How to Choose Radio Transmitter and Receiver for your Racing Drone

In this post, we are going to discuss about the radio controller or transmitter and the factors you should take into consideration including the price, number of channels, modes, frequency and other salient features.

When building your first quadcopter or racing drone, a radio transmitter and receiver are the first things that you ought to buy. Choosing an appropriate radio controller is one of the trickiest choices that drone pilots have to make. In contrast to other components that are liable to being worn out and damaged, a decent transmitter can last a lifetime. So, it is judicious to spend more money on a sophisticated transmitter of better quality.

What is a Radio Transmitter and Receiver?

A radio transmitter or controller is a device that lets the pilot maneuver his device wirelessly. The instructions are then received by a designated receiver which is connected to a flight controller.

Channels

The number of channels is responsible for determining the number of separate actions that can be performed on the aircraft.

For example, throttle, yaw (rotating the aircraft left and right), pitch (making it move in the forward and backward direction), roll (roll left and right), all these actions take one channel. So, four channels are the minimum number of channels required for the pitch, roll, throttle and yaw operations.

However, more channels are required for hobby-grade quadcopters.

The additional channels on a radio controller are called as the Auxiliary Channels and come in the shape of switches and pots. They are also called as potentiometers or knobs. They can be utilized to switch on a number of other modes of flight or activate different features.

Radio Control-transmitter-channels

Generally, it is recommended to have 5 or 6 channels for a quadcopter. They can be used to arm the quadcopter and change between different flight modes.

Transmitters with more than 6 channels are more costly. They come with better build quality and boast more features in contrast to transmitters with lesser number of channels.

5-channel-transmitter-diagram-1

The stick control on a transmitter is called a gimbal. But you better not get it obfuscated with the camera gimbal.

Modes of Transmission

There are four multifarious modes of transmission namely mode 1, mode 2, mode 3 and mode 4. These are actually two disparate settings of the control sticks.

In the mode 1 setting, the altitude control is on the left joystick while the throttle is on the right one.

Mode 2 is the most traditionally used one among the drone enthusiasts as the stick represents the motion of the quadcopter. The altitude control is on the right and the throttle on the left. The right joystick centers itself automatically in both the axes, while the left stick self-centers only in the yaw axis (left or right direction). It clicks or slides in the throttle (up or down) axis for constant throttle control.

Mode1

Mode 3 is similar to mode one except that the Aileron and Rudder are swapped with each other. Mode 4, on the other hand, is similar to mode 2 except that the Aileron and Rudder are swapped with each other.

Owing to the identical setting of the joysticks, in some transmission modes, mode 3 can be exchanged with each other and same is the case with modes 2 and modes 4. This is accomplished by swapping roll with yaw in the user configurations.

mode3 and mode4

There is no right or wrong configuration. It simply is related to how comfortable you are with in relation to a certain configuration. If you are not sure which configuration to go with, opt for mode 2 since it is the most common one among dronies community and it will boast a higher resell value later down the road.

Frequency Technology

2.4GHz is the most commonly used frequency. Lower frequencies such as 27MHz, 72MHz, 433MHz, 900MHz and 1.3GHz allow for longer range and are rarely used in mini quadcopters.

Here is some interesting technical information for your perusal.

If you have been in the drone hobby for a significantly long time, you must be familiar with the 27MHz and 72MHz frequency ranges or channel crystals. Crystals were tuned to specific frequency channels to transmit the signal to the receiver which had its own same channel crystal essentially synchronizing them together. This technology has been around for a long time and allows for longer range and enables better penetration. However, interference could take place with others using the same frequency despite having transmitters of different brands. Another issue was with the larger size of the antennae as they could be as long as a few feet. Crystals used for selection of channels were also not suitable as they got attenuated easily and could constantly be affected much to the frustration of the pilot while driving or flying the unmanned aerial vehicle of RC car.

2.4GHz is a newer technology and is the most commonly used frequency nowadays for all small RC ground based and aerial vehicles. It became the standard frequency channel after the introduction of new protocols related to frequency hopping which took the worry of manually selecting channels away from the pilot. Moreover, the antenna is easier to transport and smaller in size but usually offer shorter control range as compared to 27MHz or 72MHz.

Other frequencies such as 1.3GHz, 900MHz or 433MHz equipment is commonly used for longer control range or with larger sized aircrafts.

All the manufacturers of transmitters have adopted the newer frequency hopping standards which has made the maintenance and usage of radio controlled devices easier. The software constantly searches for the most suitable frequency to use and in case of any interference detection, selects the next available channel. Since it is carried out several times in a second so a pilot never experiences any glitch or radio interference which have been huge issues in the RC vehicles industry in the past. Channel hopping also makes it possible for multiple drone pilots to fly their devices simultaneously in there vicinity.

Radio Receivers

A transmitter generally comes with a receiver. You should also keep in mind that more often not, a transmitter only functions with a receiver from the same manufacturer. For instance, if you get the FrSky Taranis transmitter, you will have to buy the FrSky Taranis receiver or the one which is compatible with the FrSky Taranis.

Synchronizing the transmitter to the receiver is extremely simple. It is only required for the first time when the transmitter and the receiver are being configured. Transmitters of better quality can be bound with multiple receivers. Separate model profiles for each aircraft can also be created so you can adopt different configurations for different models. Go through the configuration settings in relation to binding procedures that come in the original packaging.

Once a transmitter and a receiver are bound, the receiver cannot be controlled by the transmitter.

How to choose receivers?

Choosing a receiver will limit the options with respect to transmitters such as availability, size etc. For instance, FrSky radio systems were very popular because of their receivers boasting smaller size which rendered them useful for mini quadcopters.

You also have to take into account the receiver technologies and standards that are allowed such as PWM, PPM and SBUS. Traditionally, SBUS is better than PPM owing to its less delay in signal propagation while both of them are superior to PWM because of the number of connections required. Here is a useful post on radio receiver protocols and technology.

What to look for in a radio receiver?

Budget and channels

You can get a receiver worth as low as $50 and as high as $1,000.

If you are marred by budgetary constraints, it is judicious not to buy a Taranis worth $200 and get a cheap 6-channel just to get a better flight experience. And you can always get a better transmitter as you get more acquainted with the art and science of flying a drone. Otherwise, you can go for one of the transmitters that we recommend in the upcoming sections.

Hardware and features

There are a number of factors that need to be taken into consideration when opting for a better transmitter such as the integrated display screen, the quality of the joysticks, multiple model memories and training features such as buddy mode. Some users might also take a fancy to expo and curve features which allow the way how sticks react to a user’s input by softening their feel at points configured. This can also accomplished in the flight control software which is a way preferred by a number of pilots so you do not have to reduce the sticks resolution and inputs on the radio.

Some radio transmitters also allow for firmware flashing and programming that enhances user experience further. They can be personalized with music and voice recordings. Conduct a comprehensive research before you actually invest your money into buying an expensive transmitter.

Ergonomics

Nobody except you can let you know how a certain transmitter feels in your hands. Weight, location of sticks and knobs, the size of your hands, length of your fingers, all these factors have a role to play.

I do not presume it to be a bigger issue since the transmitters developed by leading manufacturers are of better quality. You can also get into contact with the drone community and try to find it out from your fellow dronies which transmitter is a better one and why.

Telemetry Support

Telemetry is a feature that I am falling in love with. The receiver transmits flight data to the transmitter such as the Received Signal Strength Indication, battery voltage, current draw etc.

External RF Module Capability

Using this feature, you can attach an external transmitter module rather than the integrated RF module. It enables the pilot to transmit on a different frequency such as 433MHz instead of 2.4GHz or use varying frequency systems or receivers from a different brand. For instance, the FrSky Taranis with Orange module is compatible with the Spektrum receivers.

Why to spend money on a good transmitter?

As mentioned above, a good quality transmitter is a long term investment.

Software such as betaflight, a pilot can configure additional channels to tune the quadcopters’ PID and rates mid-flight. So a transmitter with additional Auxiliary channels has its own benefits. The feature that allows storage of multiple models is another benefit that allows you use the same transmitter with multiple drones.

Another must-have feature is a direct connection between the transmitter and computer via USB. This lets you use the transmission for flight simulators without using any extra hardware or modifications. Getting hands-on practice on flight simulators gives you the feel of using the sticks and knobs of the controller and helps build up your muscle memory. Some low cost transmitters can also accomplish this but they require lots of modifications and extra hardware.

Recommendations on a Radio Transmitter

Taranis X9D Plus and Taranis QX7 are my personal favorites:

  • OpenTX is the firmware that is used by both of them
  • They provide support for a broad array of FrSky receivers that are compatible with PWM, PPM and SBUS. Moreover, they are low cost, light in weight and compact in size.
  • The QX7 has lesser knobs than X9D and the display is of lower resolution. That is not an issue for mini quadcopters. Some are of the view that QX7 feels better in hand as compared to the X9D, but that, of course, comes down to personal preferences.

FrSky released a X9D SE (special edition) that is an upgraded variant of the original version. It includes M9 gimbals, special carbon fiber enclosure and better switches.

My own experience

I bought the Turnigy 9X at the outset. It was a low cost device worth $60 and provides lots of options for customizations. Here is a review about the transmitter. But soon enough I switched onto the Taranis 9XD Plus as I was looking for advanced features and receiver options.

The 9XR Pro was introduced at the same time around which was an upgrade from the 9X. It had similar features to those boasted by higher-end transmitters but is available in the most basic shape to keep the cost down. It can be programmed so you can customize it and flash various types of firmware to it. Since if also utilizes different external modules so it can also be used with a few different standards such as FrSky Orange (dsmx/dsm2). You can carry out a number of customizations and there is a large open source community surrounding it which provides a wide array of options to the users.

It was quite tempting but I’m happy that I bought the X9D Plus. Considering the range of features it comes loaded with and its price range, the X9D Plus is a gem of a transmitter. It is one of the most popular transmitters out there. In addition, it supports a large number of compact sized receivers and handy telemetry system. Futaba T10/T18, Spektrum DX9/DX18, JR-XG11/XG14 etc. are some of the higher end options with regard to transmitters.

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