Radiomaster MT12 Setup - Edge TX and ELRS

In this article I’m going to collate as many general tips and insights for setting up the ELRS version of the MT12 that will help with link stability, performance and general usability. Hopefully a few of these can provide some insight into setting up your radio to highest level possible.

I’ll keep it as up to date as possible when I read and try new tips.

Receiver Numbers and Binding Phrases

    It's a really good idea to use receiver numbers if you have multiple models/receivers, and setting binding phrase if you are going to be running your models anywhere with other ELRS users. 

    These two settings sort of provide the base level "security" to the protocol. Only transmitters and receivers with the same binding phrase can bind to each other, and then will only control the set RX number set in the model binding menu. So a family could all have the same binding phrase, so they can share models, and then set the receiver number so they can each control different vehicles.

    At the track you'll want to set your binding phrase so that no one else can accidentally control your RC vehicles.

    Best practice for setting a binding phrase would be to simply pick two words and use that. The likeliness of someone else picking the same two words is very low. Treat it like a password so no one could guess it if they know you.

Arming

    I keep banging on about it, but Arm your control link. Putting the receiver into an Armed state is inherently important to the ELRS protocol (it says so in the documentation). It also fully enables the dynamic power mode. This is less important if you are using a set single power level, but is still a good thing to do in practice. 

    Arming is done through channel 5 (Aux1) on the protocol, which means, as a side note, that output channel 5 on the receiver should be swapped to a different input channel for useful control options.

Correct packet rate usage

    The packet rate is set in the ELRS LUA script and there are a number of choices you can make here, based on your usage case.

    In general, the guidance says, lower packet rates (lowest is 50Hz) means better range and greater link stability, at the expense of control latency and accuracy. 

Higher rates (highest is F1000) means faster control latency at the expense of maximum range and link stability.

    The D and F packet rate modes are FLRC modes. These provide higher data rates and lower latency, which ought to be best suited to racing applications.

The modes 50Hz-500Hz (including the ones with “full” designation) are LoRa modes. These employ chirp spread spectrum derived techniques for increased range and link stability. In the air, with even small ceramic internal antennas, LoRa can achieve flight ranges of up to 30km, and with larger antennas there are demonstrations of control over 100km! (In fixed wing models, and of course perfect conditions)

    I’ve chosen to use the 500Hz mode for my surface vehicles, which is the fastest of the LoRa protocol modes. A high link stability with long range and still very fast response time. I would certainly try it out at F1000 if I was doing a lot of racing, and found myself needing to get even less latency out of the system.

Receiver PWM output rates

    The receivers themselves can also be set to make the most of your servos and ESCs. It’s worth setting both to output at 330Hz to get the best response time to the control input. This can be done either with a connected receiver through the ELRS LUA script on the transmitter or via the WiFi connection on the receiver from a computer or mobile device.

Know your protocol

    The ELRS protocol has some specific functionality on channels 5 and beyond that are simply built in to the protocol. Most of this relates to the precision available on the latter channels, which are often limited to switch use rather than full analogue input.

    There is also the differences between the LoRa and FLRC modes of operation. Which are defined generally by extended range from LoRa and extended lower latency of FLRC. I covered them briefly when talking about the packet rate settings.

EdgeTX isn’t like other surface GUI operating systems

    It’s massively configurable but it’s also complicated to use. It’s what I’d describe as a low level operating system. In computer terms it’s closer to something like DOS than it is to Windows or Mac OS; more engineering focussed than your typical end user focussed radio. I can see a world where there is a build of Edge TX that has a more user centric UI which is pre-configured for easy access to the controls that typical surface users might want to get to quickly.

To be continued…

Radiomaster MT12 - Review

Hello again, today I am going to talk about my relatively new Radiomaster MT12 ELRS. I also picked up the external 4-in-1 module. I bought this with my own money and have no affiliation with any companies. This thing is packed with functionality, and probably one of the most complex radios ever sold to consumers… there is a lot to talk about!

 

The MT12 is a modular, open-source, 16 channel (32 with the 4-in-1 module) ground radio that at its core runs on the EdgeTX open source radio OS and uses the ELRS protocol. It also has an add-on module slot for running other protocols. In this case the “4-in-1” module that can operate a huge range of 3rd party recievers, including many RTR receivers like those from Spektrum, Futaba, Traxxas, Kyosho, Losi, FlySky and more.

Let’s start with the hardware.

This controller is quite chunky feeling and a nice weight in the hand. It’s a little bigger than your base level wheel controller, but overall feels much nicer throughout the controls. It has a really similar side profile to a Futaba model I was looking at the other day too (the T4PM). The wheel and trigger are both Hall Effect sensors which means there are no pots to wear out and next to no contact components, meaning incredibly smooth feel and operation. The whole thing feels quite premium compared to my intro-back-to-the-hobby radio, the Absima CR4S V2.

All of the switches and buttons feel pretty good too.

On switching it on we’re greeted with “welcome to EdgeTX” from the speaker. Nice but I’ll be switching that off. It also has some nice RGB LED’s (that are customisable) around the base of the radio and the grip. The screen is a monochrome LCD (my reference for these types of screen is “like a GameBoy”) with ok resolution and excellent readability; perfect for direct sunlight, and backlit for darker environments.

Scrolling the extensive menus is easy enough, though there are definitely some complex settings in there that I’ll need to dig into a bit later! 

Protocol: What is ELRS? 

The acronym stands for: Express Long Range System.

It is a long range and high data rate control protocol capable of 1kHz refresh rate and receivers driving servos up to 400Hz. It also runs telemetry back to the transmitter.

The top transmission range on ELRS is not measured in 100’s of meters but often quoted in kilometers or miles. It has astounding range in all modes.

The protocol was originally designed with air control in mind so range was key, but obviously adapting to ground usage means that maximum range is reduced, due to the physics of radio transmission, but still the range remains impressive on the across the floor even with obstacles in the way. 

The key here for me is the combination of never having to worry about range and that transmission speed, meaning I can take full advantage of the best servos while being nearly a kilometer away from my car!

This truly is where the magic lies in this Radiomaster system. Imagine a system with better range and similar control frequency at a small fraction of the cost of the best Sanwa or Futaba systems.

What does the 4-in-1 multi module do then?

Ok this is another fun trick this controller can do. The 4-in-1 module slots onto the expansion slot on the top of the controller. It has several chipsets inside that allow it to effectively emulate the protocols of numerous other manufacturers. This includes; Kyosho FHSS, FlySky AFDHS (various versions but not ANT), Radiolink, Dumbo RC, as well as some Traxxas and Spektrum receivers. 

The list is long but not everything is covered. Like I already mentioned, my old Absima CR4S V2 receivers don’t work as they use FlySky’s AFDHS ANT protocol, which is a different hardware chip than other AFDHS protocols. That’s a shame but not the end of the world. I’m looking forward to getting some RTR cars bound up to it in the near future.

How does it feel?

The build quality is about an 7 or 8 out of 10. The plastics feel good and the controls feel nice, but one of the buttons has a sharper edge than I’d like. The steering and trigger feel really nice and smooth with a premium resistance feel that I like quite a lot. The wheel runs smoothly and freely with a little centre bounce if you release the wheel fully sprung. That bounce is also reflected in fast servos capable of responding that quickly, which would suggest that the ELRS receivers are very capable for their cost and minimal size. 

Receivers 

The Radiomaster MT 12 ELRS transmitter comes with the ER3Ci receiver. A 3 channel receiver with a voltage telemetry input, that retails for less than £15. The other car specific (indicated by the C in the name) receivers are the ER5Ci and the ER5C V2. Both of which are 5 channel receivers with battery telemetry. The ER5C V2 has a wire antenna, while the other two "i" versions have a discreet internal ceramic antenna. Both are under £20.

There are several other receivers too without the C denomination that have other specific use cases like more channels and ports for additional telemetry data.

Customisation

Where to begin. This is probably the most programmable radio system available in the surface control space. EdgeTX allows a huge range of control variety, with control to channel mapping, mixes, curves, end points, trims, sub-trims, rates, centre point calibration and everything you could really imagine. It can even run scripts allowing you to program a single button to perform a series of commands.

You can even customise the hardware, with several modules that can clip into the base of the controller. The two included are a couple of switches, and game controller style joystick. Both of which can be custom programmed to perform additional tasks. The joystick could be handy in USB mode to get round menus and the like, which is how I have mine setup right now. But I can definitely see the benefit of the extra two switches for certain kinds of cars.

There is also the top module slot, which allows use of numerous radio nano-modules. These can be used to add additional radio protocols and functionality to the transmitter. There are a fair few on the market offering various flavours of ELRS, or the 4-in-1 module offering many protocols.

All of this advanced functionality does come with the downside of added complexity. It’s worth remembering that this operating system has been developed initially for drones so some of the translation of terms might not make full sense to some more experienced surface control users.

Other nice details

The controller comes in a nice fitted semi-hard case with all of the accessories and stickers in the back compartment. 

It runs on, and can charge, LiPo or 18650 LiIon cells (the radio includes a 18650 battery sled). Batteries are sold separately though so you’ll need to order some if you don’t have any around.

It’s a USB controller too. You can map this controller in most games that allow rebinding the controls. It’s plug and play on Windows. It’s not bad too. It’s fun to play racing games with a method that you know or want to practice with your wheel controller. So far I’ve found it a bit challenging compared to my Xbox controller but new control methods always come with a learning curve.

As an aside there are probably only a few games that are customisable enough to accept the controls. Here’s a couple I’ve found that work perfectly after binding the controls in the menu:

Wreckfest (modern day Destruction Derby)

VRC Pro (an RC racing simulator!)

Concluding thoughts:

In raw protocol performance terms this radio, in ELRS, is probably as close as you’re going to get to the top spec Sanwa, Futaba or Spektrum kit without spending £700. It’s important to quantify that by saying Sanwa and Futaba go out of their way to design incredible bits of kit, with the sole purpose of being racer centric, with all the key features laid out perfectly and simply for the top level racer, and as such are incredible transmitters with, probably, unrivalled reliability and performance. The MT12 and EdgeTX is maybe not quite everything they have, but it provides exceptional performance beyond any other product in it's price category, and can be customised and set up so that it does pretty much anything well, even if it takes a few more complicated steps to get there.

Despite really good documentation of both Edge TX, Express LRS, and 4-in-1 modules, there are still a few basic things that need explanation. I feel like a lot of the documentation is written from the aspect of existing users updating, rather than new product for new users. Many of the key points are being covered by an enthusiastic user base on YouTube. I will be putting together a couple of tutorials myself over the next few months for things that weren't exactly straightforward for the first time user. 

Some of the RadioMaster users of prior products are suggesting that there may well be a premium version of the MT12 on the way, if sales figures live up to expectations. This would probably bring along a high resolution colour screen and improved premium build quality, plus maybe a few extra control sources. But that’s all speculation really. If it does eventually appear then I’d likely get one as having a couple of EdgeTX ELRS controllers would be handy for racing freinds and family!

Radiomaster MT12 - ELRS Arming (Channel 5 / AUX1)

As these radios now come fairly well setup for basic use of throttle and steering out of the box, I’m going to start with something less obvious but massively important to new users and something which is not setup out of the box.

“Arming is an extremely important part of the performance of the control link.”

Arming the ELRS system. 

ELRS is not like most surface radio protocols, and EdgeTX is a very low level operating system that requires a bit of patience to get right. It's also capable of hosting several different protocols which need different attention. There are a few things specific to how ELRS operates that are important in the setup.

One thing that appears a lot in the ELRS guide is that arming on channel 5 (also named Aux1 on some radios and documentation) is really important to the performance and reliability of the radio link.

Why is Arming important? Well there’s a rundown from the ELRS website of what arming does and how it affects the radio link at the bottom of this page in the FAQ section:
https://www.expresslrs.org/software/switch-config/

It states that it basically improves performance and link stability. One key performance factor is that it fully enables the dynamic power mode, which I and others had been having trouble with (causing cars to runaway). 

Here are some key points:

"When IsArmed is enabled, these safeguards are applied:

- All "Button" inputs are disabled
- All "Joystick" (5-way buttons) are disabled
- Bump to Share is disabled
- VTX Admin is disabled
- Integrated VTX channel change is disabled

When IsArmed is enabled, these performance features are activated:

- Dynamic Power is fully enabled
- Race telemetry mode turns telemetry off
- Some thermal-based fan controls are enabled

Arming is an extremely important part of the performance of the control link. Please use Aux 1 / Chan 5 as indicated. Also keep in mind that for ExpressLRS, ~1000us is the disarmed state and ~2000us is the armed state."

That seems like evidence enough that this is important. So it needs to be set up as a priority to get the best out of the radio. But I’m going to start on a slight tangent…

In this Joshua Bardwell video he explains how to set a throttle override using a logical switch that is controlled by the physical switch SD on the base of the radio, next to the USB-C charging port. That function does two things on his setup: 

1. It overrides the throttle so it doesn’t respond while you’re handling the radio.

2. It indicates the state of the throttle by changing the LED on the base of the radio to either; red (off) or green (on).

The video should be set to start at exactly the right point where he starts the explanation:

Once that function is setup, I then wanted to add a third thing that I want this switch to do at the same time. That is to also send the ARM signal, from the transmitter, on channel 5. The arm signal is a simple 1 bit on or off. Set at 1000 is off and set at 2000 is on. Simple right?

Using L01 (as set up in the Bardwell video) as the source for mix 5 and output 5 I have set the output trims and min/max so that the correct, high/low signal is sent for arm states with the press of the button. Here’s a screenshot of how I have the channel 5 output set. You could probably also set the same output numbers with a curve.

So now when I enable my trigger/throttle input I also set my arm status to on, and the LED's on the base of the controller go green.

You can check the arm status by going to the ExpressLRS LUA script in the SYS menu. In there it will flash armed in the top left if it is armed and nothing if it’s not armed. You’ll also see here whether you have dynamic power set up or not. 

Early testing with my cars, running the Radiomaster ER3Ci and ER5Ci receivers, has shown this to be a reliable way of making dynamic power work as intended, without random runaways or failsafes going wrong! I’ll keep testing and running, and I’ll update if I ever get another runaway car!