to put out.
You must charge them with a LiPo specific charger.
Some clubs insist that LiPo batteries are charged in a fireproof bag, known as a LiPo sack.
Along with these disadvantages come a number of benefits.
- LiPos discharge in a linear fashion, meaning that the voltage does not sag (as much as a NiMh) during the course of a race.
- LiPos last much longer than NiMh cells. I have a LiPo now 3 years old, which has at a conservative estimate, been recharged 300+ times, and is still as fresh and powerful as the day I bought it.
- LiPo batteries are much lighter than NiCad/NiMh which has allowed the racing weight of RC Cars to be reduced, decreasing wear and tear, tyre wear etc.
- You can charge them as many times a day as you want. NiCad and NiMh are damaged if re-charged too quickly, too often. Realistically, you only need to buy one, or two batteries now.
- LiPo batteries don't "self discharge" like NiMh and NiCad cells do. At least when they do, it is very slow.
Its a numbers game
So what are the numbers on the batteries?
All batteries are defined by their numbers. In radio control, the main number you will see, by which batteries are marketted is the mah rating.
Yes. mah = milli amp hours... or the number of milliamps of power, which the battery could (theoretically) deliver over the course of a 60 minute discharge.
You can think of this number as the size of the fuel tank in a real car.
For example, a 3000mah battery can theoretically deliver 3000 milliamps, (aka 3 Amps) continuously for an hour. Or 6 Amps for 30 minutes, or 12 Amps for 15 minutes.
The mah number therefore describes how long the battery will last, but not how much power it can provide to make a motor go faster.
For LiPo batteries, this is provided by the C number. the C number is a discharge rating for the battery related to the capacity.
Typical LiPo batteries will have a C rating of 20, 25 or 30, although I have seen batteries with a C rating as high as 50.
Multiplying the C number by the capacity, gives you a theoretical number of Amps which the battery can provide when current is drawn.
For example, a 5000mah 20C LiPo battery can provide 5000*20 = 100,000 milliamps, (divide by 1000 to get Amps) = 100 Amps.
I'll leave it to you to figure out whether your motor can draw that much current, and whether you need more, (expensive), or could settle for less, (cheaper).
NiCad and NiMh batteries never had a C rating. The assumption was that there was no effective limit on how much power could be drawn,
whereas the chemistry of LiPo batteries does provide a limit, which needed to be communicated, and is now used for differentiation and marketing.
There are other numbers sometimes provided with NiMh and NiCad cells though. Especially on "Race Packs".
these relate to the matching of the cells. How closely the 6 cells in the pack are matched, the capacity as measured under a controlled discharge,
and the internal resistance, as measured differently by every battery matching company.
At best these numbers allowed you to chose between packs from the same matcher at the time of purchase .
At worst, the numbers meant nothing, and could not be compared between different sellers, and in any case, the batteries changed from the very first time you used them.
Dos and Don'ts
- Charge LiPos with a charger specifically for LiPo batteries.
- Charge LiPos in a LiPo sack if the rules of the club ask you to.
- Balance charge your LiPo battery if it has been left standing for more than a couple of months.
- Store your LiPo batteries at circa 2/3 full charge.
- Store your NiMh cells at approx 80% full charge.
- Charge you LiPo and NiMh cells at a maximum of 1C. (This means 1 times the amperage of the capacity. e.g. a 3300mah battery should be charged at a maximum of 3.3 Amps.)
- Dispose of your old batteries sensibly.
- LiPo batteries should be discharged to zero by connecting a light bulb across the terminals. then they can be put in normal household rubish. Some recycling centers can recycle LiPo batteries.
- NiMh batteries should not go to landfill, but should go to a recycling center for reclamation of the rare earth metals.
- NiCad cells should NEVER go to landfill. They are poison, and must be reycled.
- Discharge LiPo batteries below 3V per cell, (i.e. 6V for a 7.4V racing pack).
- Discharge NiMh batteries below 1V per cell. They will never be the same again.
- Overcharge LiPo batteries.
- Forget to change your charger settings, and charge LiPo batteries on a NiMh profile.
- Charge NiMh batteries on a NiCad fast charger, the peak detect is different, and the NiMh cells will overcharge, overheat, and explode, (quietly, by "venting", or noisily, like a firework)
Internal Combustion engines.
In contrast to electric, IC, (Internal combustion), cars, are extremely simple to run.
There are of course nuances to this simple view of the world.
- Select and buy your engine
- Fit it to the model
- Fill tank with fuel
The engines need to be run in, or broken in as some call it, and has to be tuned to suit the atmospheric conditions on the day.
Tuning can be achieved in a number of ways, and there are many help guides around, so I'll not go into depth here,
but it can be as simple as turning one screw the right way.
The engines come in different sizes or capacities, just like full size ones, but it can be confusing,
because the sizes are in cubic inches, American style, rather than the cc or cubic centimeter we are used to.
So a "12", is an engine of 0.12 Cubic Inch capacity, which translates to 2.1cc.
A "21"is an engine of 0.21 Cubic Inch capacity, which translates to approx. 3.5cc.
Fuel comes in different percentages, refering to the amount or blend of oil and methanol in the mixture.
For racing, engine size, and fuel allowed are defined in the rules for each class, which makes things much simpler.
Pick a race class, and then chose your engine and fuel to suit.
crystals, whats allowed. 40 vs 27. AM vs FM 2.4Ghz
- BRCA beginners
- Adur 101s.