The ER4 is part of RadioMaster’s revolutionary “ER” series, specifically built to modernize traditional RC models.5 Unlike standard 2.4GHz receivers that can suffer from signal “brown-outs” in urban areas, the ER4 uses LoRa modulation (via ExpressLRS) to provide a robust link that far exceeds the visual line of sight.
Installation is “Plug-and-Play” for anyone coming from older systems. It supports Wi-Fi updates, meaning you can flash the latest firmware or change settings via a web browser on your phone—no specialized USB dongles required.7 The dedicated EXT-V solder pad allows you to monitor your flight battery voltage directly on your transmitter, providing a critical safety layer for electric gliders and park flyers.
Key Performance Highlights:
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ExpressLRS 3.3.0 Ready: Pre-installed with the latest ELRS protocol for ultra-low latency and “locked-in” control feel.
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Integrated Voltage Telemetry: A single wire soldered to the EXT-V pad allows you to monitor batteries up to 8S (35v) in real-time.
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Compact “Flyweight” Design: At 30x15mm, it fits easily into micro-DLGs (Discus Launch Gliders), 1/24 scale crawlers, or small foamies.
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Dual Power Logic: Automatically detects if you are using the EXT-V pad for battery telemetry or if it should report the 5V rail voltage from the receiver pins.
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Wi-Fi Configuration: Access the “WebUI” by letting the RX sit for 60 seconds (or using the LUA script) to update binding phrases and firmware wirelessly.
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High-Sensitivity Antenna: The 15cm wire antenna provides excellent spatial diversity, allowing for flexible mounting inside carbon or foam fuselages.
Technical Specifications:
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Protocol: ExpressLRS 2.4GHz
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Channels: 4 PWM Outputs
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Telemetry Power: 10mW
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Voltage Detection Range: DC 4.0V – 35V
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Power Supply: DC 4.5V – 8.4V (2S LiPo compatible)
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Weight: 3.0g
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Dimensions: 30 x 15 x 5 mm
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Antenna: 150mm High-Sensitivity
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Firmware Target: RadioMaster ER4 2400 PWM RX





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