As well as another standalone post, this is also part 3 of the comprehensive guide to building an FPV racing quad (check out part 1 here and part 2 here). Part 4 will be the build guide and will be posted in the next few days.
As with the rest of these posts so far, you may already know some of these parts so just scan through and read the parts that are most relevant to you. This is your quad, remember that. Do it the way you want to.
So, what exactly will we need for an FPV system?
Camera - The camera you will want to get will vary depending on the type of quad you build. For example, for some aerial photography (AP) platforms it is perfectly acceptable to use a GoPro as the FPV camera, but for racers there will be too much latency (lag) between the image and what is actually happening. As this guide is mainly for racing quads, we will look at issues surrounding these. The number one concern you will want to think about when choosing a camera for a racing quad is latency. Latency is the time delay between when the quad moves and when you see it move through the camera. Although latency in pretty much any system is much less than a second, for racers, that is still far too much. Racing quads move fast and you have to be able to react to changes as soon as they happen. In order to make latency as little a problem as possible, make sure you choose a CCD board camera with a resolution below 800TV lines (600-700 is better). You will want to choose a CCD camera and not a CMOS, as CCDs react better to changing light conditions and are less prone to distort the image when vibrating. Another factor to consider here is also the field of view (FOV) and it mainly comes down to personal preference. Most people's favourite field of view is the one they use, because they're used to it; so don't stress over this topic too much. The field of view, measured in degrees or implied by lens size (mm (less mm = wider FOV)), shouldn't be so wide that you struggle to realise where you're facing due to the distortion; FOV also shouldn't be so narrow that you have no idea of what is happening in the space around you (especially in proximity flying). To provide you with more info, I use a 2.1mm lens and thats about as wide (smallest lens size) you will want to be using, I may even get a narrower FOV camera in future. But like a good shirt, as long as you feel comfortable, you're using the right size.
CCD board cameras are not very expensive so you'll have a good range to choose from no matter what your budget is. My recommendation is to get something like a Sony security camera, they're very good, a good name and it's what I personally use and I think it's pretty good. You can get a camera on an open circuit board or one in a housing. In the housing it may be easier to mount (especially when you progress to tilting it (more on that in another post)) but it may also be substantially heavier and take up a lot more space, so bare this in mind. As long as it follows the guidelines above though, no matter what brand and type of camera it is, you'll probably be just fine with it.
Video Transmitter (VTx) - The VTx is an important component of the FPV system, sending the signal from the camera to the receiver so you can see the image. The VTx also dictates what frequency the signal is sent at and that is the main factor to consider when purchasing one of these. Most racing quadcopters use 5.8GHz VTxs and if you don't know much about this kind of thing then stick with that and you'll be fine. In general the lower the frequency, the better the penetration of the signal, but the larger the antenna has to be. 5.8GHz allows slight penetration, such as through light woods, fences, thin walls etc. and the antenna is a nice small size.
Another important consideration for VTxs is legality. The multirotor / drone community has bloomed at a very sensitive time in the world and the last thing we want, is to add fuel to the arguments for restricting their use because we broke laws on issues such as VTx transmission. In the US, you are legally allowed to use the 5.8GHz frequency as long as the power of the Tx is below 1W. Here in the UK (and I believe the rest of the EU also) the rules are much more restrictive; we can use the 5.8GHz frequency but only at 25mW or less power. So when choosing a VTx at 5.8GHz make sure you follow the respective rules. As a Brit, I can tell you 25mW works just fine so don't worry about the drop in power. Extra benefits of a low power transmitter are that it has less weight, it's normally smaller and it uses less power, obviously. If you choose to use another frequency, I suggest you look up the rules for that frequency in your area before proceeding.
When choosing a transmitter there's a couple of things you will want to make a note of, firstly the bands it can use (small differences in frequency that give rise to the different channels of that frequency) and whether the antenna connecter is SMA or RP-SMA. If you have a specific pair of video goggles or a receiver already in mind, make sure the Tx you choose can broadcast on the bands that your receiver will pick up. SMA vs RP-SMA is a completely useless argument as they are both identically as useful as each other, so just make a note of which one your VTx is but don't worry about choosing a VTx because of this. As for recommendations, you can't really go wrong as long as you choose something in the frequency and operating power that you've decided with the bands that you want to use. I personally use a generic non-branded 25mW transmitter with Bands A, B, C and Raceband from banggood and it works just fine.
Antennae - The main reason why the power output of the VTx doesn't matter that much is because of the antenna. As long as you are using a good set of antennae, you will not struggle to receive a clear picture from your aircraft. Most VTxs come with a linear dipole / whip antenna... Please don't use it. It's not that they're useless, they definitely do work. They're just terrible. You should get a pair of circularly polarised (CP) antennae in order to make sure your signal stays clear and works well. I won't go into the details of why because many people have done that elsewhere on the internet, all you need to know for now is that CP antennae work and they work well, so use them. When choosing your antennae make sure that the one you put on the VTx and the one on the VRx are polarised the same way, either right-handed or left-handed (RHCP or LHCP) or you're antennae will be almost as useful as the linear dipole ones already mentioned. Also antennae are built with a specific frequency in mind so make sure you get 5.8GHz antennae if your system will be using 5.8GHz etc. As long as you satisfy all these points, you won't really be able to go too badly wrong here but as a recommendation, I use Fat Shark/ImmersionRC SpiroNet LHCP 5.8GHz antennae and they work brilliantly. I will probably always use them. As the antenna is so important however, maybe stay away from the low build quality generic ones for this section.
Video goggles / screen / VRx - I've decided to combine VRx and the displays for a few reasons. Most video goggles either come with a receiver or have one built in and even if they don't (or if you choose to use a screen) receiver choice is essentially dictated by your choice of transmitter so it's not hard to choose one (Just make sure it's the same frequency and bands as the Tx).
The main decision to make here is goggles or screen? There are some obvious pros and cons to each. Goggles are not cheap, they are very far from cheap and while LCD screens also can be quite expensive they tend to be cheaper and more versatile than video goggles. Video goggles can mean better immersion in the experience which is both more fun and (some would say) focus you more on the flying. Goggles are also normally easier to set up and use and will come with their own power source. Goggles will also either come with a receiver built in or a module bay for taking one. The choice here is up to you but, in my personal opinion, goggles are better and they're all I have experience with, so we will focus on them now.
Goggles have a few different things to consider other than price (although that is another big factor). Firstly, FOV is again an issue with goggles. In this instance, the larger the field of view the better as it will help you get better immersion in the experience instead of squashing everything onto a small screen. Screen resolution is also another factor and like any screen, more is better. The aspect ratio of most FPV cameras will be 4:3, so a 4:3 screen (or a screen with enough resolution to compensate for the wrong aspect ratio) will work best. And lastly, the receiver itself. Some goggles will come with built in receivers so make sure they will have the channels and bands you want to use. Others will come with a receiver bay, so make sure that they also come with the right module, or that you get the right module separately. In terms of recommendations, there is already a clear leader in terms of market share in this section... FatShark. I personally use the FatShark Attitude V3s and I think they are brilliant in most ways. Like all products, they have some drawbacks (such as the fogging issue) but I will cover them in later posts, including how they are easily fixed. FatShark aren't the only manufacturers of good quality goggles though so make sure you do your research and choose a product that is right for you. You don't want to make such an expensive investment without knowing it's the right choice first.
So this concludes part 3 of the comprehensive guide to building an FPV racing quad.
Remember, like all the other posts in this series, this is a guide and not a rulebook. Build your machine how YOU want it, it's yours. But the more you know the better, so I hope this is a useful resource.
If you haven't already, make sure you check out parts 1 and 2 as well as checking back here in the next few days for part 4, the build guide.
Happy flying everyone!
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