Technical Support Transcript

RadioMaster RP2 ExpressLRS Firmware Flashing & Connection Troubleshooting

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User
radiomaster rp2 flashing firmware, should i use erase before flash?
Support AI

Yes, you should use the "Erase Before Flash" option when flashing your RadioMaster RP2 ELRS receiver.

While not strictly mandatory for every single minor update, enabling this setting ensures a clean installation by completely wiping any corrupted data or conflicting configuration files from the receiver's flash memory before writing the new ExpressLRS firmware.

Why You Should Erase Before Flashing

  • Prevents Bootloops: Residual data from older, incompatible firmware versions can cause the receiver to crash or enter a continuous bootloop.
  • Clears Bad Configurations: It resets all internal settings to factory defaults, eliminating unexplainable binding or telemetry issues.
  • Ensures Data Integrity: A full erase maps out the memory blocks cleanly, guaranteeing that the new firmware files compile and sit correctly on the chip.

Step-by-Step Flashing Recommendations

  1. Open ExpressLRS Configurator: Launch the official ExpressLRS Configurator software on your computer.
  2. Select Target Device: Choose RadioMaster 2.4 GHz as the device category and RadioMaster RP1/2 2.4GHz RX as the specific device.
  3. Choose Flashing Method: Select Wifi (recommended for the RP2) or Passthrough (via your flight controller).
  4. Enable Erase Setting: Check the box for Erase Before Flash in the flashing options section.
  5. Build and Flash: Input your binding phrase, click Build & Flash, and wait for the green success message.

What to Expect After Erasing

Because erasing wipes the memory completely, your previous binding phrase and custom settings will be lost. You must ensure that your correct binding phrase is entered into the ExpressLRS Configurator before flashing, or you will need to manually re-bind the receiver to your transmitter after the process completes.

User
when following the step from https://expresslrs.org, I get the following error: Build error An error has occured, see the above log for the exact error message... [truncated for spacing]
Support AI

A build error during RadioMaster RP2 firmware updates usually indicates local ExpressLRS Configurator issues, often resolved by clicking "Clear Cache" and "Reset PlatformIO" in the support tab. If the error persists, using the ExpressLRS Web Flasher to bypass the local compilation process provides a reliable alternative.

User
ok, I did that but still same error.. btw, does this look like a healthy discovery/connection for this process?: 
======== PASSTHROUGH INIT ========
Trying to initialize COM19 @ 420000
Attempting to detect FC UART configuration...
** Serial RX config detected: 'serial 2 64 115200 57600 0 115200'
Enabling serial passthrough...
CMD: 'serialpassthrough 2 420000'
======== PASSTHROUGH DONE ========
======== RESET TO BOOTLOADER ========
* Using full duplex (CRSF)
Cannot detect RX target, blindly flashing!
esptool.py v4.2.1
Serial port COM19
WARNING: Pre-connection option "no_reset" was selected.
Connection may fail if the chip is not in bootloader or flasher stub mode.
Connecting...
Support AI

No, this is not a healthy connection.

Your log shows that the software successfully initializes the Betaflight passthrough command (serialpassthrough 2 420000), but it completely fails to talk to your RadioMaster RP2 receiver right after.

The exact breakdown of why this log indicates a failed connection includes:

  • Cannot detect RX target, blindly flashing! – This means your flight controller is not receiving data back from the receiver. The Configurator cannot verify what chip it is talking to.
  • Connecting... – When esptool.py hangs on "Connecting...", it is screaming into a void. A healthy flash will immediately transition from "Connecting..." to displaying the chip type (e.g., ESP8285), MAC address, and flash progress bar.

How to Fix the Connection Error

The error happens because the receiver chip is either not powered up, not wired correctly, or failing to enter its internal bootloader mode. Work through these steps to fix it:

  • Power via LiPo Battery: Many flight controllers do not supply 5V power to the RX chip when plugged in only via a USB cable. Unplug the USB, plug in your drone's LiPo battery, and then plug in the USB cable to ensure the RP2 powers on.
  • Turn Off Telemetry: Open Betaflight Configurator, go to the Configuration tab, scroll down to the Other Features box, and turn off Telemetry. Save and reboot. Telemetry data flooding the UART line often blocks the passthrough tool from taking control.
  • Close Betaflight Configurator: Ensure the Betaflight Configurator app is completely closed before clicking flash in the ELRS Configurator. If Betaflight is holding COM19 open, ELRS cannot use it.