The market for radio links has flipped on its head. FrSky’s ecosystem has become more closed and confusing and new offerings like Ghost and Tracer have expanded user choice. ExpressLRS is one of the most interesting developments: a high performance radio link that’s also open source. It’s an impressive project that’s grown from needing to DIY hardware or void your warranty to manufacturers making ELRS modules available off the shelf. Today, we’re looking at BetaFPV’s ELRS offerings, specifically the Micro TX module and ELRS Nano Receiver.
The ExpressLRS project makes a lot of promises:
- Runs on a variety of hardware
- 900MHz or 2.4GHz hardware options
- LoRa modulation
- Selectable packet rates from 25hz (long range stability) to 500hz (low latency control)
- Superior range and stability to other current-generation radio links
This is an extensive set of claims, and promises to become a competitive offering in the radio link market.
The first recommended step is a firmware upgrade. ExpressLRS provides a nicely designed configurator program to be able to flash transmitter and receiver alike. This is helpful for a few reasons. First, it ensures all of your hardware is on the same firmware version. Second, it allows you to set up a “binding phrase”.
The binding phrase eliminates the commonly annoying bind process because all transmitters and receivers flashed with the same phrase are automatically bound. The “binding phrase” is explicitly stated to not be a secret, and pilots are encouraged to share theirs with others so there’s no overlap. This system does rely on trust of other users. If a user copies a bind phrase, it’s possible to have collisions when creating radio links. The ELRS link may therefore not be suitable for commercial applications. (There’s a process for binding without the phrase, but it’s really no simpler than other systems.)
The ExpressLRS Configurator is easy to use and provides lots of options. Depending on the hardware, you can flash a transmitter via USB or WiFi. For receivers, both of those options are available, plus BetaFlight passthrough—having the receiver normally wired for flight and connecting to the flight controller’s USB. Some options like WiFi depend on hardware support. Updating over WiFi is surprisingly easy. Once you have the firmware file you wish to upload, simply connect to the hotspot and select it from your local system.
Since firmware is customized with your phrase and options, you need to build the binary file from source rather than just downloading it. This isn’t a complicated process—the configurator takes care of all the details for you. However, it does take quite a bit of time when you first start using the tools. The initial build process requires downloading the entire compilation toolchain. The good news is once it’s installed, subsequent builds and updates go much faster.
BetaFPV’s ELRS System
Looking at BetaFPV’s equipment specifically. BetaFPV currently offers two transmitters to fit different sizes of module bay: the ELRS Micro TX Module for radios like the Frsky Taranis X9D and TBS Mambo, and the ELRS Nano TX Module for radios like the FrSky Taranis X-Lite, FrSky Taranis X9D Lite, and TBS Tango 2. On the receiver side, there’s an ELRs Nano Receiver which we’re looking at here, and an ELRS Lite Receiver which is extremely small but has lower power output. They also offer a full transmitter with the LiteRadio 2 SE, (or as a main board upgrade for it), some Flight controllers with the ELRS receiver built in, and several RTF drones with ELRS.
ELRS Micro transmitter
The “Micro” module fits a full size JR module bay and brings the following feature set:
- Supports the full range of frequencies and packet rates of ELRS
- Up to 500mW output power
- Onboard 100mW power amplifier for telemetry
- 5–12V input voltage
- 5–12V (2S) XT-30 external supplemental power connector
- USB-C data port
- RGB LED
In the box is the module itself, a typical dipole antenna, a moxon antenna (sized appropriately for your frequency), USB-A to USB-C cable (not shown), and a user manual. You have to purchase the module with the frequency range you’re interested in using. We’re looking at the 2.4GHz version. There are two 900MHz variants: 915MHz and 868MHz, which are used in different parts of the world. Test units like the one we reviewed did not include the USB-C cable; but the USB port is small and not all cables fit well. BetaFPV now ships a cable so everyone has one that fits.
The transmitter sports an OLED and control stick for changing settings, but these features don’t seem to be fully fleshed out. The directional arrows on the stick don’t do anything at all; it’s as if it only has a one-button interface. You change settings and make selections with short or long presses of the center button. The RGB LED has a range of user-settable colors to personalize your module, but can’t be shut off. Annoyingly, the color setting isn’t saved to memory and goes back to Cyan after a power cycle. Finally, the LED, control stick, and screen only work if you’re using BetaFPV’s fork of the ELRS software, which has to be specially loaded. Flashing an official version disables all three (that’s one way the shut the LED off). BetaFPV states this will be part of the official project soon.
The Nano receiver is a great fit for most full-size applications such as long range setups or when size is not the most important consideration.
- 0.7g, 12mm×19mm
- Input voltage: 5V
- Supports 500hz refresh rate
- 100mW Telemetry output
- Antenna connector: IPEX MHF/u.fl
- Output protocol: CRSF
In the box you get the receiver, a “T” antenna, connecting wires, a 4-pin header, 2 pieces of heat shrink, and a user manual.
The receiver is small, but not exceptionally so—it’s a little larger than an R-XSR or Crossfire Nano RX. Still, this package includes hardware WiFi and an amplifier for 100mW telemetry output. You can wire it straight to 5V and a pair of Tx/Rx pads on just about any FC; no fancy inversion is needed. Install and mounting is about the same as any other receiver. I ran into an issue where the included heat shrink depresses the onboard button once shrunk down. This makes it impossible to update firmware, so I had to cut the shrink back to release it.
BetaFPV also offers a Lite receiver which is just 0.5g and 10×10mm, with an included onboard antenna. You’ll have reduced range with the antenna and less power for telemetry, but it looks like a great option for micro builds or when weight savings is more important than range.
The system has an impressive record distance list on its github page, with claims of flights up to 40km without failsafes on just 10mW output power. Our test only covered typical close range flying, but we didn’t experience any link issues at all, in each case outflying our video signal. That’s more than enough for most people. A professional pilot may be able to tell the difference between a 500Hz data rate and something much slower, but most casual users aren’t going to notice. The flight characteristics of the aircraft—power, size, weight, prop pitch—make a much bigger difference in responsiveness. Unless you’re already pushing the edge of performance on your aircraft, upgrading the link may not provide much advantage in how much control you have.
If you research the BetaFPV gear in particular, you may find some speculation about hardware setup and heat dissipation issues that were largely related to the development units. BetaFPV has responded to this in fair detail on Facebook. It’s a nice bit of transparency to see from any manufacturer.
Of all the changes in control links that have appeared recently, ExpressLRS is one of the most interesting for us here at Propwashed. The link quality and capability is impressive, manufacturers seem to be getting behind it, and it’s no secret that we like open source. In addition, it’s enabled an even lower price point than we’re used to for radio links, with transmitters and receivers at half the price or less than competing systems. In addition, the ExpressLRS team is knocking it out of the park on usability features like WiFi updates and system documentation—The Info section of the site is easier to read and understand than most system manuals. We’re really happy to see this development and the weight behind it from manufacturers such as BetaFPV.
BetaFPV’s ELRS line
- ELRS Micro TX Module
- ELRS Nano TX Module
- Moxon Transmitter Antenna
- LiteRadio 2 SE (or main board upgrade)
- ELRS Meteor65 Brushless Whoop
- ELRS Meteor75 Brushless Whoop
- ELRS Meteor85 Brushless Whoop
- ELRS HX115 LR Toothpick Drone