Hardware in the Loop Simulation (HITL)
Hardware-in-the-Loop (HITL) is a simulation mode in which normal PX4 firmware is run on real flight controller hardware. This approach has the benefit of testing most of the actual flight code on the real hardware.
PX4 supports HITL for multicopters (using jMAVSim or Gazebo) and fixed wing (using Gazebo or X-Plane demo/full version).
The current list of compatible airframes vs Simulators is:
|HIL Quadcopter X||1001||Y||Y|
|Generic Quadrotor x copter||4001||Y||Y|
|DJI Flame Wheel f450||4011||Y||Y|
HITL Simulation Environment
With Hardware-in-the-Loop (HITL) simulation the normal PX firmware is run on real hardware. QGroundControl is connected to the physical hardware over USB and acts as a gateway to forward data between the simulator running on a development computer, PX4, and any offboard API.
The diagram below shows a typical HITL simulation environment:
- A HITL configuration is selected (via QGroundControl) that doesn't start any real sensors.
- QGroundControl is connected to the flight controller via the USB.
- QGroundControl is connected to the simulator and offboard API via UDP.
- A serial connection is used to connect Joystick/Gamepad hardware via QGroundControl.
For more information see: Simulation.
HITL vs SITL
SITL runs on a development computer in a simulated environment, and uses firmware specifically generated for that environment. Other than simulation drivers to provide fake environmental data from the simulator the system behaves normally.
By contrast, HITL runs normal PX4 firmware in "HITL mode", on normal hardware. The simulation data enters the system at a different point than for SITL. Core modules like commander and sensors have HIL modes at startup that bypass some of the normal functionality.
In summary, HITL runs PX4 on the actual hardware using standard firmware, but SITL actually executes more of the standard system code.
Setting up HITL
- Connect the autopilot directly to QGroundControl via USB.
Enable HITL Mode
- Open Setup > Safety section.
Enable HITL mode by selecting Enabled from the HITL Enabled list:
- Open Setup > Airframes
Select a compatible airframe you want to test. Generally you'll select HILStar for Fixed Wing/X-Plane simulator and a HIL QuadCopter option for copters (and jMAVSim or Gazebo).
Under the General tab of the settings menu, uncheck all AutoConnect boxes except for UDP.
(Gazebo only) Set the
921600(see PX4 User Guide > Parameters for instructions on how to change parameters).
(Optional) Configure Joystick and Failsafe.
Set the following parameters in order to use a joystick instead of an RC remote control transmitter:
- COM_RC_IN_MODE to "Joystick/No RC Checks". This allows joystick input and disables RC input checks.
- NAV_DLL_ACT to "Disabled". This ensures that no RC failsafe actions interfere when not running HITL with a radio control.
Once configuration is complete, close QGroundControl and disconnect the flight controller hardware from the computer.
Follow the appropriate setup steps for your simulator in the following sections.
Make sure QGroundControl is not running!
- Update the environment variables:
cd <Firmware_clone> make posix_sitl_default gazebo source Tools/setup_gazebo.bash $(pwd) $(pwd)/build/posix_sitl_default
- Open the vehicle model's sdf file (e.g. Tools/sitl_gazebo/models/iris/iris.sdf).
mavlink_interface pluginsection, change the
/dev/ttyACM0) if necessary.
The serial device depends on what port is used to connect the vehicle to the computer (this is usually
/dev/ttyACM0). An easy way to check on Ubuntu is to plug in the autopilot, open up a terminal, and type
dmesg | grep "tty". The correct device will be the last one shown.
Connect the flight controller to the computer and wait for it to boot.
- Run Gazebo in HITL mode
- Start QGroundControl. It should autoconnect to PX4 and Gazebo.
jMAVSim (Quadrotor only)
Make sure QGroundControl is not running!
- Run jMAVSim in HITL mode (replace the serial port name
/dev/ttyACM0if necessary - e.g. on Mac OS this would be
./Tools/jmavsim_run.sh -q -d /dev/ttyACM0 -b 921600 -r 250
- Start QGroundControl. It should autoconnect to PX4 and jMAVSim.
Using X-Plane (Fixed Wing only)
X-Plane is currently not recommended. Among other issues, the frame update rate is too slow to run the system realistically.
To set up X-Plane:
- Open X-Plane
In Settings > Data Input and Output, set these checkboxes:
In Settings > Net Connections, in the Data tab, set localhost and port 49005 as IP address, as shown below:
Enable X-Plane HITL in QGroundControl:
- Open QGroundControl
Open Widgets > HIL Config. Select X-Plane 10 in the drop-down and hit connect. Once the system is connected, battery status, GPS status and aircraft position should all become valid:
Fly an Autonomous Mission in HITL
You should not be able to use QGroundControl to run missions and otherwise control the vehicle.