How to install an optical flow positioning module

Installing an optical flow positioning module involves mounting the sensor, connecting it to the flight controller, flashing compatible firmware, and configuring software parameters for accurate position and velocity tracking.

Hardware Installation

1. Mount the Sensor: Attach the optical flow module (e.g., PX4Flow, LiteWing PMW3901MB, Here Flow) to the bottom of the drone, ensuring the camera faces downward and has a clear, unobstructed view of the ground . Use 3M adhesive or vibration-isolating mounts if recommended. Ensure sufficient clearance from the ground using landing gear to avoid interference during takeoff .

2. Connect to Flight Controller: Depending on the module, connect via UART, I2C, MAVLink, or CAN bus. For example, Here Flow uses a 4-pin CAN cable, while PX4Flow can connect via micro USB or UART . Ensure the sensor receives power either from the USB connection or the drone battery .

3. Optional Rangefinder: For accurate altitude measurements, pair the optical flow sensor with a LiDAR or sonar rangefinder (e.g., LightWare SF10b, SF11B) as many optical flow modules do not reliably measure height alone .

Firmware and Software Setup

1. Firmware Flashing: Connect the sensor to a computer and use the appropriate software (Mission Planner, QGroundControl, or MicroAssistant) to load the module-compatible firmware . For PX4Flow, select the px4flow binary and follow the firmware upload instructions. For Here Flow, enable CAN and rangefinder parameters in Mission Planner.

2. Parameter Configuration: After flashing, configure the flight controller parameters:

   • Enable optical flow: e.g., FLOW_TYPE = 6 for Here Flow .
   • Set rangefinder type and limits: e.g., RNGFND_TYPE = 24, RNGFND_MAX_CM = 200, RNGFND_MIN_CM = 5 .
   • If using PX4, configure EKF2 parameters for optical flow fusion (EKF2_OF_CTRL) and set sensor offsets if the module is not at the vehicle center .

3. Software Integration: In iNav or PX4, assign the correct UART/port and protocol (MSP, MAVLink) for the sensor . Save and reboot the flight controller to apply changes.

Calibration and Testing

1. Focus and Alignment: Adjust the lens focus (PX4Flow) or ensure the camera is properly aligned to the ground .
2. Preflight Checks: Remove propellers for safety, power the drone, and verify that the optical flow and rangefinder readings change when moving the drone or adjusting altitude .
3. Data Verification: Check that the sensor outputs (e.g., opt_m_x, opt_m_y) respond correctly to movement. If not, recheck wiring, parameters, or reboot the flight controller .

Software Development (Optional)

For modules like LiteWing PMW3901MB, ensure your development environment is ready with Python, required libraries, and a CRTP link to the drone. This allows reading velocity and position data in real time for custom scripts or autonomous flight projects .

By following these steps, your optical flow positioning module will be properly installed, calibrated, and ready to provide stable position hold and velocity estimation for your drone.