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Backpack Info

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What is a Backpack?

A Backpack is an add-on device that facilitates wireless communication between an ExpressLRS module and another device (e.g. a Video Receiver on your goggles) using ESPnow as protocol.

Backpack Comms

Usage Scenario

You are setting up to fly with others and your favorite video channel is already in use. You're asked to use R2 as that's the vacant one. Using the ExpressLRS lua script, you change the setting into R2 (this while your aircraft is still unpowered). You power up your goggles equipped with a VRX Backpack. Then plug in your aircraft. Upon establishment of the connection, the VTX and the VRX are automatically set into R2. You're now ready to fly. No fiddling of channels on the OSD or on your goggles.

Okay, I'm sold. What do I need to get this working?

You already have the majority of the hardware needed. Most of the ESP-based ExpressLRS modules come with the TX Backpack. For the VRX Backpack, you can reuse any ESP-based ExpressLRS receiver (recommended are the EP1/EP2 receivers as they have boot pads, instead of boot buttons), or for a complete DIY route, you'll need an ESP-01F module.

An off-the-shelf VRX Backpack has also appeared from Happymodel: the EP82

See the tables below for the list of supported devices:

Supported TX-Backpack Targets

TX Module Support
Happy Model ES24TX ✔️ Fully supported
Happy Model Slim Pro ✔️ Fully supported
Happy Model Slim Ironman ✔️ Fully supported
Happy Model Slim T-Lite ✔️ Fully supported
Happy Model ES900TX ✔️ Fully supported
Happy Model ES915TX (STM32 version) ❌ Not compatible
FrSky R9 (all) ❌ Not compatible
Namimno Flash (STM32 version) ✔️ Fully supported
Namimno Flash OLED(ESP version) ✔️ Fully supported
Namimno Voyager (STM32 version) ✔️ Fully supported
Namimno Voyager OLED(ESP version) ✔️ Fully supported
Axis Flying THOR ✔️ Fully supported
HGLRC Hermes ❌ Not compatible
BETAFPV 2.4 TX ❌ Not compatible
BETAFPV 900 TX ❌ Not compatible
ImmersionRC Ghost TX ❌ Not compatible
QuadKopters 2.4 TX ❌ Not compatible
SIYI FM30 ❌ Not compatible
DIY TX ✔️ Fully supported with addition of a ESP8285

Supported VRx-Backpack Targets

Backpack Target Compatibility Tested?
Happy Model EP1/EP2 ✔️ Compatible Yes
Happy Model ES900RX ✔️ Compatible Yes
BETAFPV Nano 2.4 ✔️ Compatible No
Flywoo EL24E ✔️ Compatible No
Flywoo EL24P ✔️ Compatible No
Ghost ATTO ❌ Not compatible N/A
HappyModel PP ❌ Not compatible N/A
HGLRC 2400RX ✔️ Compatible No
JHEMCU / HiYOUNGER EP24S ✔️ Compatible No
JHEMCU / HiYOUNGER SP24S ✔️ Compatible No
JHEMCU / HiYOUNGER RX24T ❓ Unsure No
Matek R24-S ✔️ Compatible No
Matek R24-D ✔️ Compatible No
Namimno Flash (ESP) ✔️ Compatible No
QuadKopters Nano ✔️ Compatible No
SIYI FR Mini ❌ Not compatible N/A

Video Receivers currently supported include:

VRX Module Support
ImmersionRC Rapidfire ✔️ Fully supported (Versions 1.2.5 of the rapidFIRE firmware and later)
SkyZone SteadyView ✔️ Fully supported
TBS Fusion ❌ Not yet supported (check back soon)
Generic RX5808 Module ✔️ Fully supported
FENIX Module ✔️ Fully supported

I'm Ready to Proceed. What do I do next?

If your TX module is already equipped with a TX backpack (see list above), your next step is to update the firmware of the backpack. Proceed to the next page for more details.

If you're using a DIY TX module and want to add a backpack into it, proceed to the Backpack Wiki.

For the VRX Backpack, you will need to first update the firmware on the ESP device. The firmware will highly depend on which VRX module you will use it on. Proceed to this page for more info.

TX Backpack Setup VRx Backpack Setup

Backpack Usage

LED Status codes

  • Solid - Backpack is powered up and ready to receive packets.
  • Fast Continious Blinking - WiFi Mode is active and either the Access Point is ready for connection or the Backpack has connected to your Local WiFi Network (0.2.0; Home Network SSID and Password have been set).
  • Double Blink, Pause - Backpack is in Binding Mode. Using the ExpressLRS Lua Script, press Bind and the TX Backpack should bind with the VRx Backpack.

Button Operation (If present)

  • Pressing and Holding down the button during Power Up puts the device into Bootloader mode. From here, you can flash the firmware via UART using an FTDI dongle (USB to UART Bridge). LED on the Backpack device will be SOLID when in this mode.
  • Single Press during Normal or Binding mode will put the device into WiFi Mode.
  • Single Press during WiFi Mode will put back the device into Normal Mode.

Binding

Just like any ExpressLRS device, you can set a Binding Phrase for both the TX Backpack and VRx Backpack so they automatically bind with each other during power up. This Binding Phrase can be the same as what you used with your other ExpressLRS devices, or can be entirely different. The concept is the same.

Should you choose to bind manually, the procedure is as follows:

  1. Make sure you didn't flash the VRx firmware with a Binding Phrase.
  2. Power Cycle the VRx Backpack 3 times every ~30s. This interval gives ample time for your googles and VRx module to power up and down more gracefully. If your VRx Backpack has a button, it can also be used to power-cycle the device by cycling between WiFi Mode and Normal mode 3x (as WiFi mode reboots the device).
  3. The LED on the Backpack should now blink twice followed by a brief pause, then repeats, indicating it is in Binding Mode.
  4. Using the ExpressLRS Lua script, navigate into the Bind option. Press it once and the LED on both Backpacks should blink once and stay SOLID thereafter.
  5. Your Backpacks are now bound and connected and you can now use VTX Administrator on the ExpressLRS Lua script to sync your VTX and VRx modules.

Timeouts

When in Binding Mode (Double Blink & Pause) and no Bind packets have been received within 120s, the VRx Backpack will switch into WiFi Mode. This provides the users a means to enter WiFi Mode when their VRx Backpack doesn't have a Button.