Lesson 7. First Person View (FPV)

Content

Introduction

The first six lessons cover the design considerations behind building a custom multi-engine UAV/Drone. Lesson 7 does not cover assembly aspects, but describes a number of additional accessories / devices used to implement first-person flight (FPV) and long-range control. This article is more focused on the application of radio control in the “field”; as opposed to flying indoors or in areas where power outlets can provide power. Please note that this tutorial only covers a very small part of the information needed to properly understand FPV/Long Range Systems and is intended primarily to introduce the reader to the concepts, terms, products and principles behind FPV and long range drone control.

First Person View (FPV)

First Person View (FPV – First Person View) is one of the main driving forces behind the rapidly growing popularity of multi-engine UAVs, allowing you to get a completely different perspective (“bird’s eye view”) of our planet and the very feeling of flying. While adding a camera to a drone is nothing new, the relative ease of operation, low price, and wide range of drones make it easy to buy or build an unmanned aerial vehicle with a camera.

First Person View (FPV) is currently implemented through a tandem pre-installed on the aircraft, consisting of an FPV camera and a video transmitter, which allows real-time video to be sent to the pilot or assistant. Please note that the market offers ready-made or semi-finished FPV systems, where in turn, ready-made FPV systems provide the user with confidence that all its elements are compatible with each other.

Video camera

• Almost any video camera that has the ability to connect to a video transmitter can be used for FPV flight, however it is important to consider weight as multi-engine UAVs constantly struggle with gravity and do not have the advantage of a winged aircraft to provide additional lift.
• Camcorders come in a wide variety of shapes and sizes, and can have varying potential in video quality, yet there are currently very few adapted specifically for UAVs. Due to these size, weight, and performance limitations, most cameras used in multi-motor FPV systems come from “action cams” as well as video surveillance and security industry applications (such as hidden cameras).
• Large cameras such as DSLRs or large camcorders are commonly used by professionals, but due to their weight, the drone required tends to be quite large.
• Some camcorders can be powered directly from a 5V power supply (useful since most flight controllers also operate at 5V, powered by the BEC), while others may require 12V or even their own built-in rechargeable battery.
• The most popular camera currently used on multi-engine UAVs is the GoPro. This is due to their durability, small size, high video/photo quality, built-in battery, wide range of accessories and worldwide availability. GoPro cameras also have a USB output that can be used to transfer video, and some even have a built-in WiFi module to transfer video over short distances.
• Given the success of GoPro, many other manufacturers have created their own similar lines of sports/action cameras, but their features, price, and quality vary. Please note that if you require 3D video, you will need two cameras and a video transmitter capable of transmitting two signals.

suspension

The gimbal system includes a mechanical frame, two or more motors (usually up to three for pan, tilt, and roll), as well as sensors and electronics. The camera is mounted so that the motors do not have to provide an angular force (torque) to keep the camera at a fixed angle (“balanced”).

The axes in question allow you to pan, tilt, or rotate the camera. A 1-axis system that does not have its own sensor can be considered a pan or tilt system. The most popular design involves the installation of two motors (usually BLDC motors specially designed for use with gimbals) that control the pan and tilt of the camera. Therefore, the camera is always facing towards the front of the drone, which also ensures that the pilot is not disoriented if the camera is facing one direction while the front of the drone is facing the other.

The 3-axis gimbal adds panning (left and right) and is most useful in tandem with two operators, where one person controls the drone and the other can independently control the camera. In this two-person configuration, a second (fixed) FPV camera for the pilot can also be used. As a rule, there is one of two types of cardan systems:

Brushless gimbal

• Brushless Direct Current Motors (BLDCs) or Permanent Magnet Synchronous Motors (PMSMs) or BLDC motors provide fast response with minimal vibration but require a separate (and dedicated) brushless DC controller.
• To automatically level the camera, an inertial measurement unit (IMU) consisting of an accelerometer and a gyroscope is installed somewhere around the camera (usually under its mount), so that the position of the camera (relative to the ground) can be tracked. The unit’s readings are sent to a separate DC brushless controller board (often mounted directly above the gimbal), which rotates the motors so that the camera position remains in a certain orientation despite any movement of the drone.
• The controller board itself includes an embedded microcontroller. A brushless DC gimbal controller can usually be connected directly to a channel on the receiver (unlike a flight controller), as it responds to changes in camera orientation, not UAV orientation, and is therefore independent of the flight controller.
• Note that because the GoPro is a popular action camera, most brushless gimbals are designed to be used with one or more GoPro models (based on GoPro size, center of gravity, camera location, etc.). You will also notice that BLDC gimbals almost always have damping which minimizes the vibration transmitted from the drone to the camera.

RC servo gimbal

• At the heart of an RC servo gimbal, a servo drive typically offers slower response times compared to brushless gimbals and excessive vibration. At the same time, servos are much cheaper than brushless ones, and 3-pin servos in most cases can be connected directly to the flight controller, which allows you to use the built-in PC – IMU, to determine the level relative to the ground, and then move the servos.

Video transmitter (VTX)

Currently, few flight controllers (with the exception of ready-to-run mass consumer UAVs) have a built-in video transmitter, which means that a separate VTX retrofit is usually required. Video transmitters used in the drone hobby are currently popular because they are light and small. Other 3rd party video transmitters can be used, but there are some important considerations regarding the power connection (may need to be adjusted if the device only accepts power from the “Barrel” connector) and input voltage; If the video device is running at a voltage that is not on board your build where, you may need additional electronics such as a voltage regulator. Video transmitters not related to the drone hobby are rarely satisfactory in terms of weight or size, and are usually enclosed in a protective case (and sometimes, unnecessarily heavy).

Video transmitter power

Video transmitters are usually rated for a certain power output, but it should not be assumed that anyone can use any power rating available on the market. Wireless frequencies and power are closely monitored and regulated, so it is highly recommended that you familiarize yourself with the wireless regulations of the country where you are located.

The power that a video transmitter consumes directly affects the maximum range of its signals. In North America, a wireless transmitter that consumes more than a certain amount of power (in Watts) requires the operator to have a Ham Radio Operator (HAM) license. For example, in Canada, a long range FPV operator is usually required to pass at least a “Basic Amateur Radio Proficiency Test” in order to operate at the power required for long range wireless applications.

If you are not qualified, it is highly recommended to use a video transmitter of less than 200mW to avoid the risk of lawsuits (authorities may contact you if your signal interferes with other wireless signals).

Power for the video transmitter is usually supplied by the BEC from one of the ESCs, which also powers the rest of the electronics. If you suspect that all electronics are drawing more current than a single BEC can provide, you can use the BEC from the second ESC to power the VTX. It is not recommended to use a separate battery to power the video transmitter.

VTX Frequencies/Channels

Most video transmitters operate at one of the frequencies listed below. Note that since you will probably already be using standard control equipment that operates at a certain frequency, it is a good idea to select a video transmitter so that their frequencies do not match. For example, if your remote control operates at 2.4 GHz, you should look for a video transmitter with an operating frequency: 900 MHz, 1.2 GHz or 5.8 GHz.

900MHz (0.9GHz)

• Low frequency signal penetrates walls and trees more easily
• DIY antennas are easy to make because low frequencies mean big antennas.
• Image quality is not as good as 5.8GHz
• May have a negative effect on GPS receivers
• Considered “old” technology
• Overall, best for mid-range

1.2GHz (from 1.2 to 1.3GHz)

• Used for long range FPV flights as it offers good range
• Many different antennas on the market
• The frequency is typically used by many other devices
• Walls and obstacles have more impact than lower frequency
• Medium/long range

2.4GHz (from 2.3 to 2.4GHz)

• Used for long distance FPV with few obstacles
• One of the most widely used frequencies for wireless devices
• Many accessories available (antennas, transmitters, etc.)
• Do not use near RC transmitters operating in parallel on the same frequency or other devices that may cause interference.
• May work with other frequencies, but will not be covered in this section.

5.8GHz

• Great for short range applications
• Walls and other obstacles have a significant effect on range
• Antennas small/compact
• Best suited for FPV in drone racing

As you may have noticed, many common wireless devices operate at 2.4GHz (wireless routers, cordless phones, Bluetooth, garage door openers, etc.). This is largely due to the fact that state regulations from the Federal Communications Commission have determined that the band around this band does not require a license to operate; the same for 900MHz, 1.2GHz and 5.8GHz (within certain power range). The unlicensed frequency range includes the so-called free ISM range (from the English Industrial, Scientific, Medical: industrial, scientific and medical range), occupies the frequency band: from 2400 to 2483.5 MHz in the USA and Europe and from 2471 to 2497 MHz in Japan. This means that any consumer can purchase a wireless device that operates on one of these frequencies without having to worry about regulations or guidelines. More information about the amateur radio frequency allocation can be found on Wikipedia.

Video transmitter connectors

Not all video transmitters have the same connectors, so it is important to know which connector is installed in the selected camera, and also to see if it is possible to connect and work with the selected video transmitter. The most popular connectors are composite, mini/micro USB and 0.1-inch connectors (analogue). There are a number of adapters/converters on the market, for example: 0.1″ FPV Tx connector – miniUSB for use with a GoPro camera, which greatly simplifies the use of such products.

Some video transmitters may also have an audio input, however in most cases the noise generated by the power plant will drown out any sound you are hoping to capture. If you need sound, be sure to position the mic as far away from the motors as possible (it will take a lot of testing to find the max. optimum location) and choose a compatible receiver.

Video transmitter antenna

Video transmitter antennas used on drones tend to be either “Duck” or “Whip”. Duck antennas are the most common and have the advantage of being omnidirectional, compact, inexpensive, and remain stationary during flight due to their small profile.

Antenna selection must match the frequency of the video transmitter. Higher frequencies require smaller antennas, but transmitted signals have more difficulty passing through obstacles. Low frequencies are less susceptible to interference, but require large/long antennas. A directional antenna is not very commonly used for video transmission, since the UAV can actually be in any orientation in three-dimensional space. Ideally, the antenna should be located somewhere on the UAV where there are no sources of other wireless signals or electrical interference.

Video receiver (VRX)

The video receiver tends to be slightly (physically) larger and heavier than the video transmitter because the receiver is usually stationary (connected to the screen) while the transmitter is mounted on the drone and as such should be small and light. To save space, some LCD manufacturers include standard frequency wireless receivers in their displays.

Many FPV enthusiasts attach Clover Leaf or Pinwheel antennas to their FPV goggles, which allows them to point their head in the direction of the drone and thereby achieve the strongest possible signal. Some manufacturers of FPV goggles have also embraced this trend by including a wireless video receiver and antenna in their goggles.

Obviously, the frequency at which the video receiver operates must match the frequency of the transmitter. Some receiver models, however, offer a wide selection of channels (one at a time), making them compatible with a variety of video transmitters. The video receiver output tends to be either composite (the most common) or HDMI. What to connect to the output (video display) is up to you, and some options are described below. Powering the receiver in the field always involves the use of a battery that either provides an output voltage that matches the operating voltage of the receiver, or a battery that is connected to a voltage regulator to supply the required voltage. Please note that there are no “long range” video receivers, since the signal range depends on the power of the transmitter and the right antenna.

Video receiver antenna

Antennas used on video receivers can be omnidirectional (capable of receiving a signal from any direction) or directional. The most common antennas you’ll see on a video receiver are: Duck antenna, Cloverleaf/Pinwheel or, in rare cases, directional (eg “Yagi”). A directional antenna will only be relevant if the UAV will fly in a certain direction in relation to the operator, and the drone will always be “in front” of the antenna in order not to lose the signal. Situations may include examining a specific area (such as a field) or an area that is at a distance from the operator.

video display

LCD monitor (LCD monitor)

• When considering an LCD monitor, it is important to know the difference between a desktop/computer LCD monitor or LCD TV and one that is designed to be portable. A TV/computer monitor almost always has a power connector that is compatible with a standard computer power cord (takes AC power directly), making it very difficult to use with a battery. The LCD/OLED display, which should be more portable, often draws DC current and requires an external transformer to connect to the mains (A/C).
• The size, refresh rate, and display quality of displays used for FPV applications range from small monitors with grainy images that update several times per second, to large displays that, when combined with the right video transmitter and receiver, display large HD images without any obvious delays. Keep in mind that any 2D display you choose must be connected to a power source and installed, either inside the UAV base station (described below) or by mounting the FPV monitor on the control equipment.

fpv goggles

• 2D glasses are widely used in FPV due to their more affordable price, compatibility with a single video source (from a single video camera), and ease of use with an external battery. Some models include a video receiver; kits come with a camera, video transmitter, FPV goggles (with built-in video receiver) and an external battery, as well as both antennas.
• The video quality offered by inexpensive FPV goggles can be quite low, so if budget matters, consider that you can get a better experience with a larger LCD monitor for the same price as FPV goggles.

head tracking

• Head tracking is essentially the same as motion tracking, namely measuring 3D orientation/angles as opposed to linear motion. The sensor complex consists of MEMS accelerometer chips, gyroscopes or inertial measurement units (IMUs). Sensors are installed (or built into) the FPV/VR goggles and send data to the microcontroller to interpret the sensor data as angles, which then sends the data, either via the control hardware (for higher end models) or via a separate wireless transmitter. The ideal head tracking system is compatible with the transmitter, so angles can be sent with the transmitter on two free RC channels.

3D/Virtual Reality

• Occulus Rift, Samsung Gear, Morpheus, smartphone-based VR glasses, and a host of other head-mounted 3D/VR displays can be adapted for use with drones. While these devices are usually made for 3D PC/console games or as an alternative to a TV, these devices are natively 3D compatible and often have built-in head tracking sensors, becoming more and more interesting to the FPV drone community.

smart devices

• Smartphones, tablets or laptops can be used to display live video. Their batteries are built-in, and the devices themselves are lightweight. The difficulty in using smart devices is that most receivers are not designed to receive video from a wireless video receiver (one of two wired or wireless). A laptop or tablet with a built-in or USB video card can receive normal composite video. A smartphone currently works best with video sent over Wi-Fi (from a Wi-Fi camera to a Wi-Fi dongle). Using the GoPro’s Wi-Fi video signal and mobile app is one of the easiest ways to implement FPV, but it’s worth noting that the camera’s Wi-Fi signal range is very limited (10-20 meters). Since smartphones are so widespread and drones are all the rage, manufacturers regularly release new products that they can capitalize on, so think carefully before making a decision.

On Screen Display (OSD)

• The On Screen Display (OSD) allows the pilot to see various sensory data sent from the aircraft. One of the easiest ways to display data on the screen is to use a camera with an analog output and place a screen board between the camera output and the video transmitter. The OSD adapter board has inputs for various sensors and will overlay the data on the video, so the pilot will receive video with the telemetry data already overlaid.

Distance considerations

• As you have already noticed, long distance operation depends mainly on the power of the transmitter (control equipment, as well as video, if applicable). Usually RC transmitters include an RF system consisting of joysticks and switches, electronics and an RF transmitter, and less expensive RC elements, this system is almost always a single unit. Higher end models often have an RF module, which can be seen as a box on the back of the control equipment. In North America, it is also a legal requirement that the UAV stay within the pilot’s line of sight (for information). However, laws change, so it’s best to seek advice before attempting drone operations over long distances.

Food

UAV/Drone

Your UAV/Drone is made up of many different parts, each requiring a different voltage. The most common electronics you will find in an FPV or long range drone include:

1. Engines: Most mid-sized UAV motors typically operate at 11.1V or 14.8V.
2. Flight controller, receiver, GPS: ideally they should be powered by the BEC from one of the ESCs.
3. Head tracking receiver: it will also work from BEC.
4. Servo suspension: The gimbal servo system can be powered by one of the BECs on the ESC and run at 5V.
5. BLDC suspension: Some BLDC gimbals can be connected to the main battery charging socket, while others may require a certain voltage. Check the specifications of the gimbal you are buying.
6. Camera: Cameras used for FPV flight tend to run at 5V (from the BEC) or 12V (from the main battery). Most action cameras have their own built-in battery.
7. Video transmitter: Most operate at 5V and can be powered by BEC.
8. Additional electronics (lighting, parachute, etc.): 5V.

It is recommended that the drone has only one main battery, and you should consider using a 11.1V or 14.8V battery on a medium sized drone. If more than one ESC doesn’t have a BEC, you’ll need an external 5V voltage regulator to power the electronics, and make sure it can provide enough current for everything.

Pilot

While the average drone user only needs to worry about the performance of the control gear, the pilot of a full-fledged FPV setup may end up carrying large batteries, and a variety of additional equipment.

1. Portable control equipment: Most remotes are powered by an “AA” battery (4 x AA or 8 x AA) by default, but FPV may require external battery power.
2. Optional RF Transmitter: If you are not using the RF Transmitter/Receiver that came with the remote control, the higher end models usually have a power outlet that you can connect this module to. In addition, you can power it with an external battery that powers the remote control.
3. Head tracking receiver: Usually this unit can be powered by 5V.
4. Video receiver: Most require 12V, but often have a fairly wide input voltage range. More often than not, the receiver comes with an AC adapter that you won’t be using in the field. Check the input voltage ranges to see if you can use the same voltage to power the transmitter and receiver (eg 7.4V or 12V).
5. Video display: Be sure to select a portable LCD display with a “Barrel” connector, which will allow you to use a battery pack for input. FPV goggles usually also have a barrel connector, but be sure to check. The most common voltage for portable LCDs is 12V, which may not be the best for other devices.
6. Antenna tracker: Described below. This motorized device often consists of radio controlled servo motors, a microcontroller and additional sensors/electronics. There are very few commercial systems available for the hobby drone market, so if you are designing and building such a system, you will need to develop a power setup.

Base station

As stated above, there is a lot of equipment that the pilot needs to carry and power that can be very bulky. Base stations are often used to relieve the operator of this burden/confusion and may consist of any number of different equipment and compartments listed below. It is not difficult to imagine that the outcome of the flight preparation depends on how well the base station is assembled, the wiring harnesses connecting all these devices together.

The base station may include:

• The main battery, possibly used to power the LCD monitor and/or FPV goggles, and possibly the video receiver.
• Auxiliary battery for transmitter and/or video receiver.
• Mount for LCD monitor and/or place for FPV goggles.
• Mount for video receiver.
• Storage space for control equipment.
• Long range antenna mount (or space for a portable directional antenna)
• Space for a charger for the main battery(s).
• A place for spare parts for the drone (propellers, motors, batteries, frame elements).

A “base station” is not necessarily a commercially manufactured product that can easily be used with any unmanned application, on the contrary, it can be designed and built by an amateur pilot himself. Usually building a base station starts with choosing a sturdy carrying case (like the Pelican or Nanuk), although a hard-framed backpack can also be used/adapted. A tripod is often used to mount the antenna higher off the ground.

Antenna tracker

Antenna tracker is an electromechanical device that tracks the position of the drone in three-dimensional space using GPS coordinates, and knowing the location of the GPS tracker, directs the antenna towards the drone. Antenna trackers are commonly used on long range missions and there aren’t many commercial products on the market. The tracker consists of a GPS receiver, a compass (and sometimes an IMU), a microcontroller, a data receiver (to receive the drone’s GPS coordinates), one pan and one tilt motor, a mechanical frame, a directional antenna, and a rechargeable battery. To reduce the negative impact of obstacles, antenna tracker systems are raised above the ground using a tripod.