Radio Components

Since we are flying radio controlled (RC) airplanes, it is obviously important to discuss the radio components. There is a wide variety of transmitters (Tx) and receivers (Rx) available to the airplane and/or helicopter hobbyist. They can range in cost from a few dollars to a few hundred dollars. It important to understand the technology and know what the different products offer BEFORE you spend tons of money on this equipment.

Before we get into specifics, lets go over some general information about the radio equipment. You generally have two radio components: a transmitter and a receiver. The transmitter is essentially a remote control. It sends information, in one direction - to the receiver. The information being sent is a constant stream of input corresponding to how you move the stick and the position of all the switches. The receiver that you are transmitting to is safely tucked inside the plane. All of your other electronics are plugged into and controlled by the receiver. Its really not much different than those toy remote control cars you had as a kid.

Not all transmitters and receivers can work together. In fact, most of the time you will need a specific receiver to work with your transmitter. Why is this so? Well, firstly, some of them operate on different frequencies. 72 Mhz radios used to be very popular, but they were susceptible to all sorts of interference. 2.4 Ghz radios are more popular today and are less prone to interference. We will be focusing on this type of radio for the rest of the course. Even when the receiver and transmitter are both 2.4 Ghz, you will still need a receiver made specifically for your transmitter. You cannot just mix and match any 2.4 Ghz Tx and Rx. The reason is that manufacturers use proprietary protocols to communicate between devices.

When buying a Tx and Rx, its important to keep in mind the number of channels that you will be using. Almost all transmitters and receivers are capable of at least four channels (4CH). A 4CH Tx will be able to control only the basic flight functions of throttle, pitch, yaw and roll. Depending on what type of airplane you have, you may need more than that. Some planes have retractable gear, flaps, bomb drops and more. I would recommend at least a 6 CH radio to anyone looking to buy their first transmitter.


The receiver (Rx) is the radio component that goes inside of your aircraft. It will be connected to, and controlling, all of your internal components. There will be a series of pins on the side of the receiver. These pins will connect to several 3 pin connectors that come from your servos and your ESC (more on that in a later chapter). The number of connectors available on the receiver is determined by how many channels it supports (a 8 CH receiver will have 8 connectors). The number of these channels that you are able to utilize will be determined by how many channels the transmitter supports.

Before you use your receiver, you will have to "bind" your receiver to your transmitter. The binding process allows the transmitter and receiver to set up their communication link. Once binded, the receiver will only work with one transmitter. How to bind the receiver can vary between manufacturers, but you will commonly use a jumper to start the receiver into bind mode. You will then follow your Tx's instructions to complete the bind.

While the receiver is pretty easy to set up, there are a few things you'll want to pay attention to. For one, you should always make sure the 3 pin connectors are fully inserted into the receiver. You do not want them coming lose during flight, as it could mean losing control of your aircraft. The receiver will also need to be secured to the plane. Hot glue is a popular choice, but I prefer velcro myself. Velcro will hold the receiver onto the plane, but still allow for easy removal. If you have more planes than receivers, this is a must.

Transmitter Layout

There are technically 4 different transmitter layouts, but in the USA we strictly use "Mode 2". Mode 2 transmitters have the configuration that is shown in the picture above. The left analog stick is used for rudder control (yaw) and throttle. The throttle is controlled by moving the stick along the Y axis, while the X axis controls the rudder. The right analog stick controls the elevator and ailerons. The Y axis will move the elevator (pitch), and the X axis will move the ailerons (roll). All controls, except the throttle, will return to center if they are released.

Some times there are switches and knobs on the top of the Tx. These switches and knobs will control auxiliary components, like landing gear or flaps. You will have a switch/knob for every additional channel that your transmitter supports. Keep in mind, however, that your receiver must have the number of channels you wish to use (or more). If the receiver has less channels than desired, you'll still be able to use it... but you won't be able to use some of those extra switches/knobs. I actually tend to fly with an 8CH Tx, but use cheap 6CH receivers since I rarely use more than 6 channels.

When you are flying your plane for the first time, its very likely that you will not experience a level flight. The plane will often try to yaw, pitch or roll on its own. You can adjust these tendencies by adjusting the trim tabs on your transmitter. In the above picture, the trim tabs are the small black sliders shown both below and to the side of the analog stick. The trim settings allow you to alter the "rest position" of your surfaces. As mentioned, you will typically do this in order to correct an undesired movement in the plane.

The trim tabs shown in the picture are known as analog trim tabs. The tabs physically slide from left to right (or up to down) and you can see their position on the controller. The bad thing about analog trim tabs is that if you fly more than one plane it can become very difficult to remember your trim settings when you switch planes. This means you will usually have to redo the trim settings every time you fly a different plane - a very annoying and sometimes difficult act. The alternative to these are digital trim tabs. Unlike analog trims, the digital ones do not physically change position (its more like a button). Instead, your trim setting is displayed on an LCD screen. The drawback is that these are often harder to see and you have to rely more on the audible tones they emit when adjusting them. Digital trims are usually only present on programmable transmitters, and your trim settings will be stored on a per plane basis.

Programmable Transmitters, Dual Rates and Exponential


Most of the crappy bundled transmitters you'll get with "Ready-to-Fly (RTF)" packages will be 4 CH analog transmitters with no programmable capability whatsoever. In general, you will find the bundled transmitters lacking, if they even work at all. When you are ready to jump to a quality programmable transmitter, you will have several new capabilities. One of the biggest advantages will be the fact that you can store settings separately for each plane programmed into the Tx. The number of planes you can program in will typically be 6+, so most of them will accomodate the average flyer.

For each plane, you will have different trim settings, channel assignments, and mixing. All of these things can be set digitally, through the LCD driven menu system. Beyond that, you might be able to reassign the buttons/knobs/switches, change what appears on the display, and adjust some of the finer settings of your controls. Having this all done on a per plane basis is essential, so programmable controllers like this are highly suggested.

Two very important functions often included with programmable remotes are Dual Rates (D/R) and Exponential (expo). The main purpose of these features is to make your airplane easier to control. Its not uncommon for 3D planes and EDF jets to be very sensitive to movement. In fact, flying them without dual rates or exponential can be extremely difficult. Pilots prefer it when light tiny movements on the Tx result in light tiny movements of the plane. When the plane makes heavy movements, even with a light touch, you will need to implement one of these two features.

Dual rates is probably the easiest to explain. Dual rates is set as a percentage from 0-100%, and that percentage determines how much movement is reduced to the control surfaces. 100% would turn dual rates off, while 0% would result in no movement no matter what. Setting D/R to 20% would mean you have now reduced your movement to 20% of the maximum. You can do this on a per surface basis, where you can choose to set your ailerons to something like 50%, while leaving the rudder and elevator untouched. In this case, your elevator and rudder would have a full range of motion. However, since the aileron D/R setting is 50%, moving your aileron stick all the way to the right would only result in 50% of the maximum movement on the plane's aileron. If you moved your aileron stick half way to the right, the plane would only move the aileron 25% of the maximum movement. Settings like this will tame a plane that rolls way too fast, which is pretty common on certain types of planes.

Exponential is a little harder to explain. Exponential is also set as a percentage from 0-100%. In this case, 0% sets expo to off and 100% will produce the greatest effect. What the exponential function will do is soften the lighter movements on the stick so that they move the control surfaces even less, while keeping the larger movements on the stick relatively normal. In other words, if you move your aileron stick 10% to the right, the expo might cause the aileron to only move 1%. Then using those same expo settings, you move your aileron stick 100% to the right, and the aileron moves 100%. The graph above attempts to illustrate this by showing the expo response (curved line) and comparing it to how the controller normally responds without it (the straight line). You can make this curve bigger by increasing the exponential percentage. For most of my EDF aircraft, I find 20%-30% expo to be a good setting.

Just like dual rates, you can set the exponential function on a per surface basis. I typically find myself using it mostly on the ailerons. You may wonder why you would use the expo setting. Personally, I use it because it makes the small responses almost dead. I have the bad habit of rolling a little bit when I use the elevator. My big thumbs aren't very precise. In order to compensate for this a little bit of expo keeps the flight smooth. You can actually mix and match expo and dual rates, so don't be afraid to experiment until you find a mixture that you like.

The Dipole Antenna

I felt it necessary to add this section because I've met very few people who seem to understand how the antenna on the end of their transmitter actually works. Almost all 2.4 Ghz transmitters use a dipole antenna like the one in the above picture. This antenna has a swivel connection near its base that allows you to angle it in practically every direction. No one understands where they should point this antenna. Should they keep it up? Should they keep it down? Should the tip be pointed straight at the plane? Believe it or not, it actually matters quite a bit - most notably when the plane starts getting far away from you.

The first thing I'd like to say is that you should never point the tip of your antenna towards the plane. The transmitter will emit very very little signal from the tip. The same thing applies to the receiver, as it will receive very little signal when the tip is pointed towards you. Believe it or not, almost all of the signal will be received/emitted from the sides of the antenna. Picture this: you've moved the antenna on your transmitter so it is completely straight, and not bent at all on the swivel joint. You then point the top tip of the antenna straight up, towards the sky, so it is perpendicular to the ground. In this position, the radio waves travel from the antenna parallel to the ground. In other words, the radio waves are travelling in front of you, behind you, to the left of you and to the right of you. Notice how I didn't say they were travelling above you or below you. They are barely travelling in that direction at all. Basically, straight up and straight down are a dead spot with the antenna pointed in this direction.

OK, so we know not to point the tip of the antenna at the plane. Where should you angle it then? Well, without getting deep into the science of wireless signals, here is what I would do for both the transmitter and receiver: On the receiver, angle the antenna so that the top of the antenna points either toward the head or the tail. You want the receiver's antenna to be parallel with the plane's fuselage. We will be doing this because dipole antennas work best when the transmitting antenna and the receiving antenna are parallel to one another. Since you will almost always be looking at your plane from the side, positioning the receiver antenna along the fuselage will maximize reception. Some receivers have two antennas and will use the signal on the antenna with the strongest reception. It does not "double your reception", and only provides a form of fault tolerance in case of a weak signal. Due to this, its best to hedge your bets and point one perpendicular to the other. This way, if you've angled your plane in a way that eliminates reception from one antenna, your other antenna will be positioned completely different and much more likely to still be receiving a signal. If both antennas are parallel, they will usually experience an identical reception

As for your transmitter, position it so that it is pointed at a right angle, either pointed to your left or to your right. Just remember to keep your body squared and facing the plane throughout the flight. You may be wondering why you should not have the antenna right-angled and pointed upwards. The signal will still be headed towards the plane, but due to something called "polarity", the signal will not be as strong. To clarify this, I've assumed you've followed my directions regarding the positioning of the receiver's antenna. If so, pointing the Tx's antenna to the left or the right will keep the antennas parallel to one another. This keeps them at the same polarity, and maximizes the quality of your signal.

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Supplemental Videos From the Web

Antennas 101

This is a complete a thorough tutorial on how wireless signals work, and how the position and type of antenna will effect the signal. This is a very long video, but extremely useful for understanding many of the things in this section.

Mode 1 vs Mode 2

Just a note, we use mode 2 here in the USA, so its worth mentioning that the first part of the video doesn't really pertain to us Americans. It is useful to see the difference between mode 1 and mode 2, and its important that you know the difference so you do not buy the wrong transmitter. The mode 2 demonstration gives you a quick run through of how the controls effect the plane.

Connecting the Servos to the Receiver

This video is a great illustration of how the servo wires plug into the receiver, and how the respective channels control the different surface (ailerons, elevators, rudder, throttle).

Dual Rates Explained

This video is a bit dry, but it offers a thorough explanation of Dual rates and how they work. If you could not understand the wall of text that I ended up writing on the subject, this might help you out.

Exponential Explained

This video is a continuation of the previous one, and it moves from dual rates to the exponential function on your transmitter. Exponential is rather complicated to explain, and I think that this video can go a long way in making the subject easier to understand.

Click Here for the Next Section (Mechanical Components)

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