How to Set Up ExpressLRS on a Fixed Wing with PWM Outputs

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Introduction

If you're a UK-based RC pilot or maker looking to upgrade your fixed-wing aircraft's radio system, ExpressLRS (ELRS) is an excellent choice. Known for its low latency, long range, and open-source flexibility, ELRS has become a favourite among hobbyists and DIY enthusiasts. This guide will walk you through setting up ExpressLRS on your fixed wing using PWM outputs, which is ideal if your flight controller or receiver doesn't support native CRSF or serial protocols.

What You’ll Need

Before we dive in, make sure you have the following:

  • A fixed-wing aircraft with a flight controller that supports PWM inputs
  • An ExpressLRS receiver module (ELRS RX) with PWM output pins
  • An ExpressLRS compatible transmitter module or radio with ELRS firmware
  • A USB cable and a computer for flashing firmware
  • Basic tools like a soldering iron, wire cutters, and a multimeter

Step 1: Flashing the Firmware

The first step is to flash the latest ExpressLRS firmware onto both your transmitter module and receiver. Visit the https://github.com/ExpressLRS/ExpressLRS" target="_blank">ExpressLRS GitHub page and download the ExpressLRS Configurator tool.

Follow these steps:

  • Connect your transmitter module to your computer using USB.
  • Open the ExpressLRS Configurator and select your transmitter module model.
  • Choose the latest stable firmware version and configure your RF settings (frequency, power, etc.) suitable for the UK regulations.
  • Flash the firmware to your transmitter module.
  • Repeat the process for the receiver, connecting it via USB or through a USB-to-serial adapter.

Step 2: Wiring the Receiver to the Flight Controller

Since your fixed wing uses PWM outputs, the ELRS receiver will output standard PWM signals for each channel. Here’s how to wire it:

  • Identify the PWM output pins on your ELRS receiver (usually labelled CH1, CH2, etc.).
  • Connect each PWM output wire to the corresponding PWM input on your flight controller.
  • Make sure to connect the receiver’s ground (GND) and 5V (or 3.3V depending on your RX) pins to the flight controller’s power and ground.

Tip: Use a multimeter to verify voltage levels and continuity to avoid damage.

Step 3: Configuring the Flight Controller

Power up your flight controller and connect it to your computer. Open your flight controller configuration tool (e.g., Betaflight Configurator or INAV Configurator).

  • Navigate to the input or receiver tab.
  • Select "PWM" as the receiver protocol.
  • Verify that the channels respond correctly as you move sticks or switches on your transmitter.
  • If channels are reversed or out of order, adjust the channel mapping accordingly.

Step 4: Binding Your Radio and Testing

Binding pairs your transmitter with the receiver to communicate securely.

  • Put your transmitter module into bind mode via the ExpressLRS Configurator or hardware button.
  • Power up the receiver in bind mode (usually holding a button while powering on).
  • Wait for the LEDs to indicate a successful bind (typically a solid LED).

Once bound, test the control surfaces on your fixed wing (ailerons, elevator, rudder) to ensure they move correspondingly.

Final Tips

  • Always check UK radio frequency regulations to ensure compliance.
  • Keep firmware up to date for best performance and security.
  • Secure your wiring to prevent vibration-related issues during flight.
  • Consider using heat shrink tubing or servo connectors for neat and reliable connections.

Conclusion

Setting up ExpressLRS on a fixed wing with PWM outputs is a straightforward way to enjoy long-range, low-latency control with your existing flight controller. With just a bit of firmware flashing, wiring, and configuration, you can upgrade your fixed wing’s radio system and take advantage of one of the most advanced RC link technologies available today. Happy flying!

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