Before building your quadcopter, Radio Transmitter should be one of the first few items you need to look at. It’s a common question for RC beginners, how to choose a suitable RC transmitter.
In this article we will discuss the basics of a transmitter (RC Controller) and what you should look for when buying one: price, the number of channels, modes, frequency and other features.
Article was first created in October 2013, updated in June 2016.
Table of Content
- Frequency Technology
- TX / RX pairing
- What to look for when buying a transmitter
- Why invest in good TX
- Transmitter Recommendation
The number of channels determines how many individual action on the aircraft can be controlled.
For example, channel 1 for throttle, channel 2 for yaw (rotating right and left), channel 3 for pitch (pitch or lean forward and backward), channel 4 for roll (roll or leaning left and right).
As you can see, four channels is the minimum number of channels needed to control a quadcopter (pitch, roll, throttle, yaw).
If there are additional channels on a transmitter, they are normally used as AUX channels for switches and pots (potentiometer or knob). You can use them to change flight modes or trigger certain function/features on the multirotor.
In general it is recommended for transmitters to have at least 5 or 6 channels for a quadcopter. The extra 1 or 2 channels can be used to arm the quad and/or switch between different flight modes.
Transmitters with more channels (6+) are generally more expensive. They tend to have better build quality and are more functional than a basic 4 or 5 channel RC transmitter.
The stick control on a radios TX is called a gimbal. (don’t get confused with camera gimbal :D )
There are 4 different Modes – mode 1, mode 2, mode 3 and mode 4. These are basically the different control configurations.
Mode one configuration has the elevator control on the left joystick and the throttle on the right one.
Mode two is the most common for quadcopter because the stick represents the movement of your quadcopter. It has the elevator control on the right joystick and the motor throttle on the left one. The right joystick self centres in the both axis, whereas the left joystick only self centres in yaw axis (left/right direction) and clicks or slides in the throttle (up/down) axis in order to allow constant throttle.
Mode three – same as Mode one except Aileron and Rudder are swapped.
Mode four – same as Mode two except Aileron and Rudder are swapped.
Because of the identical gimbals configuration, in some TX, Mode 1 and Mode 3 are exchangeable, so as Mode 2 and Mode 4. This is achieved by swapping Aileron (roll) and Rudder (yaw) channels in user settings.
Common frequencies used in RC radio are 2.4GHz, 27MHz, 72MHz, 433MHz, 900MHz and 1.3GHz. Don’t worry about all these numbers, majority of us use 2.4GHz these days, unless you have specific needs for a different frequency. Just in case you are interested here is some brief and interesting technical background.
For those of you who have been around the RC scene for some time, you will remember 27MHz and 72MHz with the frequency/channel crystals (crystals were tuned to specific frequency channels to transmit the signal to the receiver which had its own same channel crystal essentially binding them together). This technology has been around for decades, they allow longer range and better signal penetration. However you could interfere with others using the same frequency (even different brands). Another problem was the large size of the antennas as they could reach a few feet in length. Crystals used for channel selection were also inconvenient as they broke easily and could constantly and annoyingly change when flying/driving with others.
Nowadays the 2.4GHz system is a newer technology, and it’s currently the most common frequency for small RC ground and air vehicles. It becomes the RC standard after new protocols were created that introduced frequency hopping technology which allowed the user to not have to worry about picking up frequencies or channels from other pilots. Antenna is smaller and easier to carry, but usually with shorter range than the 27/72Mhz.
You may have also heard of others using 1.3ghz, 900mhz or 433MHz equipment, these are more commonly used for long range or on larger crafts.
All the transmitter manufacturers switched to the new channel hopping protocols which made RC very easy to maintain and use. The software running is constantly scanning for the best frequency to use and if it detects any interference, automatically switches to another available channel. It is doing this many times per second so you never experience glitches or radio interference which was a big problem in the RC industry for many years. Another good thing about channel hopping is that you can fly with many other people at the same time without getting interference.
A transmitter usually comes with a receiver. Be aware that some brands of transmitters are only compatible with (or limited to) their own brand or model of receivers. That means when the receiver is broken you would normally have to get the same one.
This is not always the case though, as there are now lots of options that can be paired with other receivers that are using the same protocol (for example spektrum). Make sure you check and ask the shop for advice before purchasing.
Binding the transmitter to the receiver is very simple, and is only required to do so at the first time you setup a new receiver with the transmitter. Most decent TX will allow you to bind multiple receivers to the TX, and save each one with different settings (aka models, or profiles). Check the instructions for binding procedures that comes with the receivers.
Budget and Channels
The price range is huge, from as cheap as $20 to well over $1000. The cheaper the radio, the lower quality it would be (casing, gimbals, switches etc), and the fewer channels you are going to get.
If you have a tight budget and not committed to the hobby, it would make sense to get a cheap 5 or 6 channel one, just to get a taste of flying, and later on upgrade to a better transmitter when you are more experience and know what to look for. It’s a good idea to have a backup transmitters anyway.
However if you are serious about quadcopters and someday want to run GPS navigation, gimbal control etc, it’s better to get 8 channels or more.
Hardware and Features
There’s a lot to consider when it comes to choosing a good transmitter, such as the display screen (if there is backlight), how the sticks feel, multiple model memories and Training features (Buddy mode), and so on. Some may also like the expo and curve functions which allow you to change how the sticks react to your input by softening there feel at points you setup. (although this can also be done in the flight controller firmware, which is actually preferred by many pilots so you don’t change the sticks resolution and inputs on the radio)
Some RC transmitters support programming and firmware flashing to enhance user experience. You can personalize them with music and voice recordings or whatever you’d like. Do your research before spending good money on it.
An RC transmitter is a long term investment.
With programs available such as cleanflight, we can setup the additional channels to tune the quads in flight. This makes having a transmitter with additional AUX channels a big benefit. Having the ability to save multiple models is an added benefit of having a better radio as this allows one transmitter to be used for multiple craft.
Another benefit of a high end transmitter is the possibility of direction connection to computer via USB, and use it for flight simulators. You can get used to the feel of the sticks/controls, this not only benefits you by speeding up the learning curve, but also helps improve your skills even when you become an advanced pilot. Simulators also allow you to use your own transmitter so that you can practise with it and get to know its functions very well before you even use it to fly your actual quad. Some cheap transmitters can also do this but requires a lot more tinkering and accessories.
For a low budget build, Turnigy 9X is relatively affordable, and has a lot of room for DIY/Upgrade modifications! See my review about this Transmitter.
The 9XR or 9XR-Pro is a step up from the 9X. It has similar functionality to other higher end transmitters but comes in the most basic forms to keep costs super low. It is programmable so you can modify it and flash various types of transmitter firmwares on it, has the ability to load custom sounds, music to program to the switches and different functions. Since it also uses external modules you can use it with a couple of different protocols such as Frsky, Orange (dsmx/dsm2). There are many mods that can be done and there is a whole open source community surrounding it which gives its users endless options.
If you have enough budget, check out the Frsky Taranis. It is one of the best reasonably priced transmitters and has swept the FPV industry to become the most popular transmitter.
Other options for higher end units are the Futaba T10/T18, Spektrum DX9/DX18, JR-XG11/XG14 among many others. See this comparison review of the DX6 and Taranis by Artur Banach.
Something else to consider if you plan to stick with the hobby and maybe are looking for something more functional and advanced is tray style radio/transmitters. Tray style radios were traditionally used by plane pilots who needed layouts that gave them easy access to multiple switches and pots. Later the big industry UAV pilots turned to them as they gave them the most function and ergonomics with there needs for accessing various controls at once. They used to be very large, bulky and required shoulder straps to comfortably hold them. Since then, they have become nicer looking and smaller in form which has made them more accepted and popular.
An example of a really nice new tray transmitter that has been very much anticipated is the Frsky Horus. Not only is it functional and ergonomically superb, it looks really cool! Release date will be announced shortly as the last stages of beta testing are currently taking place now.
There are several tray transmitters out right now but tend be on the more expensive side. Can’t stress this enough, do your research before you buy something of this caliber as it will become a very big investment (depending how deep your pockets are).
DIY RC Transmitter
I attempted to build an RC Transmitter myself although I haven’t tested it yet with a quadcopter.
There are other tutorials you might find interesting.