ExpressLRS on a Whoop: Bind Phrase, Packet Rate, Failsafe — Then Fly

Short version: flash the same bind phrase into the radio and the whoop, set the radio to 250 Hz, make one EdgeTX model with an arm switch, and prove that failsafe kills the motors with the props off. That is the whole job. Everything else in an ELRS menu is for later.

This is the setup behind every log on this site: a RadioMaster TX16S with ELRS (the one I fly, affiliate link) talking to a BetaFPV Air65. The RadioMaster Pocket is the same firmware in a smaller box — everything below applies.

1. Bind phrase, not the bind button

ELRS binds by a shared secret, not by a pairing dance. Put a phrase into the radio's ELRS firmware and the same phrase into the whoop's receiver firmware, and they are bound forever — every new whoop you flash with that phrase just connects. Use the ExpressLRS Configurator (or the web flasher) and type the phrase in the Binding Phrase field before you flash either side. Pick something you will remember; it is not a password.

The bind button and the three-power-cycles trick still work. Treat them as the fallback for a BNF that shipped without your phrase, and flash the phrase in afterwards so you never do it again.

2. Packet rate: 250 Hz, and stop there

On the radio's ELRS Lua script set the rate to 250 Hz. It is the sweet spot for whoops: low latency, plenty of range for a gym, and it leaves the 2.4 GHz band quieter than 500 Hz or F1000 for the people flying next to you. Telemetry ratio at the default is fine. Higher rates buy nothing you can feel on a 25-gram aircraft and cost link margin in a concrete building.

Leave the TX power at the lowest setting that gives full link quality indoors — 25 mW is usually plenty. More power warms the radio and does nothing for a whoop ten metres away.

3. One EdgeTX model

Make a fresh model, not a copy of something that came with the radio. It needs exactly four things:

• Internal (or external) module set to CRSF — that is what ELRS speaks.
• Channels 1–4 as AETR: aileron, elevator, throttle, rudder. Betaflight assumes it.
• A two-position switch on AUX1 for arm. Nothing else on that switch, ever.
• Optionally a switch on AUX2 for flight mode and one for beeper. That is the whole list.

Name the model after the quad. When you have three whoops with different tunes, you will be glad you did.

4. Prove it with the props off

Props off. Plug in USB, open Betaflight Configurator, Receiver tab. Move the sticks: the bars should track instantly, throttle low at 1000, centre sticks near 1500, full deflection near 2000. If a channel is reversed, fix it in the radio's Outputs page, not in Betaflight.

Then the test that matters: switch the radio off with the quad powered. The receiver tab should drop to failsafe values within a second and Betaflight should show RXLOSS and refuse to arm. Switch the radio on, confirm it re-links, arm on the bench with props off, listen for the motors, disarm. Only now do props go on.

5. Before you fly it, fly it in the sim

The same radio plugs into the browser sim as a USB joystick (EdgeTX: hold the radio's USB mode on connect, pick USB Joystick). Same sticks, same arm switch, same rates from the tune database. Ten minutes here beats a broken prop on the first real pack.

When it does not link

• Radio shows no link at all — the phrases do not match. Reflash one side; you typed it differently.
• Links, then drops in and out — receiver firmware is older than the radio's. Update the receiver to match the radio's ELRS version.
• Betaflight sees nothing on the Receiver tab — the serial port for the receiver is not set to Serial RX, or the provider is not CRSF. Ports tab first, then Receiver tab.
• Everything links but it will not arm — look at the arming-disabled flags at the bottom of the Setup tab. It is almost always the arm switch range or a level sensor calibration.