How to: FPV
This is part 2 of the ‘How to quadcopter’ series. You can find part 1 here.
In part 1, I covered how 2.4GHz radio systems are used to control drones. In this post, I’ll be looking at how pilots can control their multirotor beyond visual LOS (Line-of-Sight) through FPV (First Person View).
Let’s start with the camera. FPV cameras are designed to be small and lightweight so they can be easily mounted on drones or other vehicles. All contemporary racing drone frames have hardware designed to securely mount FPV cameras. These hold the camera securely inside of the drone’s frame to protect the lens in case of a crash. These camera mounts allow the pilot to position the camera at specific angles so that when the multirotor is flying at high speed with the frame tilted forward, the camera remains level in relation to the ground.
There are a few different specifications of FPV cameras that are very important to drone pilots: the sensor, size, latency and lens.
FPV cameras can have either CCD or CMOS sensors. CCD (Charged Coupled Device) sensors have lower susceptibility to vibration and can handle sudden changes in light more effectively (dynamic range). CMOS (Complementary Metal Oxide Semiconductor) sensors have become more capable than they once were, but their most interesting use is in low-light cameras, which are able to be used in very dark lighting conditions. The size of FPV cameras is standardised between camera and frame manufacturers, with companies such as Runcam producing cameras in three sizes: nano, micro and full size.
The latency of an FPV camera refers to the time it takes for the camera to output an image after light is captured by its sensor. Whilst this time is only measured in milliseconds, combined with the time taken for the the FPV radio system to send, receive and output it may be a significant amount of time, especially when you factor in the delay of the control radio as well.
The lens of an FPV camera determines the total FOV (Field of View) of the received image. This is measured by their focal length, in mm. The most common lens is 2.8mm, which translates to ~115°. Some people prefer to use wider lenses, and the most popular option is the 2.5mm GoPro Hero 1/2 lens, with a ~130° FOV, which uses the same M12 mounting method as full-size FPV cameras.
The TVL of a camera (TeleVision Lines) is how FPV cameras measure their resolution. More lines directly impacts the image quality of the camera. The sweet spot for current FPV solutions is 600 TVL, as this provides plenty of clarity to discern detail in the image without drastically increasing the image processing required by the camera, which would increase the overall latency of the system.
In order to send the video output from the FPV camera to the pilot, the signal must be transmitted from the multirotor. Currently, this is achieved via analogue radio transmitters (VTX). They are essentially the same as the radio modules found in the transmitters we looked at in Part 1. Digital systems such as the ones used in commercial products are not currently accessible enough to be used by the average hobbyist.
A mentioned previously, full-range (~1.5km) control systems use the 2.4GHz band, which strikes a good balance between antenna size and signal penetration (through obstacles). A decrease in the wavelength of a radio system results in a decrease in the antenna size needed, but also means the signal is more likely to be obstructed by trees, hills and buildings. Despite this, drones almost exclusively use the 5.8GHz band for their video link, as weight saving is a priority in all rotorcraft. This also moves the video transmission frequency further away from the control signal, reducing the likelihood of interference between the two.
To compensate for the reduced wavelength and increased data transmission size, FPV transmitters are much more powerful compared to their control counterparts. The FrSky Taranis represents the typical hobby-grade transmitter (TX), transmitting at a power of 100mW. On the other hand, the TeamBlackSeep (TBS) Unify Pro, representing the high-end of VTXs, transmits at up to 800mW -- useful for proximity flying.
It should be noted that the legal limit for FPV TXs is 25mW in the UK.
I referred to an ‘OSD’ in Part 1, when talking about flight controllers and their various integrated functions. An OSD (On Screen Display) is used inbetween the camera and the VTX, overlaying critical flight information into the transmitted video signal, such as battery voltage, flight time, direction to takeoff point and distance travelled from takeoff. This prevents the pilot from discharging the battery too much or from becoming disorientated, resulting in a safer flight.
Receiving the signal is handled by the VRX, and is not as instrumental in determining the range of the system. The only important factor, other than frequency and available 5.8GHz channels is the sensitivity of the module; this is something that is not worth considering if this is the first time you’ve heard of this term, as all modern VRXs are great for general use.
Something that is worth considering is diversity. This means that the receiver contains two separate RX modules, and automatically switches to the one with better signal at any given time. The best way to utilise this is to use two different types of antenna: one omnidirectional antenna and one directional antenna.
Antennas are designed to work specifically with one frequency band (2.4GHz, 5.8GHz etc). The connectors they use are either SMA or RP-SMA. SMA (Sub-Miniature Version A) and Reverse-Polarity SMA connectors are utilised due to the coaxial wire used by FPV antennas. When buying antennas, VTXs and VRXs, make sure the connector of the VRX/VTX matches the antenna’s connector that you have bought for each component.
There are multiple ways to view an FPV signal from the ground.
The cheapest method is through a small display, for instance the ones made for car back seats. These screens are designed to run off of car electrical systems (12V), meaning they can be powered using a 3S LiPo battery (11.1V). However, these displays often have a low resolution, but more importantly are almost impossible to use in bright sunlight. The preferred choice for most FPV pilots are FPV goggles. Goggles provide excellent light isolation due to their enclosed displays. However, the price of a good pair of FatShark goggles is definitely far too high for what you get. This is supposedly due to the fact that the tiny LCDs they use are not produced in large quantities by the manufacturer. On top of this, in order to add features like diversity, you must buy a seperate aftermarket module, further increasing the price of your ground station.
In part 1, I covered how 2.4GHz radio systems are used to control drones. In this post, I’ll be looking at how pilots can control their multirotor beyond visual LOS (Line-of-Sight) through FPV (First Person View).
Creating an image
Let’s start with the camera. FPV cameras are designed to be small and lightweight so they can be easily mounted on drones or other vehicles. All contemporary racing drone frames have hardware designed to securely mount FPV cameras. These hold the camera securely inside of the drone’s frame to protect the lens in case of a crash. These camera mounts allow the pilot to position the camera at specific angles so that when the multirotor is flying at high speed with the frame tilted forward, the camera remains level in relation to the ground.
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| Foxeer Arrow V3 |
There are a few different specifications of FPV cameras that are very important to drone pilots: the sensor, size, latency and lens.
FPV cameras can have either CCD or CMOS sensors. CCD (Charged Coupled Device) sensors have lower susceptibility to vibration and can handle sudden changes in light more effectively (dynamic range). CMOS (Complementary Metal Oxide Semiconductor) sensors have become more capable than they once were, but their most interesting use is in low-light cameras, which are able to be used in very dark lighting conditions. The size of FPV cameras is standardised between camera and frame manufacturers, with companies such as Runcam producing cameras in three sizes: nano, micro and full size.
The latency of an FPV camera refers to the time it takes for the camera to output an image after light is captured by its sensor. Whilst this time is only measured in milliseconds, combined with the time taken for the the FPV radio system to send, receive and output it may be a significant amount of time, especially when you factor in the delay of the control radio as well.
The lens of an FPV camera determines the total FOV (Field of View) of the received image. This is measured by their focal length, in mm. The most common lens is 2.8mm, which translates to ~115°. Some people prefer to use wider lenses, and the most popular option is the 2.5mm GoPro Hero 1/2 lens, with a ~130° FOV, which uses the same M12 mounting method as full-size FPV cameras.
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| 2.5mm lens |
The TVL of a camera (TeleVision Lines) is how FPV cameras measure their resolution. More lines directly impacts the image quality of the camera. The sweet spot for current FPV solutions is 600 TVL, as this provides plenty of clarity to discern detail in the image without drastically increasing the image processing required by the camera, which would increase the overall latency of the system.
Transmission
In order to send the video output from the FPV camera to the pilot, the signal must be transmitted from the multirotor. Currently, this is achieved via analogue radio transmitters (VTX). They are essentially the same as the radio modules found in the transmitters we looked at in Part 1. Digital systems such as the ones used in commercial products are not currently accessible enough to be used by the average hobbyist.
 |
| Eachine TX526 |
A mentioned previously, full-range (~1.5km) control systems use the 2.4GHz band, which strikes a good balance between antenna size and signal penetration (through obstacles). A decrease in the wavelength of a radio system results in a decrease in the antenna size needed, but also means the signal is more likely to be obstructed by trees, hills and buildings. Despite this, drones almost exclusively use the 5.8GHz band for their video link, as weight saving is a priority in all rotorcraft. This also moves the video transmission frequency further away from the control signal, reducing the likelihood of interference between the two.
To compensate for the reduced wavelength and increased data transmission size, FPV transmitters are much more powerful compared to their control counterparts. The FrSky Taranis represents the typical hobby-grade transmitter (TX), transmitting at a power of 100mW. On the other hand, the TeamBlackSeep (TBS) Unify Pro, representing the high-end of VTXs, transmits at up to 800mW -- useful for proximity flying.
It should be noted that the legal limit for FPV TXs is 25mW in the UK.
I referred to an ‘OSD’ in Part 1, when talking about flight controllers and their various integrated functions. An OSD (On Screen Display) is used inbetween the camera and the VTX, overlaying critical flight information into the transmitted video signal, such as battery voltage, flight time, direction to takeoff point and distance travelled from takeoff. This prevents the pilot from discharging the battery too much or from becoming disorientated, resulting in a safer flight.
Reception
Receiving the signal is handled by the VRX, and is not as instrumental in determining the range of the system. The only important factor, other than frequency and available 5.8GHz channels is the sensitivity of the module; this is something that is not worth considering if this is the first time you’ve heard of this term, as all modern VRXs are great for general use.
Something that is worth considering is diversity. This means that the receiver contains two separate RX modules, and automatically switches to the one with better signal at any given time. The best way to utilise this is to use two different types of antenna: one omnidirectional antenna and one directional antenna.
 |
| Eachine EV800D with diversity |
Antennas are designed to work specifically with one frequency band (2.4GHz, 5.8GHz etc). The connectors they use are either SMA or RP-SMA. SMA (Sub-Miniature Version A) and Reverse-Polarity SMA connectors are utilised due to the coaxial wire used by FPV antennas. When buying antennas, VTXs and VRXs, make sure the connector of the VRX/VTX matches the antenna’s connector that you have bought for each component.
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| Male SMA connector |
Some antennas are omnidirectional, and some are directional. This refers to their radiation pattern, which is either even in all directions or only covers one area respectively. This makes omnidirectional antennas especially suited to multirotors, whose flight range is limited by their short flight times. With FPV planes, directional antennas are often more useful, as they can fly for much longer and therefore further in a single direction. The combination of the two in diversity receivers results in both good close-range and long-range performance (albeit in one direction).
Directional antennas will usually have much greater gain, increasing range but decreasing spread. An antenna with 0dB of gain would have a torus-shaped radiation pattern.
The patch antenna is the most basic type of directional antenna, used extensively due in part to its low price to manufacture and low profile. It can be both linearly and circularly polarised. The helical is another circularly polarised directional antenna, usually with a slightly narrower spread due to their higher gain.
The monopole and dipole are almost always included with FPV systems, with the former on micro-sized transmitters and the latter on standard-sized systems. The cloverleaf and skew-planar antennas are similar in their construction, but differ in the number of ‘lobes’ they have, 3 and 4 respectively. As they are very delicate, when used on the VTX side they are contained within a plastic casing.
For optimal performance and a stable signal, circularly-polarised and linearly-polarised antennas should be used only with antennas of the same type to prevent cross polarisation.
Directional antennas
Directional antennas will usually have much greater gain, increasing range but decreasing spread. An antenna with 0dB of gain would have a torus-shaped radiation pattern.
The patch antenna is the most basic type of directional antenna, used extensively due in part to its low price to manufacture and low profile. It can be both linearly and circularly polarised. The helical is another circularly polarised directional antenna, usually with a slightly narrower spread due to their higher gain.
Omni-directional antennas
The monopole and dipole are almost always included with FPV systems, with the former on micro-sized transmitters and the latter on standard-sized systems. The cloverleaf and skew-planar antennas are similar in their construction, but differ in the number of ‘lobes’ they have, 3 and 4 respectively. As they are very delicate, when used on the VTX side they are contained within a plastic casing.
For optimal performance and a stable signal, circularly-polarised and linearly-polarised antennas should be used only with antennas of the same type to prevent cross polarisation.
 |
| A few types of FPV antenna |
Viewing
There are multiple ways to view an FPV signal from the ground.
The cheapest method is through a small display, for instance the ones made for car back seats. These screens are designed to run off of car electrical systems (12V), meaning they can be powered using a 3S LiPo battery (11.1V). However, these displays often have a low resolution, but more importantly are almost impossible to use in bright sunlight. The preferred choice for most FPV pilots are FPV goggles. Goggles provide excellent light isolation due to their enclosed displays. However, the price of a good pair of FatShark goggles is definitely far too high for what you get. This is supposedly due to the fact that the tiny LCDs they use are not produced in large quantities by the manufacturer. On top of this, in order to add features like diversity, you must buy a seperate aftermarket module, further increasing the price of your ground station.
An alternative method of designing FPV goggles utilises a single, large LCD, which dramatically cuts the cost of the goggles, whilst maintaining all the benefits of FatShark style goggles: immersion, light isolation and the ability to have a self-contained system (battery, display, receivers). Goggles such as the Eachine EV800D incorporate a large range of usable frequencies (40CH), diversity, auto-scanning and even a DVR. The main drawback of these ‘boxed’ goggles is their size, which is a couple of times larger than a FatShark pair.
The resolution and ratio of your display is also important. A low resolution means you’ll be able to see individual pixels more easily, reducing the overall clarity of the display, and vice versa. The aspect ratio of the display is also a key factor. You may be familiar with the standard widescreen format of 16:9, but a majority of FPV systems use 4:3 (like early iPhone models). There are arguments for both ratios, but for multirotors, whose flight patterns involve staying low to the ground, 4:3 is objectively the better choice as it offers more vertical pixels meaning the aircraft is still controllable at a greater tilt.
So that’s FPV covered. By now you should have a great understanding of how multirotors work, and how you could go about building your own.
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| 'Snow' on single monitor goggles |
The resolution and ratio of your display is also important. A low resolution means you’ll be able to see individual pixels more easily, reducing the overall clarity of the display, and vice versa. The aspect ratio of the display is also a key factor. You may be familiar with the standard widescreen format of 16:9, but a majority of FPV systems use 4:3 (like early iPhone models). There are arguments for both ratios, but for multirotors, whose flight patterns involve staying low to the ground, 4:3 is objectively the better choice as it offers more vertical pixels meaning the aircraft is still controllable at a greater tilt.
So that’s FPV covered. By now you should have a great understanding of how multirotors work, and how you could go about building your own.
My upcoming posts will depart from the topic of multirotors, but it's something I will definitely return to in the future. Stay tuned!
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To keep up-to-date on this and future projects, join the mailing list by pressing the “Subscribe” button at the top of the page.
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