Kyosho Mini-Z MR02 - 27MHz upgraded to FHSS!

I recently came across some information on the Mini-Z subReddit that has allowed me to make use of an old Kyosho MR02 model that I bought about a year ago but never had a 27MHz transmitter for.

So for anyone searching the internet that wants to get an analog 27MHz MR02 up to FHSS (regardless of whether or not the chassis is still "valid" or whatever...) here is what you need.

Kyosho MA-020 Receiver Set (RA45)

- The Kyosho MA-020 Reciever Set (RA45) - a soldering iron. 

The MA-020 board is the same width as the 27MHz MR02 board and it matches the retention pin size at the motor end.

The wires are mostly different length to the original board and some are not long enough so will need replacing. Here are my build notes.
 
- Extend the wires for the servo pot (reuse the old ones from the MR02 board)
- The servo motor wire is fine and about the right length.
- The other wires are all a touch too long and would be tidier shortened down, but you can just tuck them away around the board.
- The aerial cable on the MA-020 is a bit awkward for direct fitting, you may want to drill a hole for it in the chassis cover, but you can just tuck it in against the board with the other excess wires.
- The extra ports on the top of the MA-020 board for the gyro and USB setup do not fit under the standard 27MHz MR02 chassis cover. I decided I'd never use them on this model, so removed them. You could desolder them, or just chop them down with edge cutters, or if you're feeling crafty, get the dremel out and cut some suitable holes in the chassis cover. If you're handy with a 3D printer then maybe even print a new cover?

When you're putting it all back together also be sure to bind your radio before putting the lid back on, as the bind button is then hidden from access (unless you drill a hole for it).

I bound mine to my Radiomaster MT12 (with 4in1 module), and can now play with my old McLaren F1

 

Yokomo RS2.0 - Incredible budget 1/10 TC chassis

 
    The Yokomo RS 2.0 is a 1/10 scale racing car chassis, which is not only a Yokomo, it's also insanely cheap. In the UK, MB Models (Yokomo's UK distributor) has this priced at £150, and they throw in a set of pre-glued racing wheels & tyres.

    The RS 2.0 is a belt driven, 4WD, low centre of gravity chassis with racing specs and great levels of adjustability. It's highly driveable straight out of the box and comes with everything that people have been clamouring for in the low price space from the established brands. This is Yokomo taking the fight to the likes of 3Racing and Xpress in the entry level racing market. 

    To reach this price point Yokomo have opted to make the kit of plastic. But the plastics all feel great. We also have ball bearings throughout, plastic adjustable oil shocks, adjustable turnbuckles across all four corners of the suspension. There's space on the deck for full length and shorty packs, and for various internal arrangements. As you can see in the picture to the right, in my case I've put the ESC on the same side as my shorty LiPo in order to help balance out the left-right weight distribution. Even with my stubby servo and tiny radio receiver the motor still outweighs the battery and ESC. Maybe I'll try some bigger batteries?

    The kit all goes together perfectly as per the instructions, althought there is one omission from the instructions that I think is a necessary step. It misses out the lower belt tensioner piece from the instructions. It is an included part, with bearings, but just seems to go missing. The steps for building and installing it are in the RS1.0 manual though so you can check that out.

    Yokomo's "Rookie" cars are gaining traction and offer a great entry point to people looking to get into any class of racing. This RS2.0 is for the on-road touring car racers, then there the RO2.0 for your offroad buggy racing, and there's also the RD2.0 for the drifters. The kits all deliver well rounded adjustable cars, which you just need to add the electronics to.

    My RS2.0 has a Hobbywing Justock system in it, with the XR10 G3S ESC and Justock 21.5T G2.1 motor. This is the spec for the series I want to run it in. BRCA's latest on road series; the BRCA Sportscar Endurance Championship, based loosely on WEC LMH. It's an open chassis, with open tyre choices, but stock motor and blinky ESC. I've paired that with a SRT CH6012 low profile servo, which is a fast and plenty strong enough servo for lower speed 1/10 on-road racing. All I need now is a Montech LMH body shell and some RC friends to make up a team!...

    On my first test outing with the car, running basically kit setup (slightly higher, 6mm, ride height for my running spot) and no shell on it, I was amazed at how easy it is to drive. The 21.5T motor with stock gearing is actually a really good fit for the space I test my cars. I have some other cars (namely an upgraded Tamiya TA03RS and a Yokomo SO1.0) with lower turn motors and they can be a bit of a handful at speed here.

This is a quite excellent car that is priced immensely well. There's really not a lot more to say about it. The kit setup drives great out of the box and it's upgradeable to a decent level. It really is a superb car, let alone for the money!

I'll write an update when I have the shell and some track running under my belt!

UPDATE #1

    New shell for this car. I went with a hatch-back style frontie/rally shell because frankly I don't really like the modern TC shells (they don't look like actual touring cars). This is the Mon-Tech WR4, and my second paint job this year. I really quite like the shell. It's got a lot of nice details and it comes with some pretty decent decals to finish the look off. If you look too closely you'll see there are some paint bleeds on some edges (thanks to some old masking tape) but overall I like the colour combo and layout. Some of the worst offences are covered by the stickers and decals so got away with a few of them!

     I also now have a bit of track running time under my belt after a little trip to West London Racing Centre. The track over there is really nicely maintained and has a great surface. The grip levels are vastly higher than my home running/bashing spots and I was pleasantly surprised that the car could nearly flat out round the whole track bar a couple of the tighter corners. This leads me to thinking I'm definitely going to have to gear this car up a bit more as the stock gearing doesn't suit the 21.5T motor I currently have installed.

AGFRC A81BHPW 23kg Waterproof Servo

I got lucky and picked one of these up on eBay for under £40 and super impressed with this one. Probably the fastest servo I’ve come across. It’s also practically silent in operation.

It’s a Chinese made servo, built to a very high standard. AGFRC are actually an OEM maker for a number of other super high grade servo brands, so their own products are sort of a showcase of what they can build at a variety of price points.

It does however have some beautifully translated literature. My favourite line on the website page is probably this absolute gem:

    “Even in the wet and drizzle environment, can also satisfy your love of a model heart.”

Pure poetry I’m sure you’ll agree!

Anyway onto the important bit; how good is it?

This is a really very high quality servo. Strong, fast, quiet, and it re-centres really nicely. It's got plenty of torque, even at 6V, and is still very rapid. It goes al the way up to 8.4V and just gets increasingly powerful and fast! I’ve currently got it fitted in my Yokomo SO1.0 2WD racing buggy and, even with my poor mans ESC and motor, I can’t really think of anything that could make it significantly better for that application.
 

Here are the features and tech specs:
- Heat Sink Fast Cooling Design
- Fully Waterproof IP67
- Robust Steel Gears and Shafts
- Super Strong Three Ball Bearings
- Long Lifespan Brushless Motor
- Programmable Digital Circuit
- Lightning-Quick Speed
- High-Voltage Compatible
- High Precision Magnetic Angular Position Sensor

Stall Torque
12 kg-cm (167 oz-in) @ 4.8V
16 kg-cm (222 oz-in) @ 6.0V
19 kg-cm (264 oz-in) @ 7.4V
23 kg-cm (320 oz-in) @ 8.4V

Operating Speed
0.080sec/60° @ 4.8V
0.070sec/60° @ 6.0V
0.060sec/60° @ 7.4V
0.052sec/60° @ 8.4V

How to firmware update a RadioMaster MT12 surface radio

 

The Radiomaster MT12 is a complex beast. There are numerous parts to the controller that need their own, separately developed, firmware updates. It’s not the easiest process to follow from a completely new user perspective as it effectively has a few hardware parts that need firmware, and the EdgeTX operating system. All of which are regularly updated. There are guides on the various project websites, but they might not be the easiest to follow because they cover the update processes for all of the compatible radio manufacturers.

I'm going to breakdown the elements of the radio version that I have and use (with the ELRS internal board and the 4-in1 external module).

Breakdown of elements:

- EdgeTX operating system
- ELRS firmware (internal module)
- ELRS backpack firmware (internal module)
- RM 4-in-1 module firmware (external module)

Edge TX is the operating system of the radio and effectively the base firmware that everything else runs on top of. It’s worth keeping this as up to date as the radio allows, as it will improve functionality and correct any previous bugs of the radio software.

First let’s see if you need to update. With the radio turned on, press SYS, then page left to page 7/7. Here you'll see the version information. This will tell you what version EdgeTX is on. In my case, in the image below, I'm on v2.10.5 and at time of writing no newer versions were available.

If it was a lower version then the update process is relatively straightforward. Go to https://buddy.edgetx.org/ and follow the instructions by selecting the MT12 from the drop down menu. You can then update directly through the USB port on the side of your radio (under the rubber cover) or through the bootloader on the SD card.

Note; On my first attempt to connect the browser through the USB port on Windows 11, the device didn't show up on the list. I had to fix the USB driver using the following link:  https://impulserc.blob.core.windows.net/utilities/ImpulseRC_Driver_Fixer.exe 

Once I'd done that the SMT32 Bootloader device  appeared as it should. I was then able to update with no problems at all. This updated both the bootloader version and the EdgeTX version.

ExpressLRS is the protocol that the internal module uses as the radio link with the vehicle receiver. It's an open source protocol that is regularly updated and is probably the most advanced radio control protocol on the market today.

To check the ELRS version press SYS and on the TOOLS page scroll down to the ExpressLRS entry (LUA script). In here are lots of configuration options for the transmitter and offers some receiver control too. Scroll right to the bottom (or scrolling up one take you there too) and you'll see the version number above the Exit option. I my case as shown in the picture below, I'm up to date on 3.5.3 and no newer versions were available at the time of writing.

If you have a lower version then it's worth updating to take advantage of new features, performance enhancements and any bug fixes since your version.

To update you'll need the ExpressLRS Configurator. This is available from: 

 https://github.com/ExpressLRS/ExpressLRS-Configurator/releases 

Download the latest version for your computer operating system, and install it. Once you've installed it, run the program and follow the instructions (quite similar to the EdgeTX process). Select your device from the drop downs (RadioMaster 2.4GHz and RadioMaster MT12 Internal).

You can go about ELRS updates in a couple of ways. I recommend to either go through the USB port (EdgeTX Passthrough) or to update via WiFi. USB is definitely faster though.

I won't go through the device options and settings here, you can probably leave them as they appear and be fine. I'll do a separate post about those later.

Once you've got your radio plugged into USB select USB Serial (VCP) and it should appear in the device COM selection as STMicroelectronics. You may have to manually select it from the drop down if it doesn't select it automatically.

Note: If it doesn't appear in the list (like it did for me on Windows 11), then go to this site: https://www.st.com/en/development-tools/stsw-stm32102.html to download the latest version. Once that's installed you should be able to select it and update your radio.

ExpressLRS Backpack is only really a feature used by other control devices to control the radio. So for example if you are using FPV goggles and want to make changes to the radio, you can see what you are doing inside the goggles. I'm not personally using this functionality, but I feel like it's probably worth having this feature up to date with your ELRS version in case you find yourself thinking about FPV. The update process is basically the same as the main ELRS update. Choose your version, then your radio, and flashing method. Then hit the Flash button and it should work. To check your installed version you'll see the "backpack" listing in the ExpressLRS settings; scroll down and you'll see the version.

RM 4-in-1 module is the module that clips onto the top of the radio and gives us multi protocol support through 4 discreet chipsets built in. There is an internal module also available in the 4-in-1 version of the MT12. This guide is for my version of the MT12 which has internal ELRS and an external 4-in-1 module.

First things first, again, we'll check the version number. With a model selected that has the external module active, press SYS and go to page 7/7 again and select Modules/RX version. In there you'll see the Ext module version. As seen in the picture to the right mine is V1.3.4.12 (which is the latest pre-release version at the time of writing).

The downloads of the latest firmware can be found here: https://downloads.multi-module.org/ 
Select your configuration from the left drop down box. In this case with the external module we will select RadioMaster RM 4in1 External Module.
Then select the options on the right to narrow down the downloads to the one you need. Once you've selected the module in the left box you'll just need to select Firmware type: Surface and Channel Order: AETR. This should bring you to the bottom of the page where the firmware version you need is listed. In this case it's called "mm-stm-serial-aetr-sfc-v1.3.4.0.bin".

To install you can connect over a couple of methods. For this I like the flash from radio method. But I'll touch on the Flash Multi app too. Basically add the .bin file you downloaded to the SD card Firmware folder by using the USB port under the flap (use the storage connection method). Once it's transferred just navigate to the SD card and Firmware folder (page 2). Hit select on the firmware file and flash to ext module, and that should start the update.

Note: The MT12 has a low character count screen. Files with too long names will be excluded from the listings, so rename the .bin file to something shorter like "4in1-fw-v1.3.4.0" so that it appears in the list. 

The other method is by using the Flash Multi app, which uses the USB port on the top of the module. Download your firmware, download the app (from here: https://github.com/benlye/flash-multi), run the app and add your firmware to the app. Select the right com port, like for the ELRS and EdgeTX update tools and hit the button. Should be quite quick.

For the very latest test builds of firmware for the 4in1 multi module go to:
https://downloads.multi-module.org/latest-test/

And there you go a fully updated controller!

 

I hope this helps a few people out as I know this is a complicated controller, but well worth perservering for the performance to price ratio! Keep an eye out for more guides to this controller.

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!