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Car RC systems
- how it all works
Just like everything else in the radio control world, car rc systems are advancing very quickly and are better value than ever before.
RC cars and trucks are almost always 2 channel with control to motor and steering, and with the exception of very simple mini rc vehicles, such as the 'Micro Racers', a standard radio control set is fully proportional. This means that your rc car or truck responds directly to how much you move the controls on the transmitter.
In other words, if you move the throttle trigger just a small amount then the motor will only increase slightly; move it all the way and the motor will go to full throttle. And the same with the steering control, if you just move it slightly then the model will only turn slightly.
Basically speaking, having a fully proportional rc system means that you always have complete control of your rc car or truck (in theory...).
Browse a good selection of car rc systems.
Transmitter (abbreviated to 'Tx')
RC car transmitters used to be the traditional 2-stick type and some users still favour this design of Tx. But much more commonplace nowadays is the pistol grip style rc car transmitter with a trigger for throttle control and a wheel for steering control.
Above: a pistol grip and traditional 2 stick rc car transmitter.
The pistol grip transmitter is a great evolution; they're very comfortable to hold and offer precise control of the car. Having said that though, if you've been used to a traditional 2 stick Tx then pistol grips do take a bit of getting used to, simply because they are completely different.
With a pistol grip transmitter the car or truck motor (whether gas or electric) is controlled smoothly by the trigger while the steering is controlled by rotating the wheel of the transmitter. The transmitter can be held in 2 ways, depending on whether you're right or left handed.
Use your index finger on the trigger and your index finger and thumb of the other hand to turn the wheel - you may find that you're more comfortable with it one way than the other, regardless of whether you're right or left handed. It's really just a case of 'suck it and see'!
Above: how to hold a pistol grip Tx; either left hand on wheel and right index finger on trigger (shown left) or vice versa, shown right
NB: While right-handed pistol grip transmitters can and do accommodate many left-handed drivers, only one or two true left-handed pistol grip transmitters (with the wheel on the left side) are currently available and this segment of the market still has significant room for improvement. Some transmitters are reversible, such as Futaba's 3PK range. (This info kindly submitted by Tom Eggert of Lombard, Illinois - thanks Tom!)
Receiver (abbreviated to 'Rx')
In the same way as a traditional radio or television receives a signal from the broadcasting station, a radio control receiver receives the signal that is sent out by the transmitter when any input is made by the operator.
The receiver is located within the model and is directly connected to the servos by 3 small leads per servo; a positive, negative and signal lead. A single wire antenna extends from the circuit board inside the receiver to outside of the model. This antenna should never be cut or looped up to reduce its length; by doing so its ability to receive the signal from the transmitter is drastically reduced, which can result in disastrous consequences by way of the model going out of range too early.
The signals, once received, are passed on to the servos which move in direct response. This whole process of the signals passing from the transmitter to the receiver, then sent through to the servos, is called modulation and can be digital (more common) or analogue (not so common nowadays).
Servos
A servo typically consists of a plastic outer body inside which is a small but powerful electric motor, linked to a set of plastic or metal gears via a feedback potentiometer. These are in turn directly linked to the servo horn, or arm, located on the top (exterior) of the servo body.
This horn is the 'hand' of the servo and links directly to the controllable features of the car or truck i.e. the motor throttle and steering arms. Of course, if the rc car is electric powered then an ESC (electronic speed control) is used to power the motor, in place of a servo. A servo is used for glow plug powered rc car engines though.
One separate servo is needed for each controllable channel and connects to its respective function by straightforward linkages, typically short metal rods.
When the signal from the transmitter is received by the receiver, it then travels through to the servo via the signal lead. The circuitry inside the servo tells the feedback pot and hence motor how much to move and in which direction. This in turn rotates the gears and hence the servo horn and linkage. This final movement of the linkage controls that particular operation of the car, whether it's opening or closing the throttle or turning the front wheels left or right.
Many types of servo are available depending on the usage required; they're available in different sizes and power but a 'standard' servo that will come as part of the radio control set will be fine for using in an rc car or truck.
Crystals
Crystals determine which frequency channel the car rc system will operate on. For most rc surface vehicles a set number of channels have been designated within the 75MHz and 27MHz frequency bands but this range can vary from country to country (see all the North American rc car frequencies).
Both the transmitter and the receiver need their own crystal to operate correctly and they must match frequency exactly. The specific frequency of the crystals determines your channel number or color.
Although you can't change the main frequency band of your car rc system (i.e. from 75MHz to 27MHz), you can change the channel number or color within that band, simply by putting in a different set of crystals. In fact it's always a good idea to carry at least one spare set of crystals with you so that you can change channel at anytime if other drivers are occupying your usual channel. When buying extra crystals, try and choose a range of widely spread channel numbers.
More recently, 2.4GHz car rc systems have come in to use and these operate using a different type of technology. While the fundamental radio signal transmission and reception principle is there, the whole process is different and this newer technology results in a much stronger and interference-free signal. 2.4GHz car rc systems don't require crystals to operate, instead the receiver is 'bound' to the transmitter on a particular frequency channel within the designated 2.4GHz channels.
Browse a good selection of car rc systems.
Batteries (cells)
The most common battery cell size for car rc systems is the AA 'torchlight' size. It's normal for the transmitter to take 6 or 8 cells and the receiver to be powered from 4 cells if it's a glow plug powered car, otherwise the receiver and servos get their power from the motor battery pack in electric powered cars.
Radio control sets don't consume batteries too quickly, and the newer 2.4GHz car rc systems are even more efficient, but obviously with very regular use you do need to be aware of the power level of the batteries. A full day's action is usually enough to drain the overall battery level to a critical one. Low battery levels - even if just one cell is flat - can, and will, result in your car going out of radio range sooner than expected, with the consequent loss of control.
It's a very good idea to buy rechargeable batteries if you can. Nickel Cadmium (NiCD, or 'nicads') and Nickel Metal Hydride (NiMH) cells are commonly used in car rc systems. NiMH cells have greater capacity and performance than NiCD and are now the preferred choice for many drivers.
Rechargeable cells are quite a bit more expensive to buy than disposable (non-rechargeable) ones but they soon pay for themselves. Typical NiMH cells can last for up to 1000 charges if treated well and charged correctly, so that's a lot of rc driving!
Always be very aware of the battery level in your car's rc system. Radio control transmitter battery meters, where used, are quite accurate so you should be able to tell the state of the batteries from that. If in doubt, charge or replace! If your transmitter is a basic one and doesn't have a meter, it would be well worth investing in a small handheld electrical voltmeter to check your battery levels. If the battery level is low then your car will go out of range quickly and you'll lose complete control.
2.4GHz car rc systems
The general information above relates to the standard MHz rc systems but many modern car rc systems now make use of the new 2.4GHz 'spread spectrum' radio technology. The fundamentals are the same but there's a big difference in how the transmitter and receiver communicate with each other.
Essentially, when you turn on the Tx and Rx they scan the designated rc 2.4GHz frequency channels until a free one is found, then they lock or 'bind' together on this channel. A second channel is also locked on to, so if the first one fails for any reason then there is a back-up channel that the system can still operate on. Once bound the channels become secure and impermeable to any interference.
2.4GHz radio systems are becoming more and more common, rapidly replacing the traditional MHz sets. The instant response and secure channel bond between Tx and Rx ensure worry-free driving, with exact and precise control through digital servos.
Browse a good selection of car rc systems.
Related pages
RC car frequencies - designated channels for rc surface vehicles.
RC gear for aircraft - an overview of rc systems for planes.
