ExpressLRS Explained: What Binds to What

ExpressLRS is the control link most FPV aircraft now fly on: open source, very long range for the money, and low enough latency that nobody argues about it. It also has a naming problem that costs beginners real money.

The two halves

Every radio link is two devices, and they are bought separately.

• The transmitter is the radio in your hands. One purchase, outlives many aircraft.
• The receiver is the small board in the aircraft, and you need one per aircraft.

Both must be ExpressLRS. This sounds obvious and is the single most expensive mistake people make, for a reason worth spelling out.

The trap: "ELRS" versus "4-in-1"

Most popular handsets are sold in two versions of the same model, at similar prices, under nearly the same name:

• the ExpressLRS version, with an ELRS radio built in
• the 4-in-1 multiprotocol version, with a multiprotocol module that speaks FrSky, Futaba, FlySky and others — but not ExpressLRS

A 4-in-1 handset will not bind to an ExpressLRS receiver out of the box. You can add an external ELRS module and it will work fine, but you have then paid twice.

When we stocked handsets we dropped one otherwise-attractive listing entirely because its own description claimed an internal ExpressLRS module in one line and listed the multiprotocol chipset in the next. Read the RF section, not the title.

Getting the two to talk

Three things have to line up:

1. Firmware versions must match. ELRS major versions are not cross-compatible — a v3 transmitter will not bind a v2 receiver. Both ends are flashed from the ExpressLRS Configurator, and doing both at the same time is the path of least pain.

2. The binding phrase must match. ELRS binds by a phrase you type into both ends rather than a button ritual. Use the same phrase on the handset and every receiver and they bind on power-up, permanently, with nothing to press. Use a phrase nobody else would pick — it is effectively the key to your aircraft.

3. The flight controller needs a spare UART. The receiver speaks CRSF, a serial protocol, and it wants a free serial port on the flight controller. Setup is in Betaflight, or ArduPilot on larger autopilot-driven aircraft.

Packet rate: the one setting worth understanding

ELRS lets you choose how often the link updates, typically from 50 Hz up to 500 Hz or 1000 Hz. The trade is simple and physical:

• High rate — lower latency, better for racing and hard freestyle, shorter range.
• Low rate — the receiver listens longer per packet, so it hears a weaker signal. More range, slightly more latency.

Racers run 500 Hz. Long-range pilots drop to 50 or 100 Hz and gain kilometres. There is no setting that is best at both, and anyone claiming otherwise is selling something.

2.4 GHz, 900 MHz, and Gemini

2.4 GHz is the default: small aerials, plenty of range, and the band nearly everything is on.

900 MHz penetrates obstacles better and carries further for the same power, at the cost of larger aerials. It is the long-range choice.

Gemini — also called Xrossband — transmits on both bands at once and receives both streams simultaneously. It is genuinely useful: something sitting on one band does not take your link with it.

The catch, and it is the same shape as the 4-in-1 trap: a Gemini receiver needs a Gemini transmitter. Put a dual-band receiver behind an ordinary 2.4 GHz handset and it works — as a 2.4 GHz receiver. You have bought a capability you cannot use.

What we stock

Receivers, in the aircraft:

Receiver	Band	Weight	Price
RadioMaster RP1	2.4 GHz	2.2 g with aerial	$27.59
RadioMaster DBR4	2.4 GHz + 900 MHz Gemini	—	$44.26

Handsets, in your hands — all four are the ExpressLRS versions:

Handset	Link	Price
Pocket	2.4 GHz	$94.79
Boxer (with case)	2.4 GHz	$215.99
GX12 Crush	Dual-band Gemini	$234.59
TX16S MK3	Dual-band Gemini	$275.99

The pairing that makes sense: RP1 behind a Pocket or Boxer, DBR4 behind a GX12 or TX16S. Mixing a DBR4 with a 2.4 GHz-only handset is money spent on nothing.

None of the four include batteries — they all take 18650 cells, and every listing says so, because a radio that will not switch on is a bad first evening.

Picking a handset

Pocket if you are starting, or want something that goes in a bag. Full ELRS, hall gimbals, and an expansion bay if you later want 900 MHz.

Boxer if you want full-size sticks. The gimbals are the reason to step up; longer sticks give finer control around centre.

GX12 or TX16S if you are flying long range and want Gemini. The TX16S adds a 5-inch touchscreen and the processing to drive it.

Frequently asked

Is ExpressLRS better than Crossfire? For most people, yes on price and latency. Crossfire remains excellent and has a long track record. ELRS is open source, which is why it moves fast — the project is on GitHub.

Can one handset fly several aircraft? Yes, and this is the point of the binding phrase. Put the same phrase on every receiver you own and they all bind to the same radio.

Do I need a licence? Not for these power levels in the US. Registration for the aircraft is a separate question — see the FAA's getting-started page.

My receiver blinks but will not bind. In order: mismatched firmware major versions, a mistyped binding phrase, or the wrong UART in Betaflight. It is almost always the first.

Is 2.4 GHz enough range? For freestyle and racing, comfortably. People fly tens of kilometres on 2.4 at low packet rates. 900 MHz is for going through things, not merely far.