Technical Architecture

Technical Architecture

ELRS Mobile is not just a web-wrapper; it is a native Dart implementation of the ExpressLRS compilation and configuration pipeline.

Unified Firmware Assembly

Instead of relying on a remote cloud compiler, the app dynamically builds binaries locally on your device. When flashing ESP32/ESP8285 targets, the FirmwareAssembler:

1. Extracts the base generic firmware from the cached firmware.zip.
2. Trims the base padding by seeking the ESP 0xE9 magic byte.
3. Extracts your specific target’s pinout and configuration from hardware.json.
4. Byte-packs the 128-byte Product Name, 16-byte Lua Name, 512-byte user options.json, and 2048-byte hardware.json directly into the end of the binary stream.
5. Compresses the final payload into a .gz file dynamically if the target platform (like esp8285) strictly requires it.

Regulatory Domain Logic

The app accurately handles the complex differences between frequency bands. For 900MHz/Dual-Band devices, it actively injects your chosen domain (e.g., FCC, EU868) into the compiled JSON payload. For standard 2.4GHz targets, it utilizes a boolean flag to silently route the extraction process to either the standard FCC/ or European LBT/ base firmware folders during assembly.

Firmware Caching

Offline flashing is made possible through a robust local caching system. When a user downloads a release via the Firmware Manager, the FirmwareCacheService pulls the generic firmware.zip and device-specific hardware.zip directly from the ExpressLRS Artifactory. These archives are managed and stored locally on the device, ensuring assembly and flashing can occur instantly in the field without any active internet connection.

Persistent Storage

To streamline the user experience, volatile but frequently reused configuration data—such as custom Binding Phrases, Wi-Fi SSIDs, and network passwords—are securely saved to the device using SharedPreferences. This prevents users from having to repeatedly re-enter complex network credentials or binding strings every time they flash a new device.

Analytics Suite

The application integrates sentry_flutter to provide a comprehensive, opt-in crash reporting and analytics suite. This allows for real-time monitoring of unexpected runtime exceptions, flashing pipeline failures, or configuration parsing errors out in the field. It helps maintain the high reliability required for hardware-management bridging applications.

Cellular Fallback & Forced Routing

Mobile operating systems (especially newer Android and iOS versions) will automatically drop or deprioritize Wi-Fi connections that do not provide internet access, silently routing traffic over 5G/LTE instead. This causes apps to fail to connect to ELRS hardware hotspots (like 10.0.0.1).

ELRS Mobile solves this natively. When the app detects an active connection to an ELRS hotspot, the NativeNetworkService invokes a platform-specific MethodChannel (org.expresslrs.elrs_mobile/network) to execute bindProcessToWiFi. This forcibly binds the entire Flutter app process directly to the Wi-Fi interface at the OS level, guaranteeing that all HTTP requests and MDNS discovery packets reach the hardware, entirely bypassing the OS’s cellular fallback logic.