This tutorial explains the basics of a radio transmitter for racing drones, what you should look out for when buying one: price, the number of channels, modes, frequency and other features.
A radio transmitter (TX) and receiver (RX) should be one of the very first items to buy when getting into FPV. It can be confusing for beginners which radio to buy as there are so many options on the market. Unlike many other components and accessories that often break or become obsolete, a good radio can follow you for many years so it’s okay to invest a bit more on a decent one.
If you are new, make sure to check out the beginner guide to mini quad racing.
Table of Content
- Frequency & RF Technology
- Radio Receiver
- External Modules Support
- Operating System
- Why invest in good TX
- TX Options
- Transmitter Recommendation
- How to choose receiver – RX
What are Radio Transmitter and Receiver?
A radio transmitter (a.k.a. TX) is what the pilots use to control the aircraft remotely. The signal/commands are received by the radio receiver (RX) which is usually connected to a flight controller.
Most RC transmitters work on 2.4GHz, it’s become the standard for radio control after new protocols were created that introduced frequency hopping technology. It basically looks for available channel automatically to avoid interfering with other pilots, allowing multiple pilots flying at the same time.
Other frequencies are also available for RC, such as the popular 900MHz Crossfire system – a system that is designed for long range flying.
The stick controls on a radios TX are called gimbals. (don’t get confused with camera gimbal )
Gimbal quality becomes one of the most important considerations as you grow as a pilot.
It can affect the handling when flying a drone, and the smoothness of your control. It might not matter much at the beginning when you are just starting, but it can become a bottleneck to how good you can fly.
One popular technology is hall sensor gimbal that uses magnets to detect the stick position rather than the traditional potentiometer. It’s more resistant to wear and precise.
Regardless the type of gimbals, you should normally be able to adjust the tension in the sticks, which can also help tremendously (here is my guide on adjusting stick tension for the Taranis and other popular radios).
Another thing to consider is whether you are a pincher or thumber? The difference is in how you hold the sticks.
Thumbers typically want shorter sticks and a narrower radio so that they can grip the back.
A pincher might want longer stick and travel but will have to beware of any potential switches they could knock by accident. They may also require a neck strap.
There is no right or wrong way to hold them, purely just personal preference.
Ergonomics is very much a personal thing, no one can tell you which radio would feel good or bad in your own hands. Considerations such as the weight, the location of the sticks and switches, how large your hands are, how long your fingers are, all play a part in this.
In my opinion, it’s not a huge issue to worry about though with the radios we recommend on this page. These brand name companies have been in the RC industry for long enough to know how to make a good TX.
The best thing to do is probably going to a local meetup and try a few different radios from other pilots.
Transmitters don’t just have gimbals, they also have an array of switches you can use for arming and changing flight modes etc.
Switches come in two or three position forms as well as sliders and rotary knobs. However as mini quad pilots we don’t really need too many compared with plane flyers.
I think having a at least 2 switches are enough for mini quad flying. Of course it doesn’t hurt to have more.
Each control or switch requires a channel to send the signal to the receiver.
The two gimbals take up 4 channels, throttle, yaw, pitch and roll. The extra channels are sometimes called “AUX channels” because they can be used for auxiliary controls such as switches. For example, for a 9-channel radio, you have 5 spare channels you can use for switches and knobs.
But for hobby grade quadcopters, you definitely want more channels and controls.
In general it is recommended to have at least 6 channels for a quadcopter. The extra 1 or 2 channels can be used to arm the quad and switch between different flight modes. It would be desirable to have even more channels.
You don’t need a lot of channels for flying racing drones. Personally I only use 8 channels most of the times: 1. arm switch; 2. buzzer switch; 3. flight mode switch; 4. passing RSSI signal.
The number of channels you can use is also limited by the receiver protocol (the connection between receiver and flight controller). For example, SBUS can support up to 16 channels, while PPM can only support up to 8.
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.
There is no right or wrong which one to use, just what you are more comfortable with. If you don’t know which mode to use, just go for mode 2 since majority of the pilots are using it, and it’s going to have a higher resell value later on.
A radio receiver, or RX, is the device that receive commands from the radio transmitter. It will then pass the signal to the flight controller and that’s how you control a drone.
It’s important to know that a TX normally only works with radio receiver (aka RX) from the same brand, and the same “TX protocol”. For example, a Frsky Taranis TX won’t work with a Spektrum receiver.
The “TX protocols” (I sometimes call it “air protocol”) is like a language spoken between the transmitter and receiver, and different brand have different protocols. Even within the same brand they might have different protocols.
When you buy a TX, you need to realize that you are also locking yourself into their receivers. This becomes an important consideration: some brands of receivers are more expensive than others; some brands might have a better selection of light weight receivers for mini quad; Some brands don’t have certain features such as telemetry…. etc…
Remember, you are going to put a receiver in every quad you build so this adds up quickly in the long run if you ever build more drones.
Binding TX and RX
To establish communication between a radio transmitter and a receiver, you must bind them first.
Binding of TX and RX only needs to be done once. You will lose the bind when you change the firmware of either the “TX module” or RX, or after binding the RX to a different TX.
The binding process is usually straightforward, but might differ from model to model, please refer to the manual.
Note that you can bind multiple receivers to the same TX, so you can control multiple drones using the same transmitter. But you can only bind the RX to one TX.
How to choose receivers
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, such as PWM, PPM and SBUS. Generally speaking, SBUS is better than PPM because of latency, while they are both better than PWM because of the number of connection required. For more detail: Receiver RX Protocols and Technology.
There are many factors that can affect the range of your RC link.
- Line of sight gives you the best possible signal, obstacles between your TX and RX can significantly reduce range
- Transmitter output power, higher power means longer range but beware of legal limitation
- Receiver sensitivity, the more sensitive the better the range
- Receiver diversity, some “full range” RX offers two antennas for diveristy
- Antenna placement
Typically, the best 2.4Ghz radio might give you 300m to about 1.5Km range. If you want to go further with reliable signal, you will want to invest on “long range” RF systems. For example the TBS Crossfire or Frsky R9M that utilize lower frequency bands.
External Module Support
Transmitters have built-in RF module to send out signal to the receivers, but it’s very useful if they support external modules too. These transmitters have a module bay, and you can install an external transmitter module easily. This allows you to run protocols of another brand, or different power and frequency.
For example, I installed this “Multi-protocol module” in my Taranis, so I can bind it to a lot of toy grade quadcopters.
Other famous external modules are the TBS Crossfire and Frsky R9M, these modules operate on 900MHz and are designed for long range.
Every radio has its own operating system (OS), which is basically the user interface.
Most manufacturers have their very own OS, but the one I want to introduce you to is OpenTX. It’s an open source OS that is compatible with many TX on the market. Some popular radios even come with OpenTX.
It might be a little harder to learn at first, but it’s one of the most powerful and configurable radio system out there
It’s an useful feature that allows receiver to send flight data back to the pilot, such as RSSI, battery voltage, current draw etc.
In OpenTX, you can choose to display Telemetry data on the screen, or have it played as audio warnings.
Why invest in a good transmitter
A decent radio 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.
Popular TX Options for FPV
|Flysky FS-T6||6||$56||Banggood | Amazon|
|Turnigy 9XR||8||$111||Amazon | GetFPV|
|FrSky Taranis Q X7||16||$120||Banggood | Amazon | HorusRC|
|T16 Pro Hall||16||$160||Amazon|
|Flysky Nirvana||16||$180||Amazon | Banggood|
|Frsky X-Lite||$140||GetFPV | Banggood|
|Frsky X-Lite Pro||$200||RDQ|
|Frsky X9 Lite||$90||Banggood | GetFPV | Amazon|
|Spektrum DX6e||6||$180||RMRC | Amazon|
|FrSky Taranis X9D+ 2019||16||$250||Banggood | Amazon | HorusRC|
|TBS Tango||10||$250||Amazon | GetFPV|
|Frsky Horus X10S||16||$470||HorusRC|
|FrSky Horus X12S||16||$500||Amazon | GetFPV | HorusRC|
|Spektrum DX9 Black||9||$600||Amazon|
Recommendation on a Radio Transmitter
My personal favorite currently are the Taranis X9D Plus, and the Taranis QX7.
- They both use the powerful open source firmware, OpenTX
- Compatible to a wide range of Frsky receivers, which supports PWM, PPM, SBUS, and they are affordable, small and light weight
- The QX7 has fewer switches than the X9D, and the screen is of lower resolution, but that’s completely fine for mini quad’s. Some even says the QX7 has a better grip than the X9D, but of course that’s very much personal
Update (March 2017) – Frsky released a X9D SE (Special edition) that has many upgrades to the original version: M9 Gimbals, special “carbon fibre” housing, better switches
I Started with the Turnigy 9X
When I started, I bought the Turnigy 9X. It was an affordable option for $60, and has a lot of room for DIY/Upgrade modifications! See my review about this Transmitter. But I quickly grew out of it and bought an Taranis 9XD Plus as I needed more features, and receiver options.
The 9XR-Pro at the time just came out, it was 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 low. It is programmable so you can modify it and flash various types of transmitter firmware on it. 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.
Upgraded to the Taranis X9D Plus
It was tempting but I’m glad I got the X9D Plus instead. The X9D 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 radio transmitters. Not to mention the large range of small size receivers and very useful telemetry system. Here are a list of tutorials, mods and tricks for the Taranis X9D. You can also consider it’s cheaper version, the QX7.
Other higher end options 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
Back in 2013 I attempted to build an RC Transmitter myself but I haven’t tested it yet with a quadcopter.