Pcb-designHow-ToIntermediate · 4 min read

How to Set Up Hardware in the Loop (HITL) in Drone Programming

To set up Hardware in the Loop (HITL) in drone programming, connect your flight controller hardware to a simulation environment that runs the drone software and simulates sensors and environment. Use a communication interface like UART or USB to link the hardware with the simulator, enabling real-time testing of flight code on actual hardware before real flights.

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Syntax

Setting up HITL involves configuring the communication between the drone's flight controller and the simulation software. The key parts include:

Flight Controller Connection: Connect via USB or UART to your computer.
Simulation Software: Runs the drone environment and sensor data.
Communication Protocol: Use protocols like MAVLink to exchange data.
Configuration Files: Set parameters to enable HITL mode in both hardware and software.

pseudo

hitl_setup {
  connect_flight_controller(port: "/dev/ttyUSB0", baudrate: 115200)
  enable_simulation(environment: "Gazebo", sensors: ["GPS", "IMU"])
  set_communication_protocol(protocol: "MAVLink")
  configure_parameters({
    hitl_mode: true,
    sensor_input: "hardware",
    actuator_output: "hardware"
  })
  start_simulation()
}

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Example

This example shows how to set up HITL using PX4 flight stack with Gazebo simulator and a Pixhawk flight controller connected via USB.

bash

# Connect Pixhawk to computer via USB
# Start PX4 SITL with HITL mode enabled
make px4_sitl gazebo HITL=1

# In another terminal, monitor MAVLink messages
mavlink_shell /dev/ttyUSB0

# PX4 firmware automatically switches to HITL mode and uses real hardware for actuators
# Gazebo simulates sensors and environment

Output

INFO [simulator] HITL mode enabled INFO [mavlink] Connected to /dev/ttyUSB0 at 115200 baud INFO [commander] Flight controller ready

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Common Pitfalls

Wrong Port or Baudrate: Using incorrect USB port or baudrate causes connection failure.
Not Enabling HITL Mode: Forgetting to set HITL flag in simulation disables hardware interaction.
Power Issues: Flight controller must be powered properly; USB alone may not suffice.
Firmware Mismatch: Simulator and hardware firmware versions must be compatible.
Ignoring Safety: Always test with props removed to avoid accidents during HITL testing.

bash

# Wrong way: Missing HITL flag
make px4_sitl gazebo

# Right way: Enable HITL
make px4_sitl gazebo HITL=1

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Quick Reference

Step	Description	Command/Action
1	Connect flight controller to PC	Use USB or UART cable
2	Enable HITL mode in simulator	Add HITL=1 flag in PX4 SITL command
3	Start simulation environment	Run Gazebo or other simulator
4	Verify communication	Check MAVLink connection on correct port
5	Test flight code with hardware	Monitor logs and actuator response

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Key Takeaways

Connect your flight controller hardware to the simulator using USB or UART with correct settings.

Enable HITL mode explicitly in your simulation software to link hardware and simulated sensors.

Ensure firmware versions on hardware and simulator match to avoid compatibility issues.

Always test HITL setups with safety precautions like removing propellers.

Use MAVLink protocol for reliable communication between hardware and simulation.