Pixhawk Setup

Pixhawk Setup

The Pixhawk takes care of the low-level control in the ACSL Ecosystem, namely, sensor fusion and controlling the motors. We recommend using Pixhawk 6C for performance-related issues. This section deals with flashing the latest PX4-Autopilot firmware onto the board and setting it up for three sensor fusion methods.

1. Compiling the Firmware

Before compiling the firmware, please set up the toolchain following the instructions here.

Note

Make sure you set up the toolchain for your specific operating system.

Tip

It is recommended to compile this on Ubuntu for a smooth process. Windows and macOS have some idiosyncrasies that are best to avoid.

To compile the firmware, we need to clone the latest version from the PX4-Autopilot Github.

git clone --recurse-submodules https://github.com/PX4/PX4-Autopilot.git

Tip

As of the time of writing, the main branch of the PX4-Autopilot repository corresponds to the latest v1.16.x release. If you ever need to roll back to a previous version due to a bug or issue, you can check the repository's tags to select a specific release. Once you've identified the desired version, simply run:

git clone --branch <tag-moniker> --recurse-submodules https://github.com/PX4/PX4-Autopilot.git

It is recommended to roll back to v1.15.4 if there are any issues.

Once the toolchain is set up and the repository is cloned, navigate to the root folder of the cloned repository

cd <path-to-repo>/PX4-Autopilot

Compile the firmware for the Pixhawk that is specific to the Pixhawk version by running the command from the table below.

Note

We use the Pixhawk 6C, therefore the compile command will be

make px4_fmu-v6c_default

Flight Controller	FMU Version	PX4 Build Command
Holybro Pixhawk 6X-RT	FMUv6X	make px4_fmu-v6xrt_default
Holybro Pixhawk 6X	FMUv6X	make px4_fmu-v6x_default
Holybro Pixhawk 6C	FMUv6C	make px4_fmu-v6c_default
Holybro Pixhawk 6C Mini	FMUv6C	make px4_fmu-v6c_default
Holybro Pix32 v6	FMUv6C	make px4_fmu-v6c_default
Holybro Pixhawk 5X	FMUv5X	make px4_fmu-v5x_default
Pixhawk 4	FMUv5	make px4_fmu-v5_default
Pixhawk 4 Mini	FMUv5	make px4_fmu-v5_default
CUAV V5+	FMUv5	make px4_fmu-v5_default
CUAV V5 nano	FMUv5	make px4_fmu-v5_default
Pixracer	FMUv4	make px4_fmu-v4_default
Pixhawk 3 Pro	FMUv4pro	make px4_fmu-v4pro_default
Pixhawk Mini	FMUv3	make px4_fmu-v3_default
Pixhawk 2 (Cube Black)	FMUv3	make px4_fmu-v3_default
mRo Pixhawk (2MB Flash)	FMUv3	make px4_fmu-v3_default
Holybro pix32	FMUv2	make px4_fmu-v2_default
Pixfalcon	FMUv2	make px4_fmu-v2_default
Dropix	FMUv2	make px4_fmu-v2_default
Pixhawk 1	FMUv2	make px4_fmu-v2_default
Pixhawk 1 (2 MB flash)	FMUv3	make px4_fmu-v3_default

Tip

It is recommended that you pick a Pixhawk with firmware version fmu-v5 and above.

Finally, plug in the Pixhawk and upload the firmware to the Pixhawk by appending upload to the command you picked above. For example, Pixhawk 6C will need the command

make px4_fmu-v6c_default upload

A successful upload should give an output similar to this

Erase  : [====================] 100.0%
Program: [====================] 100.0%
Verify : [====================] 100.0%
Rebooting.

[100%] Built target upload

2. Initial Setup

This section describes how to set up the Flight Controller (Pixhawk 6c) for use with a UAV. This initial setup section deals with setting up the type of vehicle or frame in section 2.1, setting up and claibrating the onboard imu in section 2.2, setting up the radio with the kill-switch and the flight modes in section 2.3 and finally setting up the actuators and calibrating them in section 2.4.

Note

Please note that the instructions in this section are provided for the QRBP (Quad Rotor Biplane). The instructions for choosing a different frame are very similar. If a different frame is picked, the actuators should be configured to spin in that particular frame's orientation at the hardware level. Software switching of the actuator direction of rotation is not recommended.

2.1 Setting up the frame

After successfully flashing the firmware onto your Pixhawk, you need to configure the airframe before proceeding with any further setup.

1. Connect the Pixhawk
   Use a USB‑C cable to connect the Pixhawk to your ground station.
   If you just compiled and flashed the firmware, disconnect and reconnect the Pixhawk to ensure a clean connection.

2. Launch QGroundControl
   Open QGroundControl on your ground station while the Pixhawk is connected. The software should automatically detect the flight controller.

3. Follow the Airframe Setup Guide
   Once connected, follow the detailed instructions provided in the official PX4 documentation:
   👉 PX4 Airframe Configuration Guide

This process allows you to assign the correct frame type (e.g., quadcopter, X8, hexacopter) and ensures that all motor outputs and flight parameters align with your physical UAV configuration.
Completing this step is essential for stable flight performance and correct controller mapping within the ACSL Flightstack.

2.2 Sensor Setup and Calibration

Once your Pixhawk has been connected and the airframe configured, the next step is to calibrate all onboard sensors using QGroundControl. Sensor calibration ensures accurate flight data, stable control behavior, and proper navigation — all of which are critical for flight safety.

IMPORTANT
Calibration should be performed whenever a sensor is replaced, the flight controller is remounted, or external conditions (such as temperature) have shifted significantly.

2.2.1 🧭 Overview

QGroundControl guides the user through the calibration of each sensor step‑by‑step. The main sensors that require calibration during first‑time setup are:

• Accelerometer
• Gyroscope
• Compass (Magnetometer)

Each of these sensors provides specific flight data for orientation, position, and stabilization. Proper calibration ensures consistent performance during flight.

2.2.2 🪫 Accelerometer Calibration

The accelerometer measures the linear acceleration of the aircraft on its three axes and helps determine attitude when combined with gyroscope data.

Steps:

1. Open QGroundControl and connect your vehicle.
2. Select Vehicle Setup → Sensors.
3. Click Accelerometer to begin calibration.
4. Follow the on‑screen instructions to position the vehicle in each orientation shown.
5. Hold the vehicle still until each orientation turns green in QGroundControl.
6. When all positions are complete, the progress bar and all orientation images will indicate Calibration complete.

Note

The accelerometer calibration uses a least‑squares algorithm — exact 90‑degree orientations are not required, but the vehicle must remain still in each position.

For more details, see the official PX4 documentation on Accelerometer Calibration.

2.2.3 🔄 Gyroscope Calibration

The gyroscope measures rotational rate and is essential for stabilizing the vehicle in flight.

Steps:

1. In QGroundControl, navigate to Vehicle Setup → Sensors.
2. Select Gyroscope.
3. Place the vehicle on a flat, stable surface.
4. Click OK to start calibration.
5. Keep the vehicle completely still until calibration completes.

Tip

If the vehicle is moved during calibration, QGroundControl will automatically restart the process.

For official instructions, refer to Gyroscope Calibration.

2.2.4 🧲 Compass (Magnetometer) Calibration

The compass (or magnetometer) measures the Earth’s magnetic field to determine the UAV’s heading. This calibration is crucial for correct yaw orientation and GPS navigation.

Steps:

1. In QGroundControl, go to Vehicle Setup → Sensors.
2. Select Compass.
3. Follow the on‑screen prompts to rotate the vehicle slowly along multiple axes.
4. The software will indicate success once all required orientations are calibrated.

Caution

Perform compass calibration outdoors, away from metallic objects or electromagnetic interference (benches, laptops, power lines, etc.).

Further information can be found in the Compass Calibration Guide.

2.2.5 ✅ Final Check

Once all sensors are calibrated:

• Ensure QGroundControl shows green indicators for each sensor.
• Power‑cycle the flight controller to save all changes.
• Verify that the Horizon Level and Compass Heading appear correct before arming.

Proper sensor calibration is the foundation of a stable and reliable ACSL Flightstack‑based system. Performing it carefully ensures optimal flight performance and safe operation.

2.3 Radio Setup and Flight Modes

Before performing any manual or autonomous flight, it is important to set up and calibrate your radio control (RC) system and verify that all flight modes are correctly assigned in QGroundControl (QGC). Proper configuration ensures safe, reliable, and responsive control during both test and mission flights.

2.3.1 Binding the Receiver

Before calibrating the radio, ensure the transmitter and receiver are bound according to the manufacturer’s instructions. Each radio manufacturer uses different binding procedures — refer to your RC system's manual for exact steps.

Typical binding steps:

1. Power on the aircraft or connect the receiver to the Pixhawk.
2. Place the receiver in bind mode (option in QGroundControl or a button on the receiver).
3. Power on the transmitter and activate its binding function.
4. Wait until both devices indicate a successful link.

2.3.2 Performing the Calibration

Follow these steps in QGroundControl:

1. Open QGroundControl and connect your vehicle via USB.
2. Select the Gear icon → Vehicle Setup → Radio tab.
3. Click OK to begin calibration.
4. Move each stick as indicated on the on‑screen transmitter diagram — including full-range movements for throttle, roll, pitch, and yaw.
5. When prompted, move all switches and knobs through their entire range (you can observe changes in the Channel Monitor).
6. Press Next when finished to save your calibration.

Tip

Ensure sticks and switches return to their normal positions after calibration. You can revisit this menu anytime to verify channel outputs before flight.

For detailed guidance, consult the official PX4 Radio Control Setup Guide.

2.3.3 🕹️ Flight Mode Configuration

Flight modes define how the autopilot interprets control inputs and behaves under certain conditions. These modes can range from full manual control to complete autonomy.

PX4 supports assigning up to six flight modes using a single mode channel (typically linked to a toggle or 3‑way switch on the transmitter).

Configuration Procedure:

1. With the transmitter powered on, open QGroundControl and go to
   Vehicle Setup → Flight Modes.
2. Select the Mode Channel (usually Channel 5, 6, 7, or 8, depending on your radio).
3. Assign the modes as follows:

Mode Slot	Flight Mode	Description
1–2	Manual	Direct pilot control with no stabilization
3–4	Stabilized	Autopilot assists with roll and pitch leveling
5–6	Offboard	Vehicle responds to external commands from a companion computer or GCS

4. Move your transmitter’s mode switch to verify each position triggers the correct mode. The active mode will be highlighted (yellow) in QGroundControl.
5. Confirm mode switching in the Channel Monitor, ensuring the values change consistently.

Note

A 3‑way switch is required for proper mode selection. Radios without this feature will need a workaround (e.g., combining two smaller switches) to enable access to all assigned modes — particularly Offboard flight.

For additional configuration details, refer to the official PX4 Flight Mode Setup Guide.

Tip

Our configuration uses the Spektrum DX9 transmitter paired with a compatible DSMX receiver connected via the DSM port on the Pixhawk. The DX9 offers a simple and stable setup process, and binding can be performed directly within QGroundControl using the Spektrum Bind feature.

This configuration is widely recommended because it allows for quick calibration, reliable channel mapping, and fully supports 3‑way switch mode selection, making it one of the easiest and most reliable radio setups for use with PX4 and ACSL Flightstack.

2.4 Power and Actuator Setup and Calibration

Proper configuration of actuators, ESCs, and motor outputs is critical to ensure correct motor direction, control responsiveness, and system safety. The following steps outline the general procedure using QGroundControl. Exact details may vary slightly depending on your platform configuration and vehicle type.

2.4.1 ⚙️ Actuator Setup

In this step, the actuator outputs are assigned and tested.

Procedure:

1. Open QGroundControl and navigate to
   Vehicle Setup → Actuators.
2. Verify that the correct geometry is shown for your selected airframe (e.g., quadcopter, X8, or fixed‑wing).
3. Map motors, servos, and other control actuators to the appropriate output channels.
4. Test each actuator using the Actuator Testing section to confirm movement and direction.

Note

Only mapped outputs are active. Ensure all outputs correspond to the flight configuration of your selected airframe.

For detailed information, refer to the PX4 Actuator Configuration Guide.

2.4.2 🔌 ESC Calibration

Electronic Speed Controller (ESC) calibration ensures that all motors respond consistently to throttle commands.
This procedure must always be done without propellers attached.

Procedure:

1. Remove all propellers.
2. In QGroundControl, go to Settings → Power.
3. Press Calibrate and follow the on‑screen prompts.
4. When instructed, power the ESCs by connecting the battery — calibration will begin automatically.
5. Wait until the ESCs complete their beeping sequence and calibration is confirmed.
6. Disconnect the battery when prompted.

Caution

Never perform ESC calibration with propellers attached. Motors may spin unexpectedly at full speed.

For additional information, see the PX4 ESC Calibration Guide.

2.4.3 🧭 Motor and ESC Verification

After configuration and calibration, validate the motor direction, order, and individual response.

Procedure:

1. Navigate to Vehicle Setup → Motors in QGroundControl.
2. Enable motor testing (safety switch must be pressed if available).
3. Spin each motor individually to ensure:
   • The motor spins in the correct direction.
   • The motor order matches the frame diagram.
4. Adjust wiring of the ESC if necessary, do not use software to switch the motor direction.

Caution

If using DShot ESCs, motor direction can be reversed via software commands — do not use this feature for ACSL Flightstack setups. Always ensure correct motor direction through wiring.

You can find in‑depth details in the PX4 ESCs and Motors Guide.

3. Parameter Settings

After setting up and calibrating the sensors, actuators, radio, flight modes and battery, we can proceed to set up the parameters.

Parameters are present in vehicle info-> Parameters in the QGroundcontrol app, as shown below

Figure 6: Go to Parameters Tab on QGroundcontrol

Tip

Please see the image below if you are asked to reboot the Pixhawk after a parameter is set

Figure 7: How to Reboot Pixhawk

Some parameters that are common for all three modes are to be set as follows:

To ensure proper operation in Offboard mode and set up communication with ROS2 via an ODroid, configure the following PX4 parameters.

Auto-Disarm Prevention and Arm Switch Configuration

Parameter	Value	Explanation
COM_DISARM_PRFLT	-1.0	Prevents automatic disarming while waiting in Offboard mode. Any negative value disables the preflight disarm timeout.
COM_DISARM_LAND	-1.0	Prevents automatic disarming after landing (or false detection of landing).
COM_ARM_SWISBTN	Enabled	Enables use of a momentary switch for arming the vehicle.

ROS2 Communication Setup (Pixhawk ↔ Odroid)

Parameter	Value	Explanation
UXRCE_DDS_CFG	TELEM 2	Sets the XRCE-DDS communication interface to use TELEM 2 for ROS2.
SER_TEL2_BAUD	921600 8N1	Sets the baud rate and serial format for TELEM 2.
MAV_1_CONFIG	Disabled	Disables MAVLink on port 1 to free up resources or avoid conflicts.
MAV_2_CONFIG	Disabled	Disables MAVLink on port 2 for the same reason.

Warning

After setting the UXRCE_DDS_CFG parameter, make sure to reboot the vehicle for changes to take effect.

3.1 MOCAP Configuration

PX4 EKF2 and Sensor Configuration for MOCAP-Sensor Fused Positioning

Use the following parameter settings to configure the PX4 system for mocap sensor fused positioning without relying on GPS or magnetometers. These settings are especially useful for indoor or GPS-denied environments.

Sensor and System Configuration

Parameter	Value	Explanation
SYS_HAS_GPS	Disabled	Disables GPS to avoid attempting fusion with GPS data.
SYS_HAS_MAG	0	Disables use of magnetometer.
UAVCAN_ENABLE	Disabled	Disables UAVCAN (used for CAN-based peripherals).

EKF2 Configuration for Vision Input

Parameter	Value	Explanation
EKF2_HGT_REF	Vision	Uses vision-based height reference for altitude estimation.
EKF2_EV_CTRL	11	Enables use of external vision for position and velocity.
EKF2_MAG_TYPE	Automatic	Lets EKF choose whether or not to use magnetometer data.
EKF2_RNG_CTRL	Disable range fusion	Disables rangefinder data in EKF fusion.
EKF2_TAU_POS	0.1	Vision position data time constant (lower = faster adaptation).
EKF2_TAU_VEL	0.1	Vision velocity data time constant.
EKF2_EVP_NOISE	0.01	Noise value for vision position observation.
EKF2_EVV_NOISE	0.01	Noise value for vision velocity observation.
EKF2_EVA_NOISE	2.87	Noise value for vision acceleration observation.
EKF2_EV_NOISE_MD	Default	Mode for adjusting vision noise (leave as default unless tuning).

Note

Reference : PX4 EKF2 Tuning Guide

3.2 VIO Configuration

PX4 EKF2 and Sensor Configuration for VIO-Sensor Fused Positioning

Use the following parameter settings to configure the PX4 system for VIO sensor fused positioning without relying on GPS or magnetometers. These settings are especially useful for indoor or GPS-denied environments.

Sensor and System Configuration

Parameter	Value	Explanation
SYS_HAS_GPS	Disabled	Disables GPS to avoid attempting fusion with GPS data.
SYS_HAS_MAG	0	Disables use of magnetometer.
UAVCAN_ENABLE	Disabled	Disables UAVCAN (used for CAN-based peripherals).

EKF2 Configuration for Vision Input

Parameter	Value	Explanation
EKF2_HGT_REF	Vision	Uses vision-based height reference for altitude estimation.
EKF2_EV_CTRL	11	Enables use of external vision for position and velocity.
EKF2_MAG_TYPE	Automatic	Lets EKF choose whether or not to use magnetometer data.
EKF2_RNG_CTRL	Disable range fusion	Disables rangefinder data in EKF fusion.
EKF2_TAU_POS	NEEDS TUNING	Vision position data time constant. Tune this parameter following the PX4 EKF2 Tuning Guide.
EKF2_TAU_VEL	NEEDS TUNING	Vision velocity data time constant. Refer to the PX4 EKF2 Tuning Guide for adjustment procedure.
EKF2_EVP_NOISE	NEEDS TUNING	Noise value for vision position observation. See PX4 EKF2 Tuning Guide for tuning steps.
EKF2_EVV_NOISE	NEEDS TUNING	Noise value for vision velocity observation. Tune as described in the PX4 EKF2 Tuning Guide.
EKF2_EVA_NOISE	NEEDS TUNING	Noise value for vision acceleration observation. Adjust according to PX4 EKF2 Tuning Guide.
EKF2_EV_NOISE_MD	Default	Mode for adjusting vision noise (leave as default unless tuning).

Note

Reference : PX4 EKF2 Tuning Guide

3.3 RTK GPS Configuration

PX4 EKF2 and Sensor Configuration for RTK-GPS Fused Positioning

Use the following parameter settings to configure the PX4 system for the RTK-GPS sensor connected to the CAN 1 and CAN 2 ports. These settings are especially useful for outdoor testing.

Sensor and System Configuration

Parameter	Value	Explanation
SYS_HAS_GPS	Enabled	Enables the GPS EKF modules.
SYS_HAS_MAG	1	Enables use of magnetometer.
UAVCAN_ENABLE	Sensors Automatic config	Enables UAVCAN (used for CAN-based peripherals) and sets up the nodes.
UAVCAN_PUB_RTCM	Enabled	Enables the publication of base corrections to the rover.
UAVCAN_PUB_MBD	Disabled	Disables publishing of moving baseline data RTCM.
UAVCAN_SUB_IMU	Enabled	IF present, the IMU data on the GPS module is fused by the EKF.
MAV_PROTO_VER	2	Sets the MAVLINK messaging format to MAVLINK 2, better for communication.

EKF2 Configuration for GPS-RTK Fusion

Parameter	Value/Setting	Explanation & Action
EKF2_HGT_REF	GPS	Prioritizes GPS-derived altitude over barometric sensors. Use this if GPS altitude is reliable and barometer readings drift (e.g., due to weather changes).
EKF2_MAG_TYPE	Automatic	Lets the EKF auto-detect magnetometer type (e.g., internal vs. external). Verify magnetometer calibration in Mission Planner if facing yaw issues.
EKF2_RNG_CTRL	Disabled	Disables fusion of rangefinder data. Enable only if using a terrain-relative sensor (e.g., Lidar) for precision landing.
EKF2_OF_CTRL	Disabled	Disables optical flow data fusion. Enable if using a downward-facing optical flow sensor (e.g., in GPS-denied indoor flights).

GPS Physical Offsets

Caution

GPS Position Offsets in NED Body Frame
The values for EKF2_GPS_POS_X, EKF2_GPS_POS_Y, and EKF2_GPS_POS_Z must be specified in meters relative to the Pixhawk's NED (North-East-Down) body frame.

Key Considerations:

• Units Matter: Using centimeters, inches, or other units will cause severe navigation errors.
• Coordinate System for NED FRAME:
  • +X: Forward direction from Pixhawk's perspective.
  • +Y: Right direction from Pixhawk's perspective.
  • +Z: Downward direction (below the Pixhawk).
• Measurement Tip: Get the data from the solidworks model.

Troubleshooting:
If your drone shows erratic position hold or drift:

1. Check if your HDOP and VDOP values in QGroundControl are at or below 0.8 and 1.1 respectively. If not, wait for it to center in and your GPS must go to 3D RTK GPS Lock (fixed).
2. Double-check offset signs and units.
3. Use the ekf2_innovations log to identify GPS position/velocity mismatches.
4. Go to the PX-4 Documentation for more troubleshooting tips.

Parameter	Action Required
EKF2_GPS_POS_X	Measure and input the GPS module’s X-offset (front/back) from the drone’s center in meters. Example: 0.05 for 5 cm forward.
EKF2_GPS_POS_Y	Measure and input the GPS module’s Y-offset (left/right) from the drone’s center in meters. Example: -0.03 for 3 cm left.
EKF2_GPS_POS_Z	Measure and input the GPS module’s Z-offset (up/down) from the drone’s center in meters. Example: 0.10 for 10 cm above.

GPS Noise Tuning

Parameter	Value	Explanation
EKF2_GPS_V_NOISE	0.2	Sets velocity measurement noise (standard deviation in m/s). Lower = more trust in GPS speed data.
EKF2_GPS_P_NOISE	0.2	Sets position measurement noise (standard deviation in meters). Lower = more trust in GPS location data.

Note

GPS Noise Parameters (V_NOISE and P_NOISE):

• Default Values: Both default to 0.3 in PX4. Your settings (0.2) slightly increase trust in GPS data.
• When to Adjust:
  • Decrease (e.g., 0.1) if using a high-precision GPS (e.g., RTK) in open-sky environments.
  • Increase (e.g., 0.4) if GPS signals are noisy (e.g., urban canyons in San Francisco).
• Tuning Tip: Monitor ekf2_innovations in logs. Large velocity/position innovations (residuals) indicate mismatched sensor data; adjust noise parameters to balance fusion stability.