FPV Lingo and Concepts

Learning The Lingo

There’s plenty to learn in this hobby, so just to make it a bit more interesting for the newbie, we try to create as many ambiguous terms as possible. We then throw them around in conversations and in YouTube commentary as if everyone knows what we’re talking about. So here’s a list of some of the more common ones.

Term: pin-out

Often heard: "Just check your pin-out, should be obvious enough"

Pin-out refers to the pin-out diagram which is supplied with most flight controllers these days. This will usually be a diagram printed on a sheet of paper and included with your flight controller. Alternatively there are online versions of the diagram as well. The diagram basically shows the flight controller with lines from each solder pad on the board to a selection of peripherals which can be soldered to those pads. Referring to this diagram makes wiring up your flight controller super easy. So when someone tells you “just check your pin-out” this is what they are referring to.

Term: Vbatt

Often heard: "You can just power it from Vbatt"

Vbatt refers to the actual battery voltage supplied by the battery. Solder anything to the positive and negative terminals on a flight controller where the battery plug wires are also soldered, is an example of powering something from Vbatt. Basically whatever you connect to these pads will receive the direct voltage from the battery.

Term: 5 Volt rail / 9 Volt rail

Often heard: "You can connect it to the 5 volt rail on the flight controller"

Often causing beginners to go searching for something that resembles an actual rail on the flight controller, this term describes more the purpose of the rail than its appearance. On a flight controller there will often be a number of pos neg pad sets. While ground is always common, the positive voltage on these will be a regulated 5 volts and will always provide 5 volts regardless of the changing battery voltage (aka regulated). Where the rail part comes in is that all these 5 volt pads are connected like being on a rail. Some flight controllers also have a 9 volt rail or a 10.5 volt rail. But in the case of 9 and 10.5 volts there is usually only one pad at this voltage so it’s not really like a rail – but anyway.

Term: UART (Tx Rx)

Often heard: "Look at the board - do you have any free UARTs?"

A UART (Universal Asynchronous Receiver Transmitter) is simply a communication protocol and actually not even specific to FPV drones. Many electronic devices will have UARTs for internal communication. It’s super simple – there’s 2 sets of pads and 2 wires. One wire carries signal in one direction and the other in the reverse direction – kind of like a conversation. In drones, UARTs are used to allow the flight controller to communicate with external receivers, video transmitters and GPS units etc. But for the beginner, the confusing part is this – nowhere on the flight controller board is the word UART written – just the words Tx2 and Rx2 for example or even sometimes T2 R2. These pairs of pads form a UART, and will sometimes be referred to on the pin-out diagram as a UART not Tx Rx. So just remember for example if you see T3 R3 next to pads on a flight controller, this means UART 3.

Term: All In One

All in One - Define "All" for me?

Once upon a time, we just had 4 In 1 and this referred to an ESC with all 4 ESCs on one board – well it still does. But then flight controllers were combined into one board with the ESCs and this is commonly referred to as AIO (All In One). But then we also have combo VTX / Rx boards caming out and terms like “All in One”, “3 In One” etc are widely used. But there’s no convention here. So when you read “All in One” it doesn’t necessarily mean “all”, it just means that multiple boards are combined.

Term: Cap

Often heard: "If you're running a 6S battery, you better use a cap"

Cap is short for capacitor. Often when building FPV drone we will solder a capacitor to either the battery plug connector or to the flight controller board right where the battery connector leads are soldered to it. The capacitor helps to stop battery voltage spikes which can damage your flight controller and other electronics by acting like a buffer of sorts to absorb these voltage spikes.

Term: LUA Script

Often heard: "You can download the LUA script from the company's website"

A LUA script is like a small program (an app) which can be run on your transmitter. LUA is actually programming language and used to create many types of programs – not just for FPV. But in the sphere of FPV, a LUA script downloaded and placed into a specific folder of your Open TX or Edge TX transmitter can expand its functionality. Companies which produce modules to plug into the module bay on the back of a transmitter will usually make available for download a LUA script which makes it easy to configure their module.

Term: High rates and low rates

Often heard: "Try changing your rates to get the perfect flight performance"

Rates are a setting in Betaflight which controlls how the drone moves in relation to your stick inputs. In particular, rates control how fast the drone will rotate and also how fast that rotation will be brought on at different stick positions. In general, low rates make the drone movement feel more gentle and high rates make it feel more snappy and crisp. With all the talk out there about rates – and people who really shouldn’t be giving advice, telling others to adjust their rates, beginners in this hobby can be excused for thinking that their quad isn’t going to fly properly unless they do something to their rates. Nothing could be further from the truth. Betaflight default rates are just fine for beginners. changing rates is not something that beginners should contemplate doing until they have reached a stage where they can actually fly with some degree of competency.

Term: Props in / props out

Often heard: "Motor direction depends on whether you are running props-in or props-out"

Props in or out describes the direction the props are rotating – see diagram for an example. Basically most bind and fly drones these days are running props-in. Some scratch builders may choose to run props out and prop direction can also be changed in betaflight. Proponents of props-out will tell you it is better for efficiency as well as not clogging up your stack with grass clippings when doing a flip after crash. They may be technically correct about the efficiency but I doubt half of them could actually tell the difference. For the beginner and just about everyone else, just go with the manufacturer’s default. I like to run props-in on all my quads just to have uniformity and so there are no mistakes when replacing props.

Term: 2204 (in reference to motors xx-xx)

Often heard: "The best motor for this quad is a 2204"

All motor sizes in FPV are stated by a combination of 2 sets of numbers. In this example 22 stands for 22mm which is the width of the stator (the part inside the motor which doesn’t move). The second set of numbers is the stator height. in this example 04mm (4mm). A good (but rough) calculation of motor strength is (Stator Diameter / 2)Squared * Pi * Stator Height which gives the stator volume (not taking into account the displacement of the bearing or shaft). Important to remember is that a narrow tall motor will be more powerful at high rpm and a wide flat motor will be more powerful at lower rpm.

Github and Open Source (overview)

The following terms relate to open-source software and the Github website which is used by many developers of FPV related software. The concept of open source and FPV have been intrinsically liked right from the very inception of this hobby. In fact, most major developments in this hobby have been firmly driven by members of the FPV community itself. As you venture into FPV you will surely be hearing much more about open source projects.

Term: The devs

Often heard: "I hear that the devs are working on that and will have an update soon"

The devs means the software developers. In the case of open-source software these are usually talented and skilled computer programmers who also have an interest in FPV and who dedicate their time for free usually as part of a team to develop the open-source software.

Term: Forking and Pull Requests

Often heard: "Another group of programmers has forked this software to develop that feature. They should submit a pull request soon."

So first of all, the whole concept of open source is that no one owns the software. Anyone can take that code base and expand on it or change it. The only condition is that their work on the software also remains open source. When another group of programmers takes the code base and starts working on it themselves to implement features they desire in the software, that’s called “Forking”. If they then feel that the changes they made should be implemented back into the original code base, they can submit a “Pull Request” to the original developers. If the original developers accept the pull request then that extended functionality will be implemented into the original “official” software.

Term: Repo

Often heard: "What do you mean you can't find it - just download it from the repo."

A repo or repository is an online shared storage space that anyone can download files from. Open-source development teams will have a repository on their Github site. Many FPV manufacturers will also have a repository, usually on their official website, from which firmware versions, user manuals or VTX tables can be downloaded.