Program like a pro!

Program like a pro!

Bell, Rick

How do you set up dual rates? What is exponential, and why do you need it? How do you set up differential throw? These are just a few of the radio programming questions I often hear at the flying field about today’s programmable computer radios. When I help pilots to program their radios, most are amazed by how simple it is to do, but the icing on the cake comes when they fly their models. Most pilots instantly see the benefits of a programmable radio. For many modelers, programming a computer radio remains a mystery; they think they need a degree in computer programming or training in the “black arts” to work with them. Nothing could be further from the truth! Today’s computer radios are very user-friendly and intuitive. Let’s look at basic programming and how it can make your flying easier and more gratifying.


The first question is usually “Where do I start?” The simple answer is: get intimate with your instruction manual. Grab your favorite beverage, sit in a comfortable chair, and read the manual from cover to cover. Don’t let its length discourage you, as manuals usually include programming details for airplanes, helicopters and sailplanes, and these all have their own parameters. Review the different display modes and key functions on the transmitter face, and become familiar with the diagrams that show the names and locations of the switches and the knobs and buttons that may be new to you. It’s also a good idea to keep the transmitter close at hand; you’ll learn much faster if you find and use each function on the transmitter as you read about it. Most manuals have a “menu” flow chart that shows the functions available and their sequence in the transmitter. Having this menu handy provides a quick way to find the function you want. OK; now that you’ve studied the manual, let’s move on to the functions that are most relevant to a standard, 4-channel, trainer/sport model.

* Naming the program. Before you start to program, make sure that your servos and pushrods have been correctly installed, i.e., the servo arms are all centered, the trims are at neutral, sub-trim (if available, and sometimes referred to as “control centering”) is set to zero, and the control surfaces are neutral. Radio programming can’t make up for a bad base setup.

When I set up a new program for a model, the first thing I do is insert the model’s name. Most computer radios can store several programs for a number of models. It’s very important to name the programs to match your models; if you try to fly your model with the wrong program, chances are, you’ll crash. Before flying, always check the model name on the transmitter’s screen; it could save you a lot of heartache.

* Servo-reversing. Most servo locations are optimized for easy pushrod installation. A pushrod that has a straight run to its control surface will operate more smoothly and without binding. This also puts less strain on the servo and receiver battery and thereby increases their efficiency. After you’ve hooked up the pushrod to the servo and its control surface, check the control-surface movement to make sure that it matches the transmitter-stick movements. Using rudder to illustrate what I mean: move the rudder stick to the left, and the rudder should move likewise. If it doesn’t, access the servo-reversing function, move the cursor to the rudder channel and change the servo’s direction from normal to reverse. Aileron, elevator and throttle are set up in a similar way.

* Servo travel. Endpoint adjustment (EPA), travel adjust and adjustable travel volume (ATV) are among the terms radio manufacturers use, but they all mean the same thing: being able to adjust how much the servo arm moves in each direction. This function is the “master,” and its settings are carried through to all other functions.

Example: say you’re setting aileron throw: you set up the pushrods for the best mechanical advantage, and at 100 percent of servo travel, the ailerons move 1 inch above and below neutral, but you need only 3/4 inch of throw above and below neutral. Reducing the percentage to, say, 75 percent on both sides of neutral will make the aileron move the required 3A inch on both sides. This 75-percent number is now the new 100-percent travel recognized by all of the radio’s other functions. Other channels that have ATV work in the same way. As you can see, ATV offers an easy way to set up the total amount of control throw.

* Dual rates. Just by flicking a switch, you can use dual rates to reduce or increase servo travel to vary control-surface deflection. Most airplane setup instructions include two sets of control throws-high rate and low rate-for aileron, elevator and rudder to increase or decrease sensitivity. Examples of when dual rates are useful are during aggressive aerobatics and during landing approaches when more control throw is needed.

Now, remembering that the ATV sets the maximum servo travel, you could use it (the ATV setting) as the high rate or set a new high rate and then set the low rate at 50 or 60 percent of that. Some radios have only individual dual-rate switches; others allow you to combine rates (aileron and elevator) and assign them to one switch. When setting up dual rates, I find it useful to make the up switch position the high rate and the down position the low rate; this makes it easy to remember which switch position does what.

* Exponential. A lot of modelers misunderstand this function. Exponential (expo) works with dual rates, is usually programmed on the same screen as dual rates and uses the same switches. Expo allows you to tailor the control sticks’ response rate and is usually used to reduce sensitivity in the middle portion of the stick movement. An example of its use would be with a high-speed pylon racer: when it’s flying at high speeds, small control inputs have large effects on the plane’s flight path and make it look very jerky. With expo to soften the stick’s response around neutral, the inputs aren’t as great, and the plane flies more smoothly.

If you decide to use expo, carefully check the radio’s manual on how to set its percentages. Futaba uses minus percentages and JR uses positive percentages- just the opposite to achieve the same result. To get a feel for how expo works, program in a large percentage on, say, elevator, hold partial stick, and switch expo on and off. You’ll see how it affects servo travel.

* Sub-trims. Sometimes, when you install a servo arm, you can’t center it exactly; this is where sub-trim comes in. It allows you to electronically fine-tune your servo centering. If you use sub-trim, do not use it to make excessive adjustments, as it isn’t intended to take the place of proper mechanical trim adjustments. Excessive sub-trim will also create differential throw and make the servo travel greater in one direction than in the other. An unbalanced control response in which your model rolls faster to the left than to the right can result.

* Differential aileron. On some models, downward aileron travel creates more drag than upward travel does. This phenomenon is known as adverse yaw, and it makes the model yaw in a direction that’s the opposite of the aileron input. A right aileron input will bank the model to the right, and yet the nose points to the left-quite unnerving! Aileron differential programming can overcome adverse yaw by reducing the amount of down aileron throw.

To use differential programming, you’ll need to use a servo for each aileron and to plug the servo leads into separate receiver ports; consult your radio’s manual to find the proper ports. After you’ve programmed in a few percentages, test-fly the model, and adjust the percentages until it performs to your liking.

* Mixing. Here’s where a computer radio really shines-mixing! There are many ways to mix functions to reduce your workload. Most radios have two types of mixes: built-in preprogrammed mixes and programmable mixes. Flying wings, for example, can make use of a preprogrammed mix. Instead of using a complicated mechanical setup that requires a sliding tray and associated pushrods, just plug the aileron and elevator servos into the proper receiver ports, activate the eleven function, and the radio does the rest. Other programmed mixes that come to mind are those for flaperons, quad flaps, aileron to rudder, elevator to flap, rudder to aileron and V-tail.

Programmable mixes are among the most useful of computer-radio features, and they are used mostly to eliminate unwanted flight tendencies. Knife-edge flight is one use: you can program elevator and aileron to correct unwanted pitching and rolling tendencies. Computer radios can have anywhere from none to five or more programmable mixes. Inexpensive radios usually have none or just one mix; high-end radios have many mixes for you to play with.


As you can see, programmable computer radios have a lot to offer us-everything from basic setup to advanced flight trimming. Today’s radios can do it all. Though I’ve only scratched the surface here, this information should help you to start to get the most out of your radio. The best advice is to use the radio’s features to understand them and then apply them to your particular need. You’ll be surprised at what the radio can do for you.

Copyright Air Age Publishing Sep 2003

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