ACCESS

ACCESS (Advanced Communication Control, Elevated Spread Spectrum) is the radio protocol FrSky introduced in 2019 as successor of its ACCST protocol. It is supported by the ISRM module of the Taranis X9D Plus SE 2019 and by ACCESS receivers such as the R-XSR with ACCESS firmware. Before an ACCESS receiver can be bound it needs to be registered with the transmitter.

Analog

In the context of FPV analog refers to the classic way of transmitting the live video from the FPV camera over a VTX, usually in the 5.8 GHz band using the PAL or NTSC standard. Analog video has a very low latency and its image quality degrades gradually with increasing distance or obstacles instead of freezing, which is why it is popular for racing. Digital HD systems provide a much sharper image in exchange for a slightly higher latency.

Battery

Batteries in a FPV drone are connected to the PDB to power the components. For drones LiPo batteries are used because of their high energy density, which makes them weigh less and therefore improve the flight time.

A battery has two important measures. Its capacity and cell count that specify their voltage level.

Different LiPo battery packs are made up of individual cells with one cell having 3.7V. Typical cell counts are defined as:

Cell count Voltage
2S 7.4 V
3S 11.1 V
4S 14.8 V

BEC

Abbreviation for Battery Elimination Circuit which describes ESCs that provide a portion of battery power (which the ESC is connected with) over their communication cable (red cable of the servo connector) to other devices such as a receiver and servos attached to the receiver.

BetaFlight

The BetaFlight open source Flight Controller firmware project (found on GitHub) provides firmwares for FCs. To configure and flash a firmware onto a Flight Controller we use the BetaFlight Configurator.

BetaFlight is a fork of the CleanFlight project, which is considered less experimental. However, modern Flight Controllers are supported mostly by BetaFlight.

BetaFlight Configurator

Part of the BetaFlight open source Flight Controllers firmware project. It is a cross platform (runs on most operating systems, Windows, Linux, MacOS) configuration tool for the BetaFlight firmware. It has since been renamed to the Betaflight App, which runs in Chromium-based browsers.

Bind

Bind is referred to binding a receiver with a transmitter.

BLHeli

Firmware for ESCs that is used to process the input data from a Flight Controller and translate that into suitable control commands for the motor. Although the firmware was originally developed for helicopters it is also used for multicopters. Another commonly used firmware for ESCs is called SimonK. Development of the 32-bit version BLHeli_32 ended in June 2024. Its open source successors are AM32 for 32-bit ESCs and Bluejay for 8-bit BLHeli_S ESCs.

CFK

German abbreviation for “Carbonfaserverstärkter Kunststoff”, which is known as carbon fiber reinforced polymer (CFRP) in English. Because of its high stiffness and low weight it is the most common material for FPV frames and propellers.

CleanFlight

Open source Flight Controller firmware (found on GitHub), which started as a fork of the BaseFlight project. BetaFlight was in turn forked from CleanFlight.

DFU

DFU stands for “Device Firmware Update” which is a mode of a Flight Controller device that is required to flash a new Firmware onto a FC. It depends on the FC board how to get the device into the DFU mode. Either you need to short the BL or BOOT pads (or press and hold the BOOT tactile button if your FC board has one) while plugging the USB into the Flight Controller board.

EdgeTX

Open source firmware for RC transmitters, started in 2021 as a fork of OpenTX. Most radios ship with it today. It is configured on the radio, with EdgeTX Companion or with the browser-based EdgeTX Buddy. Reference: EdgeTX.

ESC

The Electronic Speed Controller (ESC) is connected to the PDB and controls the speed of a motor by adjusting its rpm (revolutions per minute). A quadcopter uses four ESCs which can be part of the Flight Controller. The input signal to an ESC comes from the Flight Controller, which tells the ESC at which speed a motor should run. More details are found on the ESC page.

EU LBT

EU LBT stands for European Union Listen Before Talk (or Transmit) and is a firmware version for receivers and transmitter modules, which is allowed in the geographical region of the EU. Another firmware version is the FCC version which can be used outside the EU. Reference: Brushless Whoop.

ExpressLRS

Open source RC link (ELRS) between transmitter and receiver on 2.4 GHz or 900 MHz. It uses LoRa modulation and small packets for long range and low latency, and has become the most common RC link in FPV. Reference: ExpressLRS.

FCC

Stands for Federal Communications Commission which regulates use of radio frequencies within the United States. Reference: Brushless Whoop.

Firmware

In the context of FPV a firmware is the software that runs on the Flight Controller. Other devices such as ESCs, receivers and transmitters run their own firmware too.

Flash

Flashing means to update a Software, also referred to as Firmware, that runs on a device, such as a Flight Controller board. The term “to flash” comes from the Flash storage component of a device where the Firmware is stored.

Flight Controller

Micro Controller board that contains input and output (I/O) pins and a processing unit (microchip), which runs a Flight Controller firmware. The Flight Controller acts as the brain of a drone. By processing sensor input signals the Flight Controller is used to compute output signals for external or internal ESCs to keep level flight. Other input signals are used to adjust the pose of the quad in the air such as the receiver and other internal or external sensors. A Flight Controller usually contains multiple internal sensors such as IMUs.

FPort

Rx protocol that acts as a communication interface between receiver and flight controller. FPort is developed by Betaflight’s developer team and FrSky for its receivers.

  • FPort combines SBUS and Smartport Telemetry into one single wire
    • Simplify cable management and soldering
    • Save a UART port because SBUS and Smartport take up two separate UART’s
  • FPort is an uninverted protocol, which should avoid doing “uninversion hacks” on F4 FC in future Frsky receivers
  • FPort is slightly faster than SBUS
  • RSSI works automatically (no need to pass through a channel)

References:

FPV

Abbreviation for first person view, where the live image from a flying quad is viewed through an analog video receiving system. This can be either a fpv goggle or monitor.

FPV Camera

Small and lightweight camera mounted at the front of the quad that captures the live image for the pilot. FPV cameras are optimized for low latency and quickly changing light conditions rather than for a high resolution. The video signal is sent to the VTX, which transmits it to the goggles. The quad in this project uses a RunCam Swift 2 (see components).

FrSky

FrSky is a Chinese company that manufactures modules for rc toys such as transmitters, receivers or Flight Controllers. Their transmitters and receivers are among the most common in the FPV scene. At their homepage https://www.frsky-rc.com/ you can see all the products and download manuals and firmware updates.

Goggle

Used to view the analog live image captured by the camera on the quad, which is transmitted with the video transmitter that sits also on the quad.

IMU

An inertial measurement unit (IMU) is a sensor that measures angular rates with a gyroscope and accelerations with an accelerometer. The Flight Controller uses these measurements to estimate and control the pose of the quad.

ISRM

Name of the internal transmitter module of FrSky’s 2019 radios such as the Taranis X9D Plus SE 2019. It supports the ACCESS protocol and the older ACCST D16 protocol, depending on the selected mode and firmware. How to update it is explained on the Taranis page.

LBT

LBT stands for Listen Before Talk or Listen Before Transmit and describes the version of a firmware for transmitters and receivers. The LBT version also referred to as EU LBT is the allowed version in the European Union. Most of the FrSky receivers and transmitters are sometimes referenced as EU or non EU or EU LBT and FCC.

Reference: Brushless Whoop.

LED

Light Emitting Diodes are used as visual guidance for a quad copter.

LiPo

Refers to a type of battery and is the abbreviation for __li__thium __po__lymer.

Motor

Quads use brushless DC motors that are driven by an ESC and spin the propellers. How they work and how to read their specifications is explained on the motor page.

OpenTX

Open source firmware for RC transmitters such as the Taranis X9D Plus. It is configured on the radio itself or with OpenTX Companion. Reference: OpenTX. OpenTX is no longer developed (its last release was in April 2022), most radios now run its fork EdgeTX.

OpenTX Companion

Desktop application for Windows, Linux and MacOS that is used to configure models and settings of an OpenTX radio, to back them up and to flash new OpenTX firmware onto the radio.

PDB

The Power Distribution Board (PDB) acts as the heart of an FPV quad. It is connected to the Battery and distributes its power to other components of the quad. The main components it is connected to are the ESCs to power the motors. A PDB usually has additional voltage outputs such as 5V and 12V to power sensors or LEDs.

Pose

The pose describes the position and orientation (attitude) of the quad in space. The orientation is commonly expressed with the roll, pitch and yaw angles.

PWM

Short for pulse width modulation.

Radio

The term radio is used for the transmitter device. It comes from the fact that radio frequency is used as a communication medium between the transmitter and receiver of rc.

RC

Short for radio controlled.

Receiver

The receiver (also referred to as Rx) is installed in the quad or radio controlled (rc) vehicle and communicates with the transmitter.

Redundancy

Describes a type of receiver which can be used in combination with other receivers of the same type to provide redundancy in case of a receiver failure.

Register

Registering is a step required by the ACCESS protocol before a receiver can be bound. During registration the receiver gets a name and stores the owner ID of the transmitter. The steps for the R-XSR are shown on the R-XSR page.

RPM

Abbreviation for revolutions per minute, which is the unit used for the rotational speed of a motor.

RSSI

Received Signal Strength Indicator. It indicates how good the radio link between transmitter and receiver is and is usually shown in the goggles or reported via telemetry to warn before the link is lost.

Rx

Short for receiver.

R-XSR

Redundancy receiver produced by FrSky. Its setup is explained on the R-XSR page.

SBUS

Serial bus protocol originally developed by Futaba and used by FrSky receivers to transmit up to 16 channels over a single wire to the Flight Controller. SBUS is an inverted serial signal, which is why some Flight Controllers need a dedicated or inverted UART for it.

Sensor

A sensor measures a physical quantity and provides it to the Flight Controller. Common sensors on a quad are the IMU (gyroscope and accelerometer), a barometer to measure altitude and a current sensor on the PDB to measure the current draw.

Servo

A servo is an actuator with position control used in RC models, for example to move control surfaces of a plane. Its three wire connector (signal, power and ground) is the standard connector for RC equipment such as receivers and ESCs.

SimonK

Firmware for ESCs that is used to process the input data from a Flight Controller and translate that into suitable control commands for the motor. This firmware was developed by Simon Kirby and its intended to be used in multicopters. Its source code can be found on Simon Kirby’s GitHub repository. Another commonly used firmware for ESCs is BLHeli.

SmartPort

SmartPort (S.Port) is FrSky’s bidirectional single wire protocol to transmit telemetry data from the Flight Controller and other sensors over the receiver to the transmitter. It is also used to flash firmware onto receivers. Like SBUS it is an inverted signal.

Taranis

Series of RC transmitters from FrSky running OpenTX. This project uses the Taranis X9D Plus SE 2019.

TBS

Team BlackSheep (TBS) is a manufacturer of FPV equipment such as the TBS Unify Pro video transmitters and the TBS Crossfire long range radio system.

Telemetry

Telemetry is data sent from the quad back to the pilot, such as battery voltage, current draw or RSSI. With SmartPort or FPort the receiver sends it to the transmitter, where it can be displayed or used for alarms. The setup is explained on the telemetry page.

Transmitter

Also known as radio is the radio controlled (rc) part that communicates with a receiver. The term Tx is commonly referred to transmitting units. Such units can be external or internal in transmitter devices. External devices can be swapped.

One of the most common manufacturers for FPV quad transmitters is FrSky.

Tx

Short for transmitter.

UBEC

If the electronic components in a copter should be powered independently of the ESCs or if only optocoupler ESCs are used, there exist other ways to power the flight controller and other electronic components such as LEDs: It’s possible to use an UBEC (Universal Battery Elimination Circuit). This device is connected to the battery and can be used to provide constant output voltage for electronic components.

VTX

The video transmitter (VTX) sends the live image of the FPV camera to the goggles, usually in the 5.8 GHz band. Its output power and channel can often be changed from the Flight Controller, for example with the TBS SmartAudio protocol of the TBS Unify Pro used in this project.

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