Radio Transmitter (TX) and receiver (RX) should be one of the first items to buy when building a quadcopter. It can be confusing to 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.
Table of Content
- Frequency Technology
- TX / RX pairing
- What to look for when buying a transmitter
- Why invest in good TX
- Transmitter Recommendation
- How to choose receiver – RX
What are a RC Transmitter and Receiver?
A RC transmitter (aka radio transmitter, or TX) is a device that allows the pilots to control the aircraft wirelessly. The signal/commands are then received by a radio receiver (RX) which is connected to the flight controller.
If you are new and interested in flying drones, you should check out the beginner guide to mini quad racing.
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 TX modes – mode 1, mode 2, mode 3 and mode 4. These are basically the different configuration of the 2 control sticks.
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. If you don’t know which mode to use, just go for mode 2 since it’s the most popular.
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 long enough, 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.
2.4GHz system is a newer technology, and it’s currently the most popular 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). So it’s important to know that not every TX would work with every RX, make sure you check and ask 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. You can even create separate model profiles for each aircraft so you can have different settings for each model. Check the instructions for binding procedures that comes with the receivers.
Once the TX and Rx are bound, the RX cannot be controlled by other TX.
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 (housing, gimbals, switches etc)..
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 do more advance stuff, like running GPS navigation, camera gimbals 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 (resolution, backlight etc), how the sticks feel (gimbals quality), 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 software, which is actually preferred by many pilots so you don’t reduce 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.
To be honest ergonomics is really a personal thing, no one can tell you which TX would feel perfect in your own hands. Factors like the weight of the TX, the location of the sticks and switches, how large your hands are, how long your fingers are, and so on all play a part in this.
I don’t think it’s a huge issue to worry about with the TX we suggested here. These companies are all brand names in the RC industry for years and they know how to make a good TX. If you can, go to a meetup and try a few. If you can’t that’s fine too. Speaking from experience, I think it’s just a matter of time getting used to a transmitter.
The longer I am flying quadcopters, the more I value Telemetry. It’s basically a feature that allows RX to send flight data back to the TX, such as RSSI, battery voltage, current draw etc.
There are 2 ways Telemetry data can be obtained: 1. external sensors connected to receiver; 2. flight controller sends data to receiver.
External RF Module Capability
It allows you to install an external transmitter module on the TX, in order to transmit on a different frequency (such as 433MHz rather than 2.4Ghz), or use with other brands of RF systems/receivers. For example, the Taranis with Orange module can bind with Spektrum receivers.
A decent RC transmitter is a long term investment.
With programs available such as betaflight, we can setup the additional channels to tune the quads PID and rates during 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 crafts.
Another “should have” feature is direct connection between TX and computer via USB, which allows you to use the TX for flight simulators without any other additional hardware or mods. Training in FPV simulators allows you to get used to the feel of the sticks/controls and build up muscle memory. Some cheap transmitters can also do this but requires a lot more tinkering and additional hardware.
Overview of some of the popular TX for FPV
When I started, I bought the Turnigy 9X. It’s affordable, and has a lot of room for DIY/Upgrade modifications! See my review about this Transmitter. But I later quickly sold it and bought an Taranis 9XD Plus instead as I needed more features.
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 firmware 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.
Back to the Taranis X9D I bought, it is very powerful for what it costs, making it one of the best value TX out there. It has swept the FPV industry to become one of the most popular transmitters. Here are a list of tutorials, mods and tricks for the Taranis X9D. You can also consider it’s cheaper version, the QX7.
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.
DIY RC Transmitter
I attempted to build an RC Transmitter myself although I haven’t tested it yet with a quadcopter.
How to choose receiver – RX?
It’s important to know that TX only works with radio receiver (aka RX) from the same manufacturer generally. For example, if you get the Frsky Taranis, you will have to use Frsky RX’s, or other Frsky compatible RX.
Your preference in receivers will limits what TX can you get, such as availability, size, receiver etc. For example, Frsky radio system was made super popular due to their receivers having compact form factor. which makes them perfect for mini quad builds.
In this list we rounded up all the popular Frsky receivers for mini quads and micro quads.
There is also consideration to what receiver protocols are allowed and technologies used – for more detail: Receiver RX Protocols and Technology.
Article was first created in October 2013, updated in June 2016.