Radio control functions
- understanding your TX.
To really get the most out of your new hobby, you need to understand at least the most common radio control functions and features that your new rc system is capable of.
I say 'at least the most common', because most modern rc transmitters are packed with features that you will likely never use!
The absolute fundamental purpose of your rc system is, of course, to control the directional movement of your aircraft, with auxiliary functions being controlled in a secondary manner.
Incidentally, if you don't already know, each controllable function of a radio controlled model is referred to as a 'channel' i.e. a single channel rc aircraft will have control to just one function, whilst a six channel aircraft will have six controllable functions.
RC transmitter types.
There are essentially two basic categories of radio control systems - surface radios for use with rc cars, boats and other land-based vehicles, and air radios for aircraft.
These days, it's common for a two-channel surface radio to be of the 'pistol grip' design, but two-channel traditional 'stick' transmitters can also be bought and these can be used for simpler rc aircraft, notably gliders.
A multi-channel air radio features two sticks and additional switches, but the big difference between stick transmitters of two or 4+ channels is how the sticks move, as illustrated in the following picture...
Above: Stick movements of a traditional 2-channel (left) & 4-channel (right) transmitter.
On a 2-channel stick transmitter in use with an rc glider, for example, the right hand stick moves from left to right, with a natural centre i.e. the stick is sprung.
To correspond naturally with the control of the glider, this stick moves the rudder, or perhaps ailerons instead; either way, this stick controls the left/right directional control of the glider. Moving the stick left will steer the glider to the left, and vice versa.
The left hand stick, also sprung, moves up and down and corresponds naturally with the elevator, although in this case up does not mean up; moving the stick upwards (i.e. away from you) will cause the elevator to drop which will result in a dive, whilst moving the stick down (i.e. towards you) will raise the elevator and cause the glider to climb.
The radio control functions of a multi-channel transmitter (shown above, right) become more complicated because each stick moves up and down and left and right. The right hand stick will, for example (*see below), control elevator (up/down) and aileron (left/right) whilst the left hand stick will control throttle (up/down) and rudder (left/right).
Learning to control two actions with one stick may sound complicated but is mastered with practice and will soon become second nature, much like the way you move your feet when driving a car.
*NB: Various modes are used with multi-channel rc systems, determining which sticks operate which controls:
- Mode 1: rudder and elevator are controlled by the left stick, throttle and ailerons by the right.
- Mode 2: ailerons and elevator are controlled by the right stick, rudder and throttle by the left.
- Mode 3: ailerons and elevator are controlled by the left stick, rudder and throttle by the right.
- Mode 4: throttle and ailerons are controlled by the left stick, rudder and elevator by the right.
See RC transmitter modes in detail.
But which transmitter mode is right for you?
Well, if you learn to fly rc planes at a club then the choice will more than likely be made for you, by your instructor and the airplane you are learning on. By far the most common mode nowadays is Mode 2, and the majority of Ready To Fly rc planes are sold with a M2 transmitter, with Mode 1 being the second option. Modes 3 and 4 are not widely used.
There are pros and cons to the different modes, and no mode is wrong or right; having the ailerons and elevator on the same stick (Mode 2) puts both primary controls in one place and correspond to a real airplane's joystick (although this isn't particularly relevant to rc flying), whilst having the two primary controls on separate sticks (Mode 1) means there's less chance of you inadvertently changing one input while moving the other.
Whichever mode you end up flying with, the chances are that you'll stay with that one for all your flying days. Once you've learned one mode, it's very difficult to start flying on another!
Browse rc systems, if you're looking to buy.
Common radio control functions.
Aside from the main stick controls, additional channels are found on toggle switches and/or rotating dials and sliders, all of which can be located on the face or top of the transmitter within easy fingertip reach (the photo shows the top left corner of a transmitter with many extra channels). These extra channels can be utilised to control, for example, flaps and retractable landing gear, and functions such as dual rates will commonly be operated by such switches.
All channels over and above the four primary ones are called auxiliary channels.
The more common radio control functions and features found on modern rc transmitters include...
- Dual rates - these enable the control surface deflection limits to be changed, while still retaining full stick movement. So you could have 'normal' deflection, plus a setting for decreased and/or increased deflection limits at full stick movement.
Dual rates can be found on some RTF rc airplanes these days, and may be described as 'Beginner Mode' (less deflection) and 'Advanced Mode' (more deflection). These are typically pre-programmed deflection rates, but that varies depending on which radio is supplied in the box.
- Servo reverse - allows the direction of servo movement to be fully reversed, ideal for times when a servo can only be installed in the aircraft in a way which isn't conducive to the required direction of movement.
- Control surface mixing - this is only possible on a computer-based transmitter, which are now commonplace. A single pair of control surfaces is made to act as two separate pairs would. A common example of control surface mixing is to combine elevator and aileron deflection in to 'elevons', on a flying wing type rc aircraft. In this case, the transmitter is operated normally but the single pair of control surfaces combine the two different deflections in accordance with the TX stick movements and so move together, as elevators do, and individually as ailerons do.
Other similar control surface mixing includes flaperons (mixing aileron & flap deflection) and ruddervators (mixing rudder and elevator deflection on 'V' tail aircraft).
- Channel mixing - this is when two separate channels are made to operate in conjunction with one another. For example, you could program an aileron and rudder mix whereby the rudder automatically moves a set amount when the ailerons are deflected. Or you could have elevators automatically drop when flaps are activated.
- Expo - short for exponential, this lets you adjust the sensitivity of the control surface deflection around smaller TX stick movements. So, for example, you can set your elevators to barely move at all when you move the stick around its central position, but then go to full deflection when the stick is moved to its limit. Conversely, but much less commonly, you can go the other way so the control surface moves a lot around the stick's central positions. Expo essentially calms down an airplane that might otherwise be twitchy and over-sensitive to control inputs.
- Travel Adjust - also called End Point Adjustment, and a few other names. This lets you set the travel limits of each servo, normally as a percentage of the servo's normal travel. The upper limit is typically 125% or so. Travel Adjust can be used to set or fine-tune control surface deflection limits, after all mechanical adjustment has been done.
- Sub-trim - this sets the neutral point of each servo, and is handy if you can't get a control surface perfectly neutral with mechanical adjustment (on the linkages).
- Programmable mixes - on today's modern computer radios, almost anything is possible with a bit of programming, or 'dialling in'. Programming menus on such radios are very extensive, and they let you get the most out of your airplane or helicopter. When you're starting out, you won't need to worry about all of the options available to you, but as you gain experience and move on to more complex rc aircraft, so those programming options will come in to play. Some radios are friendlier than other when it comes to programmable mixes!
- Multi-model memory - this means that multiple aircraft can be used with just the one transmitter. Once the particular settings for an aircraft are programmed into the TX (eg trim settings), they can be stored along with other settings for that aircraft, and this can be done many times over, depending on your radio. More advanced radios utilise SD cards these days, meaning a practically unlimited number of aircraft settings can be stored!
Multi-model memory is very convenient, it prevents you having to start setting up from scratch every time you fly a different aircraft with the same transmitter.
- Training function - this allows the student's transmitter to connect to the instructor's transmitter via a cable, or perhaps wirelessly, in a system called a 'buddy box' system. It allows the student pilot to have full control of the airplane, yet allows the instructor to resume immediate control at the flick of a switch, if the student gets in to difficulties.
Browse rc systems, if you're looking to buy.
Radio control trimming function.
All rc transmitters, with the exception of the cheapest toy ones, have a function that allows you to 'trim' your aircraft while it is being flown.
Small trim sliders or buttons, also simply called trims, are located adjacent to each stick, one for each direction in which the stick moves. The trims can be analogue (as pictured right), in which case they are held in place with a simple ratchet system, or, more commonly, digital in which case they are small buttons.
Each trim has exactly the same effect as its parent stick, only to a much finer degree; essentially the trims fine tune the servo deflection of the aircraft and they are used to smooth out any unwanted tendencies of the aircraft in the air. The aim of trimming is to get your airplane flying as straight and level as possible with the main transmitter sticks in their central positions, and with no input from you.
It's quite normal to have to adjust the trims throughout each flying session, as outside factors can affect the aircraft's flight characteristics. But once the trims have been set, they can be left alone until the natural flight path of the aircraft changes and they have to be adjusted again.
Read more about trimming your rc airplane.
When talking about channels, there are 2 different meanings in the radio control world; the number of channels an rc system has, as mentioned earlier up the page, and the frequency channel that the system operates on.
Because all radio control systems send out radio signals, just as a normal radio or TV broadcasting station does, various frequency channels are needed so that more than one rc system can be operated at the same time. So, in most parts of the world, certain channels have been designated, by law, for radio control models and must be adhered to for safety reasons. RC aircraft have their own set of channels while rc surface vehicles have theirs.
For more detailed information on this very important aspect of radio control, see the rc airplane frequencies page.
But with the above in mind, frequency channel control only applies to MHz radio control systems; the newer - and now commonplace - 2.4GHz systems use a different technology, and so frequency channel designation does not apply to them.
A further point to remember when referring to radio frequencies used for models is the modulation. The word modulation refers to the whole process of the radio signal being sent out by the transmitter, received by the receiver and passed on to the servos.
The two standard types of modulation are AM (Amplitude Modulation) and FM (Frequency Modulation), the latter being sub-divided into PPM (Pulse Position Modulation) and PCM (Pulse Code Modulation).
In a nutshell, PCM is the modern digital successor to PPM and does a far better job of guarding against unwanted interference. FM is the most commonly used by nearly all rc aircraft pilots*, while AM is often used on 2 channel surface vehicles and rc toys.
*NB: while the traditional FM MHz rc systems are still in use, the newer 2.4GHz spread spectrum systems are quickly replacing them. Such systems use a completely different frequency band and technology, and it's only a matter of time before the MHz rc systems go the way of the dodo.
Whichever rc system you have, understanding the radio control functions and features on it is very important, to get the most out of it. As with all things in life, it's not necessary to buy the all-singing, all-dancing, most expensive set you can lay your hands on, but do be satisfied that your system will be able to control your aircraft in all the ways that you need!
When you do buy a more advanced radio control system, take the time to get to know it, and your hobby will be that much more rewarding.
Shopping for an RC system?
If you're in the market for a radio control system then buy the best you can comfortably afford. If you buy cheap, you pay the price later on down the line, when it fails on you.
RC manufacturers I can recommend include Spektrum, JR, Futaba, HiTech, FrSky, Multiplex, Graupner, to name a few (in no particular order). Amazon is a good as place as any to buy from these days, follow the product suggestions below to go there...
Radio control gear.
RC airplane controls.
More popular RC Airplane World articles:
Your Instructor: Roger McClurg (maguro on RC Groups)
By now you should have charged your transmitter battery, calibrated the battery voltage reading on the Taranis, and performed stick calibration. You should also have read the Taranis Quick Start Guide (QSG) and know how to navigate the Taranis menu system. You don’t need to know what everything does at this point, you just need to know how to move around in the menu structure. It wouldn’t hurt for you to learn to use those two button press short cuts as well. They can save a lot of button pressing.
The goal for this lesson is to develop an understanding of the main Radio Setup menu, and to provide detailed descriptions of all items in it. A follow on lesson will walk you through all the remaining screens in Radio Setup group.
To complete this lesson, you should:
- Have a charged battery in your Transmitter
- Have OpenTX flashed to your Transmitter with OpenTX version 2.0x
- Read the Taranis Quick Start Guide and understand basic menu navigation.
Settings made in the Radio Setup menus are global, that is they remain the same for every model selected. Certain radio settings such as whether to use the internal or external module are model specific, so they are done in the Model Setup menu for each model. This lesson covers what you need to know to configure the Transmitter‘s global parameters.
OK, if you are ready to go, it’s time to adjust the rest of the radio settings prior to setting up your first model. Grab your Taranis, and let’s get stated.
For a copy of this lesson, click Radio_Setup_Checklist
Menu navigation is performed by pressing the menu keys. Some actions require a long press (LP) of the menu key others a short press (SP) of a menu key. In this and the lessons that follow menu key actions will be in the form of LP or SP and the key name(MENU, PAGE, EXIT, “+”, “-”, or ENT.
- Turn on your transmitter and clear any warning screens.
- When you get to the main model screen, LPMENU to move to the Radio Setup.
- Radio Setup consists of 8 pages of entries. Press “-”to move down through the the entries one at a time. Pressing “+” moves up through the entries. Pressing “+” at the top of page 1/8 (one of eight) will take you to the bottom of page 8. Pressing “-”at the bottom of page 8 will take you to the top of page 1.
- The image below is a combination of all 8 screens. Take the time to move up and down within Radio Setup to get the feel of navigating a multipage screen.
- Go to the top of Radio Setup to Date. Press ENT to begin editing. Pressing the “+” and “-” keys will increase and decrease the year. Once the year is set, press ENT to finish entering the year then press “-” to move to the month. Press ENT to edit the month. Pressing the “+” and “-” keys will increase and decrease the month. Once the month is correct, press ENT then “-” again to finish editing month and move to day. Press ENT to edit the day. Set the day in the same manner you set the year and month. When you are finished press ENT then “-” to move to the hour of the day.
- Time on the Taranis is kept in 24 hour time (sometimes called “military time”). For those of you who are unused to 24 hour time. Just remember 1 through 12 PM are entered as 13 through 24. Just add 12 to the PM time, and you have the hour. Now enter the time in the same way you entered the date. Press ENT to begin editing, press “+” and “-” to increase or decrease the entry, and press ENT again to finish editing. Press “-” to move to the next entry down the list. When you are finished entering the time, press “-” to move down to Battery meter range.
- Battery meter range is used to set the low and high ends of the range of the graphical radio (transmitter) battery meter on the main screens. This setting only affects the battery meter display. Set the first number to the voltage where you consider your transmitter battery “empty” the second number is the maximum voltage of your transmitter battery when it is “full”. The battery that comes shipped with the Taranis is a 6 cell NiMh (Nickle Metal Hydride) battery. When fully charged the battery will read about 8.4 volts and when most of it’s useful charge is gone it will read about 6.6 volts although the battery will still work down to slightly lower than 6 volts before the transmitter shuts off. The battery meter is just an indication of the remaining capacity in the battery. I use 7.0 volts as the bottom of my meter and 8.4 volts at the top. If you use a 2 or 3 cell LiPo or LiFe battery, set the range to suit your battery. When finished setting the Battery meter range press “-” to move down to Sounds.
- Sounds controls when you hear sounds (beeps, warnings, voice tracks, and background music) and how loud they are. The speaker on the Taranis is very small the volume it can output is relatively low. What may sound as a relatively loud sound in a quiet room, can be very quiet when you are out of doors. Adjust your volumes accordingly. Of course, the settings can always be changed.
- Mode controls when sounds play. The options are: All, NoKey, Alarm, and Quiet.
- All plays all sounds
- NoKey plays all sounds except key presses
- Alarm only plays alarms such as low RSSI and battery warnings
- Quiet plays no sounds at all
- Volume is a slider. It is the master volume control. All other volume controls are relative to the volume set here. (Example: Volume is set at half and Beep Volume at full. The maximum Beep Volume will be half.) To adjust Volume highlight it’s slider and press ENT. The “+” and “-” keys increase and decrease the volume. When the slider is where you want it, press ENT. Then, press “-” to move down to the next slider.
- Beep Volume is just what the name implies. Adjust the slide to the volume you desire. If you want to hear the how loud the beep sound is, move down to the Wav Volume and move the slider all the way left or right. Each time a slide hits it’s “stops” it will beep. You can use this same technique to hear the differences in Beep Length and Beep Pitch.
- Beep Length the length of time the beep tone is played. There are 5 settings from extra short to extra-long. Adjust the slider to your preference.
- Beep Pitch adjusts the pitch of the beep upward in 15 Hz increments. The tone cannot be lowered below 0. Adjust the beep tone to your preference, then move down to Wav Volume.
- Wav Volume controls the play back volume of mono sound track recordings in Waveform Audio File (wav) file format. These are the files that are played using the Play Track option in Special Functions.
- Bg Volume controls the play back volume of wav files that are played using the Background Music option in Special Functions.
- Variometer a variometer (or vario) is a device that reports the increase or decrease in altitude of an aircraft. The FrSky variometer sensor can do this as text on one of the telemetry screens, as audio alerts, and by increasing or decreasing the pitch of a tone. Variometer sensors are typically used on sailplanes, but modelers have found uses for them on other craft as well. If you do not have a variometer sensor, you can skip the Variometer settings and move down to Haptic.
- Volume adjusts the volume of the vario tones.
- Pitch at Zero is the pitch in Hz of the tone played when the vertical speed is between the Sink Min and Climb Min values defined in the Telemetry panel. The value can be set from 300 Hz up to 1100 Hz.
- Pitch at Max is the vario pitch at maximum vertical speed as defined in the Telemetry panel (Climb Max). The value can be set from 700 Hz up to 2900 Hz. As the rate of climb increases the pitch of the tone will increase linearly from the Pitch at Zero to the Pitch at Max. The Pitch at Max must always be greater than the Pitch at Zero.
- Repeat at Zero – The delay in milliseconds between beeps. The range is from 200 (5 beeps/sec) up to 1000 (1 beep/sec). Vario tone is continuous when below the Sink Min value defined in the Telemetry panel. The tone repeats at the Repeat at Zero rate when between the Sink Min and Climb Min values. When the vertical speed is above the Climb Min value the rate of the tone increases linearly to about 12.5 beeps per second (80 Ms) at Climb Max vertical speed.
- Haptic is a tactile feedback option which can be added to the Taranis. Adding the new haptic components to the Taranis requires intermediate to advanced level soldering skills. Haptic is built into the Taranis Plus which will be available “soon”. If you do not have Haptic on your Taranis, you should skip down to Contrast.
- Mode controls when sounds play. The options are: All, NoKey, Alarm, and Quiet.
- All vibrates any time a sound would play.
- NoKey vibrates any time a sound would play except key presses
- Alarm only vibrates for alarms such as low RSSI and battery warnings
- Quiet does not vibrate
- Contrast adjusts the display contrast. The minimum is 0, the maximum is 45, and the default contrast is 25. Press ENT to edit the contrast. Press the “+” and “-” keys to get the contrast that’s best for you, then press ENT to exit Contrast adjustment.
- Alarms allows you to select which alarms alert you, and in some cases when.
- Battery Low allows you to set the alarm voltage for the transmitter battery. When the battery reaches this voltage you can be alerted by a voice alert or haptic (vibration) depending on your equipment and settings. A safe value for the 6 cell NiMh battery shipped with the Taranis is 7.0V. Adjust the value to suit your particular battery and preferences.
- Inactivity sets the time in minutes the Taranis can be inactive (no movement of sticks, buttons, sliders, etc.) before receiving a voice (and/or haptic) alert. A value of zero turns off the alert.
- Memory Low allows you to be notified when the Taranis begins to run low on memory. This is a handy alarm to have on if you run LUA scripts. The check mark will toggle each time you press ENT.
- Sound Off will alert you if you inadvertently turn off all sounds thereby blocking alarms. The check mark will toggle each time you press ENT.
- Backlight allows you to select when the display backlight turns on, how long it stays on, and how bright it will be.
- Mode determines when the backlight turns on. The options are: Off, Keys, Sticks, Keys + Sticks, and On.
- Off the backlight never turns on
- Keys the backlight turns on any time you press one of the 6 menu buttons
- Sticks the backlight turns on any time you move one of the sticks, or switches, but not the sliders or pots (S1 or S2)
- Keys + Sticks the backlight turns on any time you press one of the 6 menu buttons or move a stick or switch.
- On the backlight turns on and stays on
- Duration the length of time the backlight stays on after being activated (does not apply when the Mode is set to On).
- Brightness controls the brightness of the backlight. Values between 0 (backlight off) and 100 (full brightness). Adjust this setting to suit your preference.
- Color changes the color of the display (only available on the Taranis Plus)
- Alarm turns on the backlight when an alarm condition occurs. The check mark will toggle each time you press ENT.
- Splash Screen the time the splash screen (the opening screen when the transmitter powers on) stays on in seconds.
- GPS Time zone specifies Universal Time Coordinated (UTC) Offset for local longitudinal time zone (-12 through +12). For example the GPS Time zone for New York City is -5 except during Daylight Saving Time when it is -4.
- GPS coordinate formatthe format in which GPS coordinates are displayed. The options are DMS and NMEA.
- DMS displays the coordinates in degrees, minutes, and seconds
- NMEA displays the coordinates in degrees and decimal minutes
- Country Code sets the radio to be compliant with the regulations on your region. The options are America, Japan, and Europe.
- Voice Language the language to be used for voice alerts. The default is English which is the only language shipped on the Taranis SD card. Other languages can be downloaded through the download function of Companion.
- Units the units used in telemetry displays, and voice alerts. The options are Imperial (used in the USA and a few other countries) or Metric (used by most of the rest of the world).
- FAI Mode disables all telemetry except RSSI and battery voltage (A1/A2) to comply with the FAI international rules for competition. Once enabled FAI Mode cannot be changed without reloading the Taranis firmware. This option only appears if FAI choiceis selected as part of the firmware options in Companion.
- Play Delay (sw. mid pos) delays playing wav files associated with the mid position of 3 position switches when switching from one position to another, unless the switch remains in the mid position for longer than the time specified in milliseconds (1000ms = 1 second, 500ms=1/2 second, 330ms=1/3 second, etc). For example if you have wav files that play “High Rate”, “Mid Rate”, and “Low Rate” when switch A is in the top, mid, and bottom positions. Without a play delay, the “Mid Rate” file would play when switching A quickly from bottom to top. Setting Play Delay to 300ms would prevent “Mid Rate” from playing unless the switch lingered on the middle position for longer than approximately 1/3 of a second.
- Default channel order determines the order in which the four primary controls (Rudder, Elevator, Aileron, and Throttle) are inserted on channels 1-4 when creating a new model. Default channel order only determines the channel order assigned to the primary controls, and the order in which channels are assigned in the Trainer screen. Any order of the 4 primary controls (T, A, E, and R) can be selected. TAER is the default for Spektrum/JR, and AETR is the default for Futaba/Hitec,
- Mode determines which sticks move which controls on the airplane. The vast majority of RC pilots use either Mode 1 or Mode 2. Click on Mode and change the values. You can see on the display how the controls assigned to the sticks change. Most pilots in Europe fly with Mode 1 (Elevator and Rudder on the left stick and Throttle and Aileron on the right stick), while most US pilots prefer Mode 2 (Rudder and Throttle on the left stick and Aileron and Elevator on the right stick). Mode 3 and 4 are available, but I never heard of anyone using them. Mode 3 reverses the stick assignments of Mode 2, and Mode 4 reverses the assignments of Mode 1. Pick the Mode you prefer and when done press EXIT.
The next class in this series “Basic Airplane Set Up on Taranis” will be based on Mode 2 with AETR as the Default channel order. If you set your transmitter up the same way now, the class will be much easier to follow. You can always change the Mode or Default channel order to something else later.
You are finished with Radio Setup. Your Taranis should light up, beep, and squawk just the way you want it to. If you don’t like how something is setup, go back and change it. That’s the beauty of this radio. You can make it perform just the way you like.
That’s all the hard work out of the way. Out of the 8 General Radio Settings pages, you have already visited 3 of them. Radio Setup, Calibration, and Analog Inputs (where you set the battery calibration). Now it’s time to take a look at the other General Radio Settings pages, and discover more about your Taranis. Let’s move on to the next lesson the Taranis General Radio Settings.