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…