Understanding R/C Equipment

Hobby Hint

Understanding R/C Equipment by Sig Mfg Company

Modern radio control equipment is extremely reliable and easy to use. You don't have to be an electrical engineer to install and operate a radio control system. Radio systems normally come complete, ready to take right out of the box and install in your airplane. All you have to do is plug the connectors together, charge the batteries, and it should work!

A typical R/C system consists of the following four major components:

1) The transmitter is the hand-held control box that the pilot uses to fly the model. It transmits a coded radio signal through the air, in much the same way that a radio or TV station does. The transmitter is powered by a built-in rechargable battery.

2) The receiver in the airplane picks up the transmitted signal, interprets it, and then triggers the actions of the servos.

3) The servos are small electric motors mounted in the airplane that actually move the control surfaces on the model. There is normally one servo for each control surface. The servos take their signal from the receiver and they move in proportion to the stick movement on the transmitter.

4) The battery in the airplane provides power to the receiver and servos. Nickel-cadmium batteries, usually called nicads, are used in most R/C models because they are rechargable.

Your new radio system will probably also include several other accessories such as a plastic servo mounting tray, different sizes and styles of servo control arms, rubber servo mounting grommets, a servo extension cord, and a frequency flag. The instructions included with the radio system will help you identify all of these parts.

Radio Frequencies

One of the first things you must decide when buying a new radio system is to select which "frequency" (channel) you want it to broadcast on. Currently there are 50 frequencies approved by the Federal Communications Commission (FCC) for the exclusive use of R/C model aircraft. These 50 model aircraft frequencies are in the 72 MHz (megahertz) band of the radio spectrum.

FCC Approved Radio Frequencies

For Model Aircraft Use Only

Channel 11 - 72.01 mhz Channel 12 - 72.03 mhz Channel 13 - 72.05 mhz Channel 14 - 72.07 mhz Channel 15 - 72.09 mhz Channel 16 - 72.11 mhz Channel 17 - 72.13 mhz Channel 18 - 72.15 mhz Channel 19 - 72.17 mhz Channel 20 - 72.19 mhz Channel 21 - 72.21 mhz Channel 22 - 72.23 mhz Channel 23 - 72.25 mhz Channel 24 - 72.27 mhz Channel 25 - 72.29 mhz Channel 26 - 72.31 mhz Channel 27 - 72.33 mhz Channel 28 - 72.35 mhz Channel 29 - 72.37 mhz Channel 30 - 72.39 mhz Channel 31 - 72.41 mhz Channel 32 - 72.43 mhz Channel 33 - 72.45 mhz Channel 34 - 72.47 mhz Channel 35 - 72.49 mhz

Channel 36 - 72.51 mhz Channel 37 - 72.53 mhz Channel 38 - 72.55 mhz Channel 39 - 72.57 mhz Channel 40 - 72.59 mhz Channel 41 - 72.61 mhz Channel 42 - 72.63 mhz Channel 43 - 72.65 mhz Channel 44 - 72.67 mhz Channel 45 - 72.69 mhz Channel 46 - 72.71 mhz Channel 47 - 72.73 mhz Channel 48 - 72.75 mhz Channel 49 - 72.77 mhz Channel 50 - 72.79 mhz Channel 51 - 72.81 mhz Channel 52 - 72.83 mhz Channel 53 - 72.85 mhz Channel 54 - 72.87 mhz Channel 55 - 72.89 mhz Channel 56 - 72.91 mhz Channel 57 - 72.93 mhz Channel 58 - 72.95 mhz Channel 59 - 72.97 mhz Channel 60 - 72.99 mhz

Only one R/C model can be flown on a frequency at one time! In order to fly more than one model at a time, they must be on different frequencies! The signals from two transmitters broadcasting on the same frequency would interfere with each other, resulting in a total loss of control and both models crashing.

The R/C system you buy will be pre-tuned to broadcast on only one of these approved frequencies, and unlike a TV set or AM/FM radio, it cannot be quickly switched to another channel simply by turning a dial. In order to change the frequency of an R/C system, it must be sent to a factory authorized repair center for retuning. For this reason, it is important for you to give some serious study to the question of what frequency to select for your new radio. Take time to ask the experienced R/C fliers in your area for their advice on frequencies. They will be able to tell you if there are any frequencies you should avoid locally. Some of the frequencies may be overcrowded with fliers, meaning your flying time will be limited when you go out to the field. There could also be one or two frequencies in your part of the country that suffer from highpowered non-modeling transmitters that operate on nearby frequencies.

FREQUENCY IDENTIFICATON: Most active flying fields use some sort of frequency control system to help avoid interference. Typically, this involves a series of clothes pins, each with a channel number, which requires you to have the correct pin before "switching on:" Also, be sure that your transmitter is equipped with an AMA-approved "frequency flag" to enable other fliers to readily see which channel you are operating on.

The main thing to remember about frequencies is that only one person can transmit on a certain frequency at one time. Before turning on your transmitter at the flying field, it is your responsibility to make certain that no one else is operating on the same frequency.

FREQUENCIES FOR NON-FLYING MODELS: Apart from the above listed model aircraft frequencies in the 72 MHz band, the FCC has allocated 30 frequencies in the 75 MHz band for exclusive use of R/C'ers who build model cars, boats, or any other type of non-flying "surface" vehicle. The FCC differentiates between "aircraft" and "surface" models because of the potential for radio interference between the two distinct classes of R/C models. For instance, an R/C car being operated in someone's driveway could cause an R/C airplane being flown several miles away, out of the car driver's sight, to fly out of control and injure someone, if they were on the same frequency. To avoid possible interference of this kind, "aircraft" and "surface" models are required by law to operate on entirely different frequencies. It is very important that you are aware of this difference and always use an approved frequency in all of your R/C models. It is dangerous, as well as against the law, to use an aircraft radio in a surface model, and vice versa!

FCC APPROVED RADIO FREQUENCIES

For Surface Models

75.41 mhz Channel 61 -Channel 62 - 75.43 mhz Channel 63 - 75.45 mhz Channel 64 - 75.47 mhz Channel 65 - 75.49 mhz Channel 66 - 75.51 mhz Channel 67 - 75.53 mhz Channel 68 - 75.55 mhz Channel 69 - 75.57 mhz Channel 70 - 75.59 mhz Channel 71 - 75.61 mhz Channel 72 - 75.63 mhz Channel 73 - 75.65 mhz Channel 74 - 75.67 mhz Channel 75 - 75.69 mhz

Channel 76 - 75.71 mhz Channel 77 - 75.73 mhz Channel 78 - 75.75 mhz Channel 79 - 75.77 mhz Channel 80 - 75.79 mhz Channel 81 - 75.81 mhz Channel 82 - 75.83 mhz Channel 83 - 75.85 mhz Channel 84 - 75.87 mhz Channel 85 - 75.89 mhz Channel 86 - 75.91 mhz Channel 87 - 75.93 mhz Channel 88 - 75.95 mhz Channel 89 - 75.97 mhz Channel 90 - 75.99 mhz

Additionally, there are six frequencies available in the 27 MHz band that the FCC allows any type of R/C model to use. However, we strongly discourage the use of the 27 mhz frequencies for model aircraft use because of the great probability of radio interference from the thousands of inexpensive, ready-to-use R/C toy cars that are sold on these frequencies.

CHANNEL NUMBERS vs. NUMBER OF CHANNELS The channel number assigned to the frequency shouldn't be confused with the number of "channels", or controls, that your radio can operate on the model. It takes a separate channel to operate each one of the model's controls! For instance, an R/C model that has the same 4 primary controls that a real airplane has would need a 4-channel radio system - one channel to operate the ailerons, one to operate the elevator, one to operate the rudder, and one to operate the throttle. On the other hand, some R/C models, such as the famous SIG KADET SENIOR, are specially designed to fly with only 3-channel control (rudder, elevator, and throttle). Also, many R/C sailplanes fly beautifully on only 2channels (rudder and elevator). Highly advanced R/C scale models will often use the 4 primary channels plus a 5th, 6th, or 7th channel to operate such features as retractable landing gear, flaps, bomb drops, etc.

Generally the channels available on a model airplane radio are utilized as follows:

1 channel radio - rudder control only

2 channel radio - rudder and elevator control, or aileron and elevator control 3 channel radio - rudder, elevator, and motor control

4 channel radio - rudder, elevator, ailerons, and motor control

5-7 channel radio - rudder, elevator, ailerons, and motor control plus options such as retracts, flaps, bombs, etc.

The Sig Kadet Senior and its smaller sister ship, the Kadet Seniorita, are considered by many experts to be the best R/C trainers on the market. They each were designed to use three channels (rudder, elevator, and throttle).

We recommend that your first radio be a 4-channel system! If you are like most people starting in the hobby, you will eventually want to fly models with complete 4-channel controls, even if your trainer only needs 3-channels. With a 4-channel radio you will have the capability to move on to more advanced models after you've learned to fly. You can always use 2 or 3 of the channels to fly simple models, and still have the additional channels available when you want to fly a full house airplane. In the long run it will be cheaper to buy a 4-channel radio right at the start than to get a 2 or 3 channel radio and then try to sell it later when you want to upgrade to a 4-channel model. Not only that, but most 2-3 channel radios come with dry-cell (throw away) batteries, while 4-channel radios normally have rechargeable nicads. That alone is usually worth the difference in price between a 2-3 channel radio system and a 4-channel radio system.

The fabulous SIG SOMETHIN' EXTRA provides incredible performance in a relatively small package. All four primary controls are used to put this ultraresponsive model through any aerobatic maneuver the pilot commands.

Operating the Transmitter

Model aircraft transmitters have become fairly standardized over the years in the layout of the control sticks on the front of the box. It wasn't always that way. In the early days of R/C, many different stick arrangements were tried in an effort to make it easier to fly R/C. Today there are basically three transmitter stick arrangements in use around the world. For a typical 4-channel model airplane, here is how they work:

Mode 1 - Right stick operates the ailerons and throttle. Left stick operates the rudder and elevator.

Mode 2 - Right stick operates the ailerons and elevator. Left stick operates the rudder and throttle.

Mode 3 - Single stick operates the ailerons, elevator, and rudder. Lever on side of transmitter operates the throttle.

Mode 2 is by far the most popular method in the United States! This grouping of the ailerons and elevator on the right stick very closely duplicates the control stick arrangement in a full-size airplane. Consequently, most people feel Mode 2 is a more natural way to fly R/C than either of the other modes. The vast majority of the R/C fliers in the U.S. fly Mode 2, and we advise you to learn that way. All of the radios you look at in the hobby shop will undoubtedly be Mode 2, the other types must be special ordered.

Fore-and-aft movement on the right control stick operates the model's elevator, side-to-side movement of the stick controls the ailerons. In other words, when you pull the right stick towards you, the model will go up. Push the stick forward and the model goes down. Push it to the left and the model will roll left; right and the model rolls right.

The left control stick operates in a similar fashion. Side-to-side movement controls the model's rudder and normally controls the nosewheel or tailwheel for steering the model on the ground. Fore-and-aft movement of the left stick operates the model's throttle. You'll notice that for the ailerons, elevator, and rudder, the control sticks are spring loaded to return to center, while the throttle stick is not. Instead, it has a series of ratchet "clicks" that enables you to set the throttle speed anywhere in its range and it will stay where you put it.

The trim levers work in the same direction as the control sticks, but they only move the servo a slight amount compared to the control stick. This allows you to make small adjustments to the deflection of the control surfaces to "trim" the model to fly hands off straight and level. For example, if the model wants to roll to the left slightly in flight, with no inputs on the controls, simply feed in a bit of right aileron trim until the ship flies level. If it wants to climb slightly when you take your thumb off the stick, trim in a little down elevator by moving the elevator trim lever slightly forward. By carefully adjusting the trim levers, an R/C pilot can make his model fly straight and level all by itself.

The two trim levers are for the elevator (vertical) and the ailerons (horizontal). Notice that both trim levers are in the center or "neutral" position.

FLYING A 3-CHANNEL AIRPLANE WITH A 4-CHANNEL TRANSMITTER: With a typical 4-channel model, the ailerons are the primary control used to turn the model in flight. All turns are initiated by using the ailerons to put the model into a bank and ended by using opposite aileron to get the wings back to level. However, as we explained earlier, some of the best R/C models on the market are designed to fly with only 3-channels (elevator, rudder, and throttle) or even 2-channels (elevator and rudder). In those cases the rudder is the primary control used to turn the model in flight.

If you are going to fly a 2 or 3-channel model airplane with a 4channel radio (very common), it is always best to plug the rudder servo into the receiver slot normally used for the ailerons. This enables the rudder to be controlled by the aileron stick on the transmitter. That way regardless of how many channels your model has, the right stick is always used to make the turns. If your right hand becomes trained to do the turning, it will be very easy to transition between the different types of models without any difficulty.