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

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Introduction to ExpressLRS for Fixed Wings

ExpressLRS (ELRS) is a popular open-source radio control link known for its low latency, long range, and robust performance. While many pilots use it with digital outputs like CRSF, some fixed-wing setups still rely on PWM outputs to connect to their flight controllers or servos. This guide will walk you through setting up ExpressLRS on a fixed-wing aircraft using PWM outputs, perfect for UK hobbyists and makers wanting a reliable and modern RC system.

What You’ll Need

  • An ExpressLRS compatible transmitter module (TX module) or a full radio with ELRS support.
  • An ExpressLRS receiver (RX) that supports PWM output.
  • A fixed-wing aircraft with a flight controller or direct servo connections that accept PWM inputs.
  • A computer with the ExpressLRS Configurator software installed.
  • A USB cable to flash the firmware on your ELRS TX module and RX.

Step 1: Flashing the ExpressLRS Firmware

Before you can use ELRS, you need to flash the correct firmware on both your transmitter module and receiver. Here's how:

  1. Download and install the latest ExpressLRS Configurator from the official GitHub page.
  2. Connect your TX module or radio to your PC via USB.
  3. Select your device in the Configurator and pick the correct target and build options (for fixed-wing, choosing the appropriate frequency band – 2.4 GHz is common in the UK).
  4. Build and flash the firmware to your TX module.
  5. Repeat the process for your receiver, making sure to select the PWM output option during the build if available.

Step 2: Connecting Your Receiver with PWM Outputs

Once flashed, you need to wire your receiver to your flight controller or servos using PWM signals. Most ELRS receivers provide multiple PWM channels via servo-style connectors. Here’s how to proceed:

  • Identify the PWM output pins on your receiver. Usually, these are standard servo connectors labelled CH1, CH2, etc.
  • Connect each PWM channel from the receiver to the corresponding input on your flight controller or directly to servos if you’re not using a flight controller.
  • Make sure to connect the ground (GND) and power (usually 5V) lines properly to avoid damage.

Example wiring:

  • CH1 (Throttle) → Flight Controller Throttle Input or ESC
  • CH2 (Aileron) → Flight Controller Aileron Input or Aileron Servo
  • CH3 (Elevator) → Elevator Input
  • CH4 (Rudder) → Rudder Input

Step 3: Binding the Receiver and Transmitter

Binding pairs your TX module and RX so they communicate securely. To bind:

  1. Power on your receiver in bind mode (usually by holding a bind button or powering with a bind jumper).
  2. On your transmitter, enter the binding menu and start the bind process.
  3. Once bound, the receiver LED should indicate a successful connection.

Step 4: Configuring Your Flight Controller

If you use a flight controller, configure it to accept PWM inputs from the ELRS receiver:

  • Connect your flight controller to your PC and open your preferred configurator software (e.g., Betaflight, INAV).
  • Set the receiver mode to PWM.
  • Assign the channels according to your wiring.
  • Test the control surfaces or motor outputs to ensure they respond correctly.

Tips for a Smooth Setup

  • Use quality servo cables and connectors to avoid signal loss.
  • Double-check your wiring before powering up to prevent shorts.
  • Keep your firmware versions up to date for best performance.
  • Test your setup on the bench before flying to avoid surprises.

Conclusion

Setting up ExpressLRS with PWM outputs on a fixed-wing aircraft is a straightforward way to enjoy the benefits of ELRS while maintaining compatibility with traditional PWM-based flight controllers and servos. With careful flashing, wiring, and configuration, you’ll have a reliable and responsive control link ready for your next flight.

Happy flying and tinkering!

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