Brief Summary
This video provides a comprehensive overview of radio control protocols used in the hobby, focusing on how receivers communicate with other components in a model, such as servos, speed controllers, and flight controllers. It explains various protocols, including PWM, PPM, SBus, and CRSF, highlighting their advantages, disadvantages, and suitability for different applications. The video also touches on Telemetry and recommends CRSF and SBus as the go-to protocols for new builds.
- PWM is the most basic protocol, widely used in cars, boats, and planes without flight controllers, but requires individual wiring for each component.
- PPM improves upon PWM by sending signals one after another down a single wire, but is still an analogue signal and not particularly fast.
- SBus is a digital protocol that sends channel values in a packet, offering faster speeds, no need for calibration, and the ability to send extra information like error checking and fail-safe status.
- CRSF is a modern, fast, and robust protocol that supports both radio control and Telemetry, making it a preferred choice for newer systems like ExpressLRS.
The video introduces a discussion on radio control protocols, specifically focusing on how the receiver communicates with other components inside a model, such as servos, speed controllers, and flight controllers. The presenter aims to consolidate information on these protocols, addressing common questions from pilots, especially those new to flight controllers like INAV, Betaflight, and RUDPilot. The video serves as a companion to a previous one on ESC protocols, acknowledging the rapid innovation in this area over the past 8-10 years.
The presenter notes that radio control protocols are constantly evolving, with current standards potentially changing in the near future. The focus is primarily on digital protocols like SBus, CRSF, and MAVLink, which are designed for use with flight controllers and stabilisers. A key advantage of modern protocols is their two-way communication, allowing Telemetry data to be sent back to the radio, providing pilots with crucial information like speed, altitude, and battery status.
PWM is described as the foundational protocol, commonly used in the hobby. It involves three wires per output: ground, +5V, and a signal pin. The length of the pulse sent along the signal wire determines the signal size. A significant drawback is the need for precise measurement of these pulses by the receiver, servo, or speed controller, often requiring calibration. PWM is relatively slow, with standard speeds of 50Hz for analogue servos and up to 150Hz for digital servos, and it only supports one-way communication. Each component requires its own set of three pins, leading to a large number of connections for multiple servos and speed controllers. Despite its limitations, PWM remains widely used in cars, boats, and planes without flight controllers.
PPM is presented as an improvement over PWM, especially for systems with flight controllers. It sends signals one after the other down a single signal wire. While this reduces the number of wires, PPM is still an analogue signal, requiring accurate pulse measurements. The need to wait for all signals to be sent before the cycle repeats makes it a slower protocol.
SBus is highlighted as a significant innovation and a widely supported open standard for digital signals. It uses the same three wires as PPM (ground, 5V, and signal), but instead of sending pulses, it sends a digital packet containing all channel values. This allows for much faster communication, as the signal transmission time is consistent regardless of channel values. SBus eliminates the need for calibration, as discrete values are sent for each channel. Additionally, SBus packets can include extra information like error checking and fail-safe status, enhancing reliability and functionality.
The presenter briefly mentions other protocols like IBus, FPort, DSM, and DSM2, noting that these tend to be proprietary. While they may offer improvements over SBus, their limited support across different manufacturers can lead to compatibility issues. The presenter prefers sticking to open standards for broader compatibility and ease of use.
The discussion shifts to Telemetry protocols, which enable data transmission from the model back to the radio or PC. SmartPort, developed by FrSky, is a common method where the SBus connection is used for control signals, and Telemetry is sent back via a separate SmartPort pin. MAVLink, used in Pixhawk and U Pilot systems, employs a robust two-cable system (receive and transmit) for both radio control and data transmission, allowing live Telemetry display on a computer. CRSF, popularised by Team Black Sheep and adopted by ExpressLRS, uses four wires (ground, 5V, transmit, and receive) for fast and reliable two-way communication, making it a preferred choice for modern systems.
CRSF is further emphasised as a go-to standard, with the presenter expressing gratitude to Trappy for allowing ExpressLRS to adopt the protocol. Most modern flight controllers have specific ports for CRSF receivers. Connecting the four wires and configuring the flight controller for CRSF provides a robust system.
For new builds, the presenter recommends using CRSF with ExpressLRS, TBS Crossfire, or the Tracer system. This setup offers Telemetry, reliable radio control signals, and advanced features. SBus is also recommended as a widely supported open standard, particularly useful for flight stabilisers and older equipment. The presenter suggests using up spare SBus receivers but opting for ExpressLRS with CRSF for new setups.
The video concludes by summarising the benefits of CRSF, which allows both Telemetry and radio control through a single UART, compared to SBus, which requires separate connections for Telemetry. The presenter encourages viewers to ask questions and expresses hope that the information provided clarifies the complexities of radio control protocols.
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Transcript
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0:01 hello and welcome to the video today we're going to be talking about radio control protocols specifically the ones that the receiver talks to whatever else is inside the model will be that servos speed controllers flight controllers flight stabilizers or whatever it is that you have in there now I get lots of questions by pilots either coming into a new part of the hobby if they've been flying for a long time or coming into the hobby straight into the world of flight controllers inav beta flight rud pilot and there's a lot of information around the Forum some of it is quite old and because I get so many questions I thought it would be useful to put it all together and talk about what the protocols are talk a little bit about things like Telemetry 2 and give you my recommendations for if you're starting a build now where I go to now this is kind
0:47 of a companion to one that I did a little while ago that was talking about ESC protocols explained because that's a very similar thing there've been a huge amount of uh Innovation around these kind of things in the past 8 to 10 years so it means if you're looking in forums particularly if you're not looking at something that's very current it can become confusing because something that's three or four years ago might be raving about one thing where now if you look at an updated post raving about something else couple of caveats before we get into this radio control Protocols are changing all the time I'm recording this in June of 2023 who knows what the standards will be and the common choices in 2 or 3 years time so if you're watching it in 2 or 3 years time the information in here may be out of date
1:32 however two of the protocols that I'm going to talk about at the end which are my go-to choices I can't see changing anytime soon most of the newer flight control protocols that the receiver talks to other things inside a model that are not digital are designed really for things like flight controllers so things like sbus and crsf and mavlink and other things that we're going to talk about in a moment are really there for if you have a flight controller or stabilizer or something else that's expecting to talk to the receiver over a digital link and the great thing about some of the modern the latest stuff the protocols that are around is they are two-way not only can you send the positions of the controls on the radio to the something like a flight controller or stabilizer but crucially
2:18 the flight controller or stabilizer can send Telemetry back to your radio so you can have information displayed on your screen and that's incredibly powerful because it means if you accidentally lose sight of the model or something happens to the fpv feed if you're flying you can actually fly the model with that virtual cockpit and get things like speed altitude battery status current drawn all that kind of stuff so let's get into the slides and talk about the one that most people bump into when they start in the hobby flying things like fix wi so pwm is the granddaddy of all of this pulse width modulation now pulse width modulation let's call it pwm because it's fractionally easy to say is the one that most people will be familiar with if they've been in the
3:04 hobby historically it has three wires that go into each of the outputs so on a receiver like this you'll see that the all these pins are actually set into groups of three there's a ground pin plus five volt pin typically and a signal pin and into those pins will'll plug in things like servos or things like esc's or electronic speed controllers pwm is one of the standards and the way it works is it sends a pulse along the cable and the length of that pulse is the size of the signal so it's a little bit weird what you kind of have to do is if you listen to these three beeps what value do they represent well you have to be able to time them exactly so hopefully you've got a really
3:49 accurate stopwatch and a very accurate thumb and that's one of the issues with pwm is that the receiver end or the servo or the speed controller has to be able to very accurately measure this pulse that comes along the wire coming from your receiver and that's why it's common to have things like calibration or setting midpoints for servos and things like that in pwm land the other issue is is that it isn't particularly fast you know 50 htz is standard for analog servos maybe 100 150 htz update speeds is okay for digital servos it's not super quick and it's only one way and the big disadvantage of course is that everything you plug into the receiver has to have its own set of those three pins so if you want to have eight servos connected and two speed
4:37 controllers you've got to have a receiver that has a whopping 10 pwm outputs or because each of those need three pins just receiver has to have room for 30 pins on it so that you can connect everything up and this is still very widely used in things like cars boats and planes and stuff without a flight controller it's a great way to put the it systems together without lots and lots of complexity now when Flight controllers came along initially we were doing exactly the same so we were connecting the Aeron using three wire cable and then we were connecting the elevator using a three wire cable the throttle with a 3 wi cable and it just became really really quite messy you can see here on this very old quadcopter how
5:22 many cables we had to manage however this next thing came along called PPM pulse position modulation and pulse position modulation is a great way to send the signals one after the other down just one signal wire so it was a massive Improvement for those with things like flight controllers over the other systems that we had if you had a receiver that could output a PPM stream then you plug that into the receiver the other end of the cable you plugged into your flight controller until the flight controller it was PPM however it's still an analog signal there's lot of little pulses and the pulses travel one after the other starting with channel one and going through right to the end of the channel so Channel 1 2 3 4 5 Etc so you still
6:09 have the issues with potentially the pulses need to be measuring very accurately and you still have the issue that it's all analog so all the timing has to be perfect and unfortunately having to wait for all of the signals all of the values to be sent before you round robin and start again means that it's not a particularly fast protocol however the next Innovation was one of the big ones and that is sbus sbus is still one of the standards lots of people in the community still think it's a legacy protocol but it is the open standard for digital signals that pretty much everything supports with the exception as I'm recording this of Express lrs but that's hope that's going to support it very soon so why is sbus
6:55 so much better than PPM because you still need the same three wires in the ground 5 volts to power the receiver typically and one signal cable and it's still sending all of the values across however this time rather than it's sending pulses that have to be measured so that you can get an idea of what all the channel values are it's actually a digital packet that's going over the wire rather like a computer network so this time rather than you have to measure the pulse to figure out that the value is 1427 then why not just send as part of the sign and say Channel 2 is 1427 and that's kind of exactly what sbus does a couple of massive advantages to that first of all you can send that information an awful lot quicker because of course in the older way with PPM if
7:42 all the channels had a really high value you had to basically wait to send those long pulses and do all that stuff with sbus it kind of takes the same amount of information to send the signal no matter what the channel values are the other thing of course is now we don't have to calibrate because using a digital protocol that's kind of all taken care of because the discrete value is being sent for all the channels you can just read it off at the other end the other massive Advantage with esus is that not only can you send the channel values because it's basically a packet of information you can in also insert and send extra information too you can do things like error checking to make sure that the information that you've just heard is actually correct things that computers do all the time you can also
8:29 do cool things like you can have other flags set up basically bits at the end that can be turned on or off which can tell you whether not you're in fail safe one of the things that you had to do back in the pwm OR PPM land was if you lost control of the model maybe your radio disconnected the receiver for whatever reason you had to set a really wacky value for one of the channels and tell the flight controller if you hear this wacky value it means something bad has happened in sbus you don't need to to do that because as soon as the connection has a problem the fail safe bit is sent along with all the other information and that fail safe bit is read by the flight controller or stabilizer and then immediately that initiates whatever you set up the fail safe to do so hopefully you can see here
9:15 sbus is Miles Ahead in terms of usability of pwm and PPM if you have flight controllers and stabilizers or other things that talk sbus you can also get things like sbus uh servos and all kinds of stuff but most of the time I run into sbus it's connecting a receiver to something like a flight controller now there are lots of other ones that you will bump into um I don't tend to use any of these the reason is that they tend to be proprietary protocols so people will take the esus standard and try and improve it and inverted commas and make it a proprietary protocol uh having a proprietary protocol isn't fantastic because it then means that everyone else has to try and figure out how to work with those protocols personally I like to stick with the Open Standards because going down these roads can get you into a little bit of trouble
10:03 because they're not as widely supported so personally I don't use any of these by the side but they are available and they belong to specific manufacturers so I burst is Fly Sky fport is f Sky DSM and dsm2 are Spectrum protocols three or four years ago it was very common to have flight controllers with a little port on the side that you can plug a spectrum satellite receiver into uh these days it's less common and things like SD as a grounder system so you will bump into them occasionally and if you are using all of their kits then there's a chance they'll all work together but a broad The Wider hobby they're less used so investing in them means that potentially you're going to bump into problems so we've talked a little bit then about how you get the signals from
10:49 the receiver in the model into your servos or ESC or your flight controller or flight stabilizer what about then that other thing that I've mentioned which is the T R how do you get Telemetry back down to your radio or even a PC well there's lots of different options that you'll bump into for that let me talk about some of the most common ones one of the most common ones is something called smartport smartport is something that free Sky develops and is on that receiver that we were looking at before there's a smart Port Port uh on the end of the flight controller and this is a very common way that lots of us used to fly 5 six seven years ago that we would have the S buus side of it plugged into the flight controller and then we configure
11:35 Telemetry going back into the receiver via the smart Port pin there's also something called mavlink mavlink is something that has been developed over in the pixhawk and U pilot side of the hobby it's a very robust two cable system so typically this would be plugged into a uart again just like the smartport would so you would have two connection to your flight controller one for your sbus and then one for your smartport with MAV link you can also use it for radio control but the fact it has two wires A receive and transmit pin means that you can also send data to the flight controller over this Telemetry link too and that's where it gets really powerful you can use things like Telemetry radios and have the live
12:21 Telemetry displayed on your computer because as far as your computer is concerned the radio link just looks like a really really really long USB cable last one to talk about then which is one of the Darlings of the hobby is crsf not to be confused with Crossfire Crossfire is a radio system developed by team Black Sheep crsf is the protocol that the receiver talks to the flight controller with again this is four wires so you have a ground 5 volts and you have a transmit and receive pin and that's going to be plugged into a UR on your flight controller and it sends the radio control information you know the position of all your radio controls to the flight controller but it also receives all the Telemetry back and sends it down to the radio it's an
13:07 incredibly fast robust brilliant system that TBS developed that's used in their Crossfire also in their TBS Tracer radio system but also now has been adopted by Express lrs which is the new open standard that no one vendor owns which is why all of us Pilots really love it and means then that crsf using those four connections power ground transmit and receive you have all the connections that you need and it's again a digital signal so it's like sbus on steroids with smartport with lots of other goodies involved too so we talked there about another radio control protocol crsf so what is crsf well I think crsf
13:53 going forward is going to become one of the go-to standards for the hobby I need to give a big thank you for trappy for not getting all litigious with the express lrs project when they essentially copied the crsf protocol it is probably the default way that I would recommend that people set up stuff now most flight controllers will have specific uarts and ports now that you would plug in crsf uh receiver most pilots who are coming into the hobby now are being advised to go with an Express lrs receiver or if you're not using Express lrs if you're using something like TBS Crosswire then by connecting those four wires and turning Telemetry on configuring your flight controller for crsf you get a really robust system
14:39 so if you are looking to build something right now what should you go for well I think it's becoming pretty clear hopefully from the tone of the video so far I would recommend if you have the option to use something like a crsf protocol with something like Express lrs uh TBS Crossfire or something the Tracer system that's what I would would go for you get the Telemetry back down to your radio you get the radio control signals sent from the little receiver into the flight controller it is fast reliable and it has lots of really cool features like a dynamically built menu system I'm not going to get into now but it just means there's lots of stuff in there that kind of future proof it and it's the reason why the express lrs team picked it as the protocol that their receivers talked the other one then is
15:25 good old sbus sbus is still a very widely supported open standard it's very rare to find a piece of equipment these days that doesn't at least support esus and although for a long time the express lrs team have viewed esus as a legacy protocol there is so much stuff out there that only understands sbus and PPM with that one wire connection particularly things like flight stabilizers for airplanes that you know what it's crazy that that project took so long to support it so for me these are the two options these days if I'm building something if I have a spare receiver that talks sbus and maybe we'll have a smart Port connection on it for Telemetry I'll use that just to use it up but if it's a new thing I really would probably grab
16:12 something like an Express lrs receiver running crsf and use that instead so hopefully that's been useful for those of you that have been trying to figure this out explains a little bit of what these things are and how it all works the nice thing about crsf is that with those four wires you can both get the Telemetry and the radio control stuff just using one uart with using something like sbus and a separate Telemetry connection then you're essentially using two uarts tying up two Hardware ports for that all to work which is why I think going forward crsf is probably going to become the default way that most of us do it if you have any questions pop them down below but hopefully now that all makes a little more sense thank you for watching the video
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