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How to choose a wireless transmitter and receiver for drones?

Click:50 Time:2020-10-25 13:02:17

Today I wrote an article casually, introducing some basic knowledge of wireless transmitter (RC controller), and what you need to pay attention to when you want to buy it: price, channel number, mode, frequency and other characteristics.

When you want to get a quadrotor drone, the wireless transmitter (TX) and receiver (RX) should be the first thing you need to buy. For RC (Radio Control) beginners, how to choose a suitable RC remote control is very important. A good TX (remote control) can be used for many years, unlike other parts that are often damaged, so spend more money to buy a better one.

What are RC transmitters and receivers?

The wireless transmitter (ie TX) is a device that allows people to control the aircraft wirelessly. The signal/command is received by the wireless receiver (RX) connected to the flight controller.

Frequency and technology

The frequency of most wireless transmitters is 2.4GHz, which is currently the most popular frequency. Lower frequencies are also feasible for long-distance types, such as 433MHz and 900MHz.

After the frequency hopping technology protocol was created, 2.4GHz became the standard frequency for remote control. It will automatically find available channels to avoid conflicts with other pilots, allowing many players to fly at the same time.

The advantage of 2.4GHz is that it has a smaller antenna which makes it easier to adapt. But its remote control distance is shorter than that of low frequency.

Balance frame

The joystick of the wireless transmitter is called gimbals (don't confuse it with the gimbal stabilization: D).

The quality of the gimbal is one of the most important considerations when you become a drone player. The gimbal may have little effect when you start playing, but it may become a bottleneck for you to fly better.

A popular technology is the Hall sensor, which uses a magnet to detect the position of the rocker instead of a traditional potentiometer. It is therefore more durable and more accurate. Regardless of the type of gimbal, generally you can manually adjust the tension of the balance bar. To adjust this tension you need to turn on the remote control. There should be a tutorial in the user manual.

Another factor to consider is whether you prefer to use your thumb or pinch to control.

People who like to use their thumbs usually want a shorter lever and a narrower remote control so that they can grasp the back of the remote control.

People who like to hold the control want a longer lever and distance, but be careful not to touch other switches. If you haven't set any switches, don't worry. The pinch may require a strap. How to control them is not good or bad, it's just personal preference.

Ergonomics

Ergonomics may be a more personal matter, and no one can tell you which remote control will feel better or worse in your hands. The weight, the position of the rocker and switch, the size of your hand, and the length of your fingers are all influencing factors.

I don’t think we need to worry too much. These companies are brands in the RC industry for many years, and they know how to design the best remote control. If you are still not at ease, you can try someone else's remote control.

switch

The transmitter is not only a gimbal, but also a set of switches, you can use them to change the flight mode, etc.

In addition to sliding and turning the knob, the switch has two or three positions. But in most cases, beginners don't need it.

I think a maximum of two switches is sufficient for quadrotor aircraft. Of course there are more.

Channel

Each control or switch requires a channel to send a signal to the receiver.

Two gimbals require 4 channels, namely throttle, yaw, pitch and roll. Additional channels are sometimes called "backup channels" because they can be used as backup controls, such as switches. For example, for a 9-channel wireless controller, you have 5 remaining channels, which you can use as switches and knobs. The picture below has 4 channels on the right and 12 channels on the left-because there are 8 switches.

In general, quadrotor drones are recommended to have at least 6 channels. The extra one or two channels can be used to control rotors and switches in different flight modes. It is always good to have more channels.

If you operate a competition drone, you don’t need too many channels. Personally, I usually use 8 channels: 1. Pre-position switch; 2. Buzzer switch; 3. Mode switch; 4. Transmit RSSI signal.

The number of channels you can use is also limited by the receiver protocol (the connection between the receiver and the flight controller). For example, SBUS can support 16 channels, while PPM can only support 8.

Wireless receiver

A wireless receiver (RX) is a device that receives commands from a wireless transmitter. It then transmits the signal to the flight controller. This is how you control the drone.

What you need to know is that a TX is usually only paired with the same brand of wireless receiver (ie RX), and the protocol must be consistent. For example, a Frsky Taranis TX cannot work with a Spektrum receiver.

"Transmission protocol" (I sometimes call it "air protocol") is a language between transmitter and receiver, and different brands have different protocols. Even the same brand may have different agreements.

When you buy a remote control, you need to realize that you also limit yourself to their receiver. This is an important consideration: some brands of receivers are more expensive; some brands of receivers are more lightweight and suitable for mini quadcopters; some brands have no specific functions.

Connect TX and RX

To establish the connection between the wireless transmitter and receiver, you first need to connect them.

Only need to connect once between TX and RX. When you change the firmware of the TX or RX module or bind the RX to a different TX, the connection will fail.

The connection process is usually very straightforward, but different models may be different, please refer to the user manual.

Note that you can bind multiple receivers to the same TX, so you can control multiple drones with the same transmitter.

How to choose a receiver

Your preference for the receiver will affect your principles for the remote control. For example, Frsky wireless systems are very popular due to the compactness of their receivers. This makes them the first choice for making mini quadcopters.

It is also necessary to consider the allowed receiver protocols and technologies used, such as PWM, PPM, and SBUS. usually,

Due to the delay factor, SBUS is better than PPM. At the same time, they are better than PWM because they require less wiring harness.

Remote control range

There are many factors that affect your scope.

l The obstacle between TX and RX can greatly reduce the range;

l Transmitter output power, higher power means greater range, but you must pay attention to legal restrictions;

l Receiver sensitivity, the more sensitive the range is;

l Receivers are diversified, some "full range" receivers provide two antennas for diversity;

l Antenna layout.

Generally speaking, the best 2.4GHz wireless allows you to get a range of 300m to 1.5km. If you want a longer range and stable signal, you need to invest in a "long range" RF system. For example, TBS Crossfire or Frsky R9M, which use lower frequency bands.

External module support

The transmitter has a built-in RF (Radio Frequency) module to transmit signals to the receiver, but it will be useful if they support external modules. These transmitters have a module slot, and you can easily install external transmitter modules. This allows you to use other brands of protocols or different power and frequency.

For example, I installed this "multi-protocol module" on my Taranis, so I can bind it to many toy drones.

TBS Crossfire and Frsky R9M are some other well-known external modules. These modules run at 900MHz and are designed to be used in a long range.

operating system

Each wireless system has its own operating system (OS-operating system), which usually refers to the user interface.

Most manufacturers have their own OS, but the one I want to introduce to you is Open TX. This is an open source OS that can adapt to many TXs on the market. Some popular wireless systems also use OpenTX. It may be difficult to learn at the beginning, but it is one of the most powerful and configurable radio systems.

Telemetry support

It is a very useful feature for the receiver to send flight data to the pilot, such as RSSI, battery voltage, traction current, etc.

In OpenTX, you can choose to display the telemetry data on the screen or use voice prompts.

Why invest in a good launcher

A good wireless transmitter is a long-term investment.

Using programs such as betaflight, we can set up additional channels to adjust the drone's PID and frequency during flight. This is a big advantage of transmitters with additional AUX channels. A good wireless system that can store multiple models allows one transmitter to be used on more aircraft.

Another "should have" feature is the direct connection between the TX and the computer via USB, which allows you to simulate the flight directly on the computer software without additional hardware or modes.

Some popular TX options for FPV:

Flysky fs-t6 6 channels Spektrum dxe 6 channels Turnigy evolution 8 channels Turnigy 9xr 8 channels Frsky Taranis Q x7 16 channels Frsky Taranis x9d plus 16 channels Frsky horus x10s/x12s 16 channels

Some suggestions about wireless transmitter

Currently my favorite models are Taranis X9D Plus and Taranis QX7.

l They all use powerful open source firmware, OpenTX

l Adapt to a wide range of Frsky receivers, such as PWM, PPM, SBUS, and inexpensive, small in size and light in weight

l QX7 has fewer switches and lower screen resolution than X9D, but it is more than enough for quadcopters. Some people even say that the QX7 has a better grip than the X9D. Of course, it really depends on you.

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