JR DSX-12 2.4GHz
The very mention of computer radios is often enough to send the uninitiated running for the shadows. If, until now, you’ve shied away from these marvels of modern technology then settle into a comfy chair and I’ll ease you through an introduction, explaining some of the intimidating features and, hopefully, simplifying the programming of your computer transmitter.
A lot of people are initially put off by computer radios, but with so many examples available it’s actually quite easy to find the right one to suit your needs, even if those needs arent anywhere near that of a competitor in the Tournament of Champions or the Jet World Masters. Most low- to mid-range computer transmitters are more than capable of coping with the needs of a club flyer (and then some).
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The Futaba Field Force 6 and 7 (6EX and 7C series), for example, are ideal entry-level computer radios, with menus that are easy to navigate. As well as providing the basics, these systems are also extremely capable of in-depth program mixing (7C in particular) if so desired.
At the other end of the spectrum the current ‘top of the range’ Futaba 14MZ product offers unprecedented functionality, delivered using colour touch screen technology in one of the most user-friendly packages seen so far (though the price tag may not be quite what the average club flyer is prepared to pay!). Ignoring these top end systems for the purposes of this article, let’s have a general look at what computer radios have to offer.
Pulse mode. Most computer transmitters are able to transmit in two distinct pulse modes. Depending on the type of Rx being used theres a choice of either PCM (Pulse Code Modulation) or PPM (Pulse Position Modulation, also known as FM). PPM was initially chosen for use with R/C aeromodelling because the electronics required to decode the signal are extremely simple, leading to small, lightweight receiver / decoder units. However PCM, although more complex, is now the preferred mode as it offers greater flexibility and reliability.
The last couple of years have seen the introduction of the new PCM 2048 G3 system, which promises double the resolution of PCM 1024 and results in real-time response. However, from the experiences of fellow club members who use the system, I’m told youd be hard pressed to notice the difference!
Digital trims. Ever had the frustration of arriving at the flying field to find that all your Tx trim sliders have moved? This and the annoying task of re-trimming every time you change model disappears with a computer Tx, which has the key benefit of digital trim functions. Essentially these are touch-sensitive trim tabs that can be tapped or held in the direction required. The user is often able to program how the trims react to changes of force on the trim tab switches. For instance, when pressing lightly on the trim you get one speed of operation, and when you increase the pressure, the repetition speed and rate may also increase. With most transmitters, the repetition speed and rate of step can be adjusted to meet the requirements for specific models or, indeed, personal preference. In the absence of being able to sense a physical point of reference on the transmitter whilst youre flying, an audible beep helps to reinforce how much input is being entered. The positions of the trims are often also displayed as a ticker marker on the LCD screen.
Servo reverse. This is the first point of call when setting up any new model on a computer radio. Once youve installed the radio and all the servos are located in their desired channel sockets it’s important to make sure that they’re working in the desired directions. This ‘no frills’ function simply allows the user to reverse the operation of each individual servo as necessary.
Dual rate and exponential. These two functions deal with setting the operation rate and operation curve for any three channels (typically), by movement of an appointed or default switch. The need to be able to switch easily between high- and low-rated movements whilst in flight was quickly realised during the development of the earliest proportional radio transmitters, and as that need is fundamentally unchanged, the basic function also remains the same. The real development with Dual Rates in modern computer radios is the ability to define a percentage of movement per channel (often per side of neutral, also), with the settings being saved in the model memory of each individual aircraft.
Exponential is usually activated along with the programmed Dual Rate settings via the relative switch position. On some transmitters its also possible to link on / off control in accordance with the position of a primary stick, such as throttle. A possible situation for this may be the need for more or less control with only slight stick movements at low throttle settings, such as during the landing approach.
On a personal note, for sport, 3D or general fun-fly models, I prefer to set all control surfaces to maximum deflection and employ a -40% exponential curve, or thereabouts. This allows full control at any time but with such a significant dead band I can still fly as if ‘rated’ by limiting the stick movement. This, incidentally, has enabled me to get out of trouble on many occasions without having to worry about the flick of a switch!
Differential. If your model has a tendency to yaw whilst executing an aileron roll, then you need to employ aileron differential. In the good ol’ days this problem was often tackled by mechanically adjusting the control links and horns of the (usually) single servo.
Most models are fitted with two aileron servos these days and the easiest way to solve the problem outlined, is by using the Differential function of a computer Tx, which allows the user to independently adjust the positive and negative deflection angles of each aileron via the two servos. Most screens will show two percentage values each for AIL1 and AIL2, left and right; each value can be highlighted and adjusted +/- to suit your requirements. In some cases its also possible for the user to trim the amount of down aileron deflection in flight using a fascia-mounted rotary dial.
Flaperons. As Ive already mentioned it’s more common, these days, to have a servo for each aileron, primarily due to the extra functionality thus offered, but also due to the relatively low cost of servos. One of the most common functions available to users of computer radios utilising this wing set-up, is flaperon, which allows the ailerons to be programmed so they operate together in the same direction, offering a flap response as well as aileron control.
Usually used for take-off, landing or just slower flight, both ailerons can be raised and lowered simultaneously at the flick of a switch, or dialled in using a rotary knob. Whilst the Flaperon function is active, regular aileron operation is maintained. In most cases left and right deflection angles can be adjusted separately, making it easy to apply differential to the ailerons. The flap throws can be adjusted independently to trim out any adverse rolling when the function is activated, and you can also program in some elevator trim to counter any unwanted pitching.
Ailevators. This function requires the use of two elevator servos connected to individual elevators, which can then operate in unison to control pitch, and differentially to control roll. It’s a useful tool, particularly in 3D or aerobatic aircraft, where it provides aileron control even at low speeds due to the propeller wash that passes over the tail surfaces. In most cases Rx channels 2 and 5 are used; this means that retractable gear [CH5] is possibly sacrificed.
All the combined control deflections (left and right ailerons; left and right elevators) can be adjusted. With most transmitters its also possible to add differential to the ‘rear ailerons’, making this a versatile and highly adjustable function. This system also has the benefit of redundancy – very handy should the aircraft lose primary aileron control.
Snap roll. Many transmitters have a sprung function switch either at the right, left or on both top shoulder positions that can be employed (amongst other uses) to perform a preset snap roll. Early computer transmitters (like the first generation Futaba Field Force 7) often featured a pair of rudimentary slide switches to select up / down and left / right as desired. In the newest generation of computer transmitters, Snap roll (like most other functions) is now completely adjustable, allowing the user to enter the values for elevator, rudder and aileron.
With the advent of more advanced computer radios, the classic trainer function has received an overhaul. This being the case its now possible for the tutor to dedicate the controls that hell be surrendering to the pupil. For example, to familiarise the pupil with the basics of flight during the first few lessons you can allocate him only the primary functions of aileron and elevator whilst you control the throttle, rudder and any other ancillary items.
Shopping for a transmitter today, youd be hard pressed to find one without even the most simple computer system on board. In the words of that famous aviator Howard Hughes: Its the way of the future!
