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.
A 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. Unlike other parts that often break or become outdated, a good TX can follow you for many years so it’s okay to invest a bit more on a decent one.
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 controller, 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 a 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, throttle, yaw (rotating right and left), pitch (lean forward and backward), and roll (roll left and right), each takes up 1 channel. And so as you can see, four channels is the bare minimum to control a quadcopter (pitch, roll, throttle, yaw).
But for hobby grade quadcopters, you definitely want more channels.
Additional channels on a transmitter are often called AUX channels (Auxiliary), in the form of 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 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.
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.
The most popular RC frequency is 2.4GHz. Lower frequencies are available for longer range such as 27MHz, 72MHz, 433MHz, 900MHz and 1.3GHz but they are rarely used in mini quad.
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 radio controller usually comes with a receiver (RX). It’s important to know that a TX normally only works with radio receiver (aka RX) from the same brand. For example, a Frsky Taranis TX won’t work with a Spektrum receiver.
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 do telemetry….
Remember, you are going to put a receiver in every quad you build so this adds up quickly in the long run.
Binding TX and RX
Binding the transmitter to the receiver is very straightforward, and is only required at the first time you are setting up 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.
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.
Budget and Channels
The price range is huge, from as cheap as $50 to well over $1000.
If you have a tight budget and not committed to spend $200 for a Taranis, it would make sense to get a cheap 6-channel just to get a taste of flying. And you could upgrade to a better transmitter later on when you are more experienced and know what to look for. Otherwise I think you should just get one of the decent TX we recommend in the next section straight away.
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.
Ergonomics very much a personal thing, no one can tell you which TX 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.
I don’t think it’s a huge issue to worry about though with the TX we suggested here. These companies are brand names in the RC industry for years and they know how to make a good TX. If you are still try to find out more, I would suggest to go to a local meetup and try a few from other pilots.
The longer I am flying quadcopters, the more I value Telemetry. It’s an useful feature that allows RX to send flight data back to the TX, such as RSSI, battery voltage, current draw etc.
External RF Module Capability
With this feature you can install and use an external transmitter module rather than the built-in RF module. It allows you to transmit on a different frequency such as 433MHz rather than 2.4Ghz, or use a different RF systems/receivers from a different brand. 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
|FrSky Taranis Q X7||16||$120|
|FrSky Taranis X9D Plus||16||$205|
|FrSky Horus X12S||16||$500|
|Spektrum DX9 Black||9||$600|
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
My personal experience from the beginning
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 super 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.
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 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.
- Oct 2013 – Article created
- Jun 2016 – Updated with popular TX options
- Jun 2017 – Article updated, added receiver info