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by Bob Aberle
THIS IS MY 10TH installment in this initial phase of the "From the Ground Up" series. I'll be back next month with some frequently-asked questions and in the April issue the emphasis will shift to fueled models under Frank Granelli's expert tutelage.
At the beginning of this series I discussed some of the basic Radio Control (RC) systems as an overall introduction to the model-aircraft hobby. To keep it simple and inexpensive, I selected a basic three-channel transmitter with a single control stick. I use several of these systems for my flying, so please don't worry; I didn't recommend that you buy something that would quickly become obsolete.
As the series progressed I described the Hitec Neon three-channel system, then the electric power system, and then the Aero Craft Pogo as a first-time (Almost Ready-to-Fly) training aircraft.
My student Jay Federman had already done a bit of flying on his own, and he owned a four-channel, dual-stick RC transmitter. When we flew the Pogo for the first time, using a trainer cable, Jay had to hold the Neon transmitter since it was the one broadcasting the signal. The master control was my transmitter (a dual-stick-assembly four-channel unit), which I held as the instructor pilot. back to top
Jay got confused because the throttle lever is on the rear of the case (of the three-channel transmitter) and it operates with a side-to-side motion. He had done some flying using a left-side control stick that moved up for high speed and down for idle speeds.
I recognized this problem right away, and many readers wrote in to "scold" me for having suggested a three-channel RC transmitter to a beginner. Admittedly, as you progress to four-channel ("full house," as we call it: elevator, aileron, rudder, and throttle control), the throttle control will be on the left stick and is operated with an up-and-down motion.
I guess some apologies are in order. Just keep in mind that the three-channel RC system will never become obsolete. It is well suited for my RC sailplanes, parking-lot flyers, and indoor RC.
I'm getting into more advanced RC systems at this time because eventually you will want to, and when you do you will quickly appreciate some of the extra features they can offer. You will also be pleased to know that many of these advanced radios are simple to operate and are comparatively inexpensive. So let's get into it.
A basic RC transmitter, be it a three- or four-channel-function unit, will not be what we call a "computer" or microprocessor-type radio. It will not have a Liquid Crystal Display (LCD) screen that allows you to set the special commands or controls.
Most basic transmitters have servo reversing, and a few might even offer dual rate control on two-channel functions. Servo direction is usually changed with the flip of a tiny switch (unplugging and rotating a cable on the Hitec Neon). Dual rate control cutback is adjusted by rotating a small potentiometer control (dial). These basic radios have a few switches and potentiometers (dials) but no internal computer circuitry and certainly no memory circuits.
An advanced RC transmitter has an internal computer chip that contains a great deal of stored program information in its memory circuits. It can also store your control inputs, allowing you to operate several models from a single transmitter.
You can tell that it is a computer-driven system because it has an LCD screen on the front of the transmitter case. (One exception is the FMA Direct T-80RF, which is just a small step up from a basic unit). The LCD screen displays a variety of parameters; some are basic and preplanned for you, and others you can call up from a menu system that is programmed into the transmitter.
How you access these menus, make changes, and store the new inputs in the memory is what an advanced RC transmitter is all about. Once learned, you will have many more control features available for your use. You can start with an advanced RC transmitter, but use only basic controls until you gain a certain amount of experience.
Before I get into a computer-driven RC transmitter's inner workings, I must mention several more facts. Most modern RC systems broadcast their signal on frequency modulation (FM). Only a few amplitude modulation (AM) radio systems are still on the market, and they are gradually disappearing.
You can't intermix signals with these systems. An FM RC transmitter can't operate an AM RC receiver. Even within the FM category, there are two types of signals that various manufacturers employ. One is called FM deviation on the "low side." Futaba, Hitec RCD, FMA Direct, and GWS make use of this type of signal. There is also FM deviation on the "high side," as exhibited in radios that JR Remote Control and Airtronics manufacture.
Keeping all of this in mind, a Futaba FM RC transmitter can operate a Futaba FM RC receiver and FM RC receivers made by Hitec, FMA Direct, and GWS. A JR FM RC transmitter can operate a JR FM receiver and an Airtronics FM receiver.
Utilizing smart programming techniques, several RC transmitters are able to select "high" or "low" FM deviation. This can be a bonus since one transmitter can be used to operate almost any brand of RC FM receiver on the hobby market, provided it is on the same frequency (RC channel). Later I will mention an even more sophisticated RC transmitter that uses a synthesizer which is capable of dialing up any of the 50 RC channels available for model aircraft.
I hate to get complicated early on, but in FM RC equipment there is one other type known as pulse code modulation (PCM). It is a technique in which a special digital code is added to the FM signal. It provides much greater interference rejection than regular FM, but it is usually only offered on the expensive, top-of-the-line radio systems. These PCM systems also provide a fail-safe feature that adjusts the controls to preset positions and reduces the engine throttle if interference is experienced.
You should also know that each manufacturer uses its own dedicated digital code, so you must stay with one brand for the transmitter and receiver; you can't intermix these units.
Click on photo to view large image with caption
Types of Advanced RC Systems: You have already been introduced to the basic radio. There are also "first step" computer-driven RC transmitters. These entry-level systems offer many extra control features, are relatively easy to use, and are comparatively inexpensive (full systems range from $180 to $250).
Several manufacturers offer a further step into the computer-radio market with systems ranging from $300 to $500. These offer more features than the first-echelon systems but add a certain amount of complexity. For the all-out expert competition-minded pilot, there are top-of-the line radio systems that cost as much as $1,000 and more. That won't be for you for some time yet!
The First-Step Computer-Radio System: All of the popular RC manufacturers—including Airtronics, FMA Direct, Futaba (Hobbico), Hitec RCD/Multiplex, and JR (Horizon Hobby)—have these entry-level computer-radio systems. Some of the big mail-order hobby companies also offer "house radios," but they are generally made by the manufacturers I just listed.
The model numbers of these first-step radios are important for identification purposes. For instance, the Airtronics VG6000 has a new, innovative menu system. I expect to review this radio in Model Aviation in the near future.
The Futaba T6EXA is simple and affordable (roughly $180!), and this is the one I will explain in depth in a moment. Also popular are the Hitec RCD Flash 5 X and Eclipse models and the JR XP662. I have to admit that at this time I have little experience with the new Hitec/Mulitplex systems from Europe.
You do not need to use any of the special features on these first-level computer radios right away. You can turn off or inhibit the extras while you learn to fly your first few RC models.
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