Speak FPV

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Acro

Manual flight mode: the drone holds the angle you give it. The standard for freestyle and racing.

AIO

All-in-one: flight controller and ESC on a single board. Common on small drones.

Air mode

Feature that keeps control of the drone even when the throttle is at zero.

Angle

Self-levelling mode: the drone levels itself when you let go of the sticks.

AUW

All-Up Weight: total weight of the drone with the battery.

BEC

Voltage regulator that powers the camera, VTX or receiver.

Blackbox

Flight data log for analysis and tuning.

BNF

Bind-N-Fly: built drone with a receiver; you just need to bind it.

C (C rating)

Indicates a battery’s maximum current: capacity × C.

Cinewhoop

Small drone with prop guards, designed for filming.

Critical damping

The ideal PID response: it reaches the setpoint as fast as it can without overshooting or bouncing.

CRSF

Communication protocol between receiver and flight controller used by ELRS.

Cutoff frequency

Point at which a filter already attenuates 3 dB. The lower it is, the more noise it removes and the more delay it adds.

Deadcat

Frame with the front arms spread out so the props don’t show up in the image.

Decibel (dB)

Unit for comparing signals: −3 dB leaves 71 %, −6 dB half and −20 dB 10 %.

DFU

Flight controller mode for updating the firmware when it doesn’t respond.

Dive

Vertical plunge, usually from the top of a building or a mountain.

DShot

Digital protocol between flight controller and ESC.

DVR

Video recording in the goggles.

Dynamic D

Feature that uses a low D in calm flight and raises it towards a maximum on sharp stick inputs and in propwash.

ELRS

ExpressLRS: open-source radio system, the current standard.

ESC

Electronic speed controller that controls the speed of each motor.

Expo

Softens the drone’s response near the centre of the sticks.

Failsafe

What the drone does when it loses the radio signal. By default, stop the motors.

FC

Flight controller: the drone’s brain.

Feedforward

Part of the control loop that reacts directly to stick movement.

FPV

First Person View: flying while seeing what the drone’s camera sees.

Fresnel zone

Rugby-ball-shaped volume between the radio and the drone that must be clear of obstacles for the signal to get through well. The further away, the fatter it is.

Gap

Narrow opening you fly through: between branches, windows or doors.

GPS Rescue

Feature that brings the drone back towards the take-off point if it loses signal.

Gyro

Gyroscope: the sensor that measures how the drone rotates. Its data is what the PID corrects.

Gyroflow

Free program that stabilises video using gyro data from the camera or from the Blackbox log.

Horizon

Mixed mode: self-levelling near the centre and acrobatic at the ends.

I-term relax

Feature that stops the I term building up during flips and causing slow bounce-backs when they finish.

Intermodulation (IMD)

Interference that appears when two VTXs transmit at the same time: they combine and create ghost signals on other channels (2·f1 − f2).

IR

Internal resistance of the battery. The lower, the better. Note it in the battery logbook to see how it ages.

KV

Revolutions per minute per volt of a motor, unloaded.

Lap timing

System that detects when a drone crosses the finish line by reading its VTX signal, to count laps and run races.

LiHV

LiPo that charges up to 4.35 V per cell.

Link budget

Power accounting for a radio link: what you transmit, minus what is lost along the way, compared with what the receiver needs. The difference is the margin.

LiPo

Lithium polymer battery, the most widely used in FPV.

LOS

Line of Sight: flying while looking straight at the drone, without goggles.

Low-pass (LPF)

Filter that lets the drone’s slow movement through and attenuates high-frequency noise.

LQ

Link Quality: percentage of radio packets received.

Notch

Filter that cuts a narrow band of frequencies with little delay. The dynamic one finds the noise peak by itself.

Open source

Software or hardware whose code or designs are published so anyone can study, modify and share them. Betaflight, ExpressLRS and EdgeTX are open source.

OSD

Data overlaid on the image: voltage, time, signal.

Overshoot

When the gyro goes past the setpoint and has to come back. You see and feel it as a bounce at the end of tricks.

P/D balance

Ratio between P and D (P ÷ D). Each drone has one that suits it; when you raise the gains, P and D go up together to keep it.

Phase delay

Lag that any filter adds to the signal. The delays of all the filters add up.

PID

Algorithm that corrects the drone’s attitude. Tuning adjusts its values.

Pit mode

The VTX transmits at minimum power so as not to interfere with other pilots.

PNP

Plug-N-Play: built drone without a receiver.

Power loop

Full loop around an obstacle, climbing with throttle.

Props in / props out

Direction the props spin. Props out throws less dirt onto the camera.

Propwash

Shaking when the drone passes through its own turbulent air.

Rates

How fast the drone rotates depending on stick movement.

RC smoothing

Filter that smooths the steps between radio packets so feedforward and the motors don’t jump.

RHCP / LHCP

Circular polarisation of the antennas. It must match on the drone and the goggles.

RPM filter

Betaflight filter that removes motor noise based on their rpm.

RTF

Ready To Fly: complete kit with drone, radio and goggles.

S (4S, 6S)

Number of cells in series in the battery.

Saturation

When a motor reaches 100 % and the flight controller has no margin left to correct.

Setpoint

The rotation rate you ask for with the sticks. The PID tries to make the gyro follow it.

Smoke stopper

Current limiter for the first time you plug in a battery.

Split-S

Half a roll and half a loop downwards to change direction.

Stack

Flight controller and ESC on two stacked boards.

Step response

How the drone reacts to a sudden stick change. It’s the graph used to tune the PID.

Thrust linearisation

Setting that boosts motor output at low throttle so the PID has the same authority across the whole range.

TPA

Reduces the PID at high throttle to avoid oscillations.

Turtle mode

Spins the motors in reverse to flip an upside-down drone back over.

UART

Flight controller serial port for connecting a receiver, VTX or GPS.

VTX / VRX

Video transmitter on the drone / video receiver in the goggles.

Whoop

Micro drone with ducted props, ideal for flying at home.