This part will be a bit more technical but necessary if you want to pursue serenely in this hobby. There is a whole vocabulary that can be scary at first. We will quickly review the different elements that make up an FPV drone to demystify this universe, adding some practical information.
It is not essential to remember everything, but recognizing the role of each component will be helpful. You can come back to this later; this part is not a prerequisite for the rest of this article or even flying your first FPV drones with “Plug&Play” models (PNP/BNF/RTF).
Our FPV drones are very energy-consuming. They need batteries capable of delivering high power in a short time. We use mainly Lithium Polymer batteries, commonly called “LiPo”. Here are some essential characteristics of LiPo batteries:
- The number of cells, often from 1 to 6, defines the LiPo voltage. The nominal voltage of a Lipo battery cell is 3.7V. Therefore, a 4S LiPo will contain four cells in series and have a nominal voltage of 14.8V (3.7×4).
- The capacity (in milliamperes per hour) indicates the amount of current it can deliver during one hour, for example, 1500 mAh.
- The discharge rate to calculate the maximum quantity of current that a LiPo can deliver at a time. A 1500 mAh LiPo with a discharge rate of 100C, will be able to deliver continuously 1,5 x 100 = 150A. In general, they can deliver twice as much for a few seconds. This characteristic should be taken with a pinch of salt, as the manufacturers take a lot of liberties.
- The connector to plug the battery to our FPV drones or the charger. The most common is the XT60 or the XT30 for the smallest LiPos. The smallest flying machines like the TinyWhoops have even smaller connectors, like the JST, JST-PH, and BT2.0.
LiPos can be dangerous and must be used and stored safely. Here are some rules to follow to avoid unpleasant surprises.
Favor a quality charger (SkyRC, ISDT, etc.) supporting up to 6S and offering some useful options such as discharge, storage, internal resistance measurement, management of HV LiPos (High Voltage, being able to be charged to 4.35V per cell instead of 4.2V for a classic LiPo).
Do not charge too much nor too slowly, ideally at 1C or 2C (for example, at 2A for a 2000mAh LiPo).
Here are a few basic rules :
- Never fully discharge a LiPo (stop at 20% or 3,5V per cell) to guarantee a good lifetime. If a cell goes under 3V, it will undoubtedly be unrecoverable.
- Always stay close to your LiPos while they are charging.
- Always charge LiPos in “balance” mode to ensure that each cell is equally charged.
- When you don’t use a LiPo battery for a long time, switch it to storage mode (~3.85V per cell). It will preserve its life span.
- Keep your LiPos in a suitable container. Ammunition metal boxes are well suited. Remember that you have to remove the seal (to avoid the pressure cooker effect in case of a leak or fire). You can even add a piece of drywall to the bottom.
Propellers, also called Props, are characterized by :
- The size: the diameter, expressed in inches.
- The pitch. It is measured in inches, and without going into detail, it is comparable to the “pitch” of a screw (the air playing the role of the nut). The higher the pitch, the more the blades will be inclined.
- The number of blades.
Thus, a “50383” or 5×3.8×3 propeller will correspond to a 5″ diameter propeller with a 3.8″ pitch and 3 blades.
Often sold as a set of 4, they come in 2 pairs (one to turn clockwise (CW for Clock Wise), the other counterclockwise (CCW for Counter Clock Wise)).
The frame is the skeleton of our quads. It is on it that we will fix all the drone components. In 99% of the cases, they are made of carbon, a solid, rigid, and light material.
The frame is primarily characterized by the size of the propellers that you will be able to put in, so we frequently speak of 5″ frame, for example. Another way to describe its size is to use the distance between the axes of 2 motors (measured on a diagonal).
Another essential characteristic is its geometry. The choice is vast, but to limit ourselves to the principal geometries, we will list :
- The ” True-X “: the four arms crossing each other in a right angle format.
- The ” Wide-X ” or ” Squished “: the motors are closer together on each side. The propellers are less visible to the camera. This is a more common configuration for the Freestyle/Freeride/Cinematic.
- The “Stretched”: contrary to a squished configuration, the front, and rear motors are closer. It is a geometry that favors speed and that we find more on FPV racing drones.
The geometry of a frame’s bottom and top plates can also vary. We will talk about a “bus frame” when the body of the frame is long, it is more spacious for the electronics, and it allows you to place an HD camera at the front and a LiPo at the back without any difficulty.
This type of frame is generally heavier and therefore not compatible with racing. For FPV racing, minimalist frames like the Five33 are preferred.
These are the ones that turn the propellers and allow our FPV drones to fly. On a quadrotor, it is essential to know that two motors turn clockwise and the other two counterclockwise; otherwise, it would not be able to maintain a stable position because of the centrifugal force.
A motor is characterized by :
- Its size: a motor of type 2207 will have a stator of 22 mm in diameter and a height of 7 mm.
- Its rotation speed for 1V is indicated in kV, so a motor given at 2500 kV will turn at 2500 rpm per volt. If it is supplied with 4S (14.8V), it will turn at 37,000 rpm (2500×14.8).
- A recommended operating voltage range, usually 4S-6S
The ESC or Electronic Speed Controller
The Electronic Speed Controllers are also called ESCs. They are the ones that receive energy from the LiPo and transform it to the motors to run at the desired speed.
They use pretty advanced electronics and integrate software (firmware) to ensure their operation. This software can be updated or changed. We will mainly use BLHeli_S and BLHeli_32 (the most advanced) firmware.
There is one ESC for each motor. Sometimes they are “separated” and put on the arms of the FPV drone, but more and more, we find them in “4-in-1” format. In that case, they are joined together on the same electronic board in 20×20 or 30x30mm format (hole spacing for mounting).
In the case of 4-in-1, the LiPo is connected to the ESC board. For separate ESCs, they will have to be powered in another way, for example, by using a PDB (Power Distribution Board) like the Airbot Matrix, which will supply the power to the different components of the FPV drone.
ESCs receive information of rotation speed that each motor must have through a protocol that allows them to communicate with the “brain” of the FPV drone. Over time, many protocols have been developed. We will retain that a digital protocol imposed itself, the DShot. It is available under several declinations (DShot600, 1200, 2400, etc.) whose communication speed is more or less fast.
The FPV camera
Not to be confused with the HD camera (optional) dedicated to recording good quality video of the flights. The FPV camera films the image that we will have in our FPV masks or FPV goggles. Several formats are available, to be chosen according to the chassis that will host them: nano (14x14mm), micro (19×19), mini (21.8×21.8), full size (26×26).
Two types of sensors are the most common: CCD and CMOS, the latter being the most common today.
The cameras are equipped with a lens whose size defines their field of view (FOV for Field Of View). Some are optimized for a use 4/3 or 16/9 while others are configurable.
There are also “hybrid” cameras, which send an FPV stream and record HD video. However, they are less efficient than dedicated solutions, both for video return and HD recording.
The Video transmitter
It is commonly called VTx (for Video Transmitter or Video Tx). It is wired with the video stream filmed by the FPV camera. It then transmits a radio signal (most often in 5,8 GHz) to a video receiver connected to your FPV mask or FPV goggles.
The frequency on which a VTx transmits is determined by a band and a channel.
It is commonly called VTx (for Video Transmitter or Video Tx). It is wired with the video stream filmed by the FPV
In general, we use the “Raceband”, which can distribute the channels over frequencies that are far apart to allow several people to fly without interfering with each other. The power of the vTx is also adjustable even if you are not supposed to exceed 25mW.
Most recent transmitters offer a “Smart Audio” or “IRC Tramp” feature to set up remotely the channels and power of your VTX.
A VTX requires an antenna to transmit. Be careful: never turn on a VTX without an antenna connected, or it will burn out. Two types of connectors are used to put antennas on the VTX: the µ.Fl and the MMCX.
The VTX Antenna
There are many types of antennas. Some are omnidirectional, others directional. On our FPV drones, we use omnidirectional ones; as the quad is in constant motion, it must transmit in all directions.
The antennas are polarized, either RHCP (Right-Hand Circularly Polarized) or LHCP (Left-Hand Circularly Polarized). You will have to check and match the type of polarization between the transmitter and the receiver. There are also linearly polarized antennas, mainly used on Tiny FPV drones.
Finally, a word about connectors: some antennas have a connector directly on board which is suitable for VTX (µ.FL or MMCX), but often an intermediate connector in SMA or RP-SMA format is used. When choosing your antennas, always make sure which connector you need. You will not be able to screw an SMA antenna onto an RP-SMA socket.
The radio receiver
Usually abbreviated as “Rx” (for Receiver), the Receiver receives the commands sent by the radio controller and transfers them to the flight controller. Some models also support telemetry, which allows the drone and the radio to exchange other information in both directions (e.g., sending back to the radio the state of the LiPo or the GPS position).
The Rx uses a protocol to exchange with the quad. The most common ones are SBUS, IBUS, F.Port, or Crossfire (CRSF), depending on the solutions chosen.
The firmware of the Rx can be updated, often through the radio control, wired or wireless, to support new features.
The Flight controller
Finally, we can talk about the flight controller or “FC” for Flight Controller. We have saved it for last because it is at the heart of all the components seen previously. It is the brain of this little world, a real tiny computer.
It embeds a microprocessor or MPU (F4, F7, or H7 generation for the most recent) and sensors (gyroscope, accelerometer, voltage sensor, etc.). It offers inputs/outputs (UARTs), accessible thanks to soldering pads to connect the rest of the quads’ peripherals (ESCs, Rx, vTx, etc.).
Often, it is the FC that adds the OSD on top of the camera’s video stream. The OSD allows you to see a lot of useful information (such as the status of the lipos, the flight duration, the quality of the radio signal, etc.) in the video return.
It comes in the form of an electronic card, in 20×20 or 30×30 format (and even 16×16 or 26×26 for the nano quads). It is called a ” stack ” when the FC is sold with a 4-in-1 ESC.
Note the existence of “AiO” (All-In-One) FCs, which integrate several functionalities :
- PDB, for the use of separate ESCs.
- ESCs, are more and more frequent for TinyWhoop or Toothpicks.
- The VTX and the Rx are sometimes also part of it.
To function, a Flight Controller relies on embedded software. As for the ESCs, we talk about firmware. The most widespread are Betaflight, KISS and Emuflight. Others are more “autonomous flight” oriented, as is the case for iNav.
This firmware has the heavy task of analyzing everything that happens in real-time to adapt the quad’s behavior to the orders received via the Rx. The firmware tells the ESCs how fast to run each motor.
Each FPV drone is different, and we can adjust parameters in the firmware to provide better flying sensations.
These adjustments are made via parameters: PIDs (Proportional, Integral, Derivative) and filters (which aim to remove parasites from the different signals). This subject is far beyond the scope of this article, but note that it exists, and one day or another, you will be more interested in it.
It is a small component often underestimated. Its role is to absorb voltage peaks to protect the electronics and filter the noise generated by the ESCs.
It is used to limit the disturbances in the analog video return. But we must not forget its “invisible” protection and filtering effects; for example, the gyro is very sensitive, and the cleaner the input signal, the better the flight controller will be able to do its job (less software filtering to apply).
The ideal placement of a capacitor is as close as possible to the electronic noise source and thus to the ESCs. For 4-in-1 ESCs, we will solder it to the battery supply pads used to connect the LiPo. For separate ESCs, the ideal is to put a small capacitor on each ESC. A capacitor is soldered in parallel to the power supply on the “+” and “-“, taking care to respect the polarity.
A capacitor is defined by its capacity (in µF) and limit voltage. The last point, it is imperative to use a ” LOW ESR ” capacitor (low series resistance).
We have seen the essential. It is still possible to add other parts to the FPV Drones, for example, a buzzer (to find it more easily), a GPS, LEDs, etc.