Matek Optical Flow & Lidar Sensor 3901-L0X INAV Module

Specifications:

• Optical Flow Sensor: PMW3901
  
• Lidar Sensor: VL53L0X (Time-of-Flight)
  
• Interface: UART (Serial)
  
• Protocol: MSP (MultiWii Serial Protocol)
  
• Input Voltage: 4.5V ~ 5.5V
  
• Power Consumption: 40mA @ 5V
  
• Working Range : 8cm~200cm
  
• Working Range (Optical Flow): Best performance > 8cm height
  
• Dimensions: 36 x 12mm
  
• Weight: 2g (approx)
  
• Mounting Holes: 30.5mm standard spacing (M3)

Applications:

• Cinewhoops & Indoor FPV: Maintain perfect hover height and position while filming indoors without manual throttle management.
  
• Autonomous Warehouse Drones: Navigate aisles and hold station in GPS-dead zones using floor texture tracking.
  
• Educational Robotics: Teach PID tuning and sensor fusion concepts using INAV or ArduPilot platforms.
  
• Inspection Drones: Inspect under-bridges or ceilings where GPS is unreliable, maintaining a set distance from surfaces.

Project Evolution

• Prerequisites (The Setup): You should be comfortable with an F4 or F7 Flight Controller running INAV and have basic soldering skills. If you've mastered GPS-guided flight outdoors, you are ready for this.
  
• The Upgrade (What this unlocks): This module adds the "Indoor Loiter" capability. Your drone will go from drifting like a leaf in the wind to staying planted in mid-air inside your living room or lab. It unlocks the "Optical Flow" and "Surface" flight modes in INAV.
  
• Effort Level: Intermediate. Requires soldering 4 wires and configuring the "MSP" port in your flight controller software.
  
• Hardware Requirement: A flight controller with one spare UART (TX/RX) port.

Virtual Technician: Wiring & Safety ⚡
⚠️ Critical Warning: The VL53L0X Lidar is sensitive to sunlight interference outdoors. This sensor is optimized for Indoor Use. ⚠️ Voltage Check: Supply exactly 5V. Do not power from a 3.3V pad, as the range will degrade.

Pinout Guide (Flight Controller Connection):

• 5V (Module) ➔ 5V/VCC (FC)
• G (Module) ➔ GND (FC)
• TX (Module) ➔ RX (Spare UART on FC)
• RX (Module) ➔ TX (Spare UART on FC)

Note: Ensure you enable "MSP" on the corresponding UART in the INAV/Betaflight Ports tab.

Required Accessories (Sold Separately):

• Silicone Connecting Wires (30AWG recommended)
• F405 or F722 Flight Controller

Pacakge Included: 

1 X Matek Optical Flow & Lidar Sensor 3901-L0X INAV Module

Frequently Asked Questions (FAQ)

1. Does this sensor work with Betaflight?
   Betaflight support for Optical Flow is limited and often experimental. It is primarily designed for and works best with INAV.
2. Can I use this outdoors?
   The PMW3901 optical flow works outdoors, but the VL53L0X Lidar uses infrared light, which is easily washed out by sunlight. Outdoor performance is unreliable.
3. What is the maximum altitude for position hold?
   The Lidar (altitude) is accurate up to 2 meters. The Optical Flow (position) can work higher, but without accurate altitude data from the Lidar, position hold degrades.
4. Does it require a specific surface to work? Yes. Optical flow needs a textured surface (carpets, tiles with patterns, grass). It will fail on plain single-color floors, water, or mirrors.
5. How do I configure this in INAV?
   Connect to a UART, set the port to MSP, and in the Configuration tab, select "MSP" for both Optical Flow and Rangefinder.
6. Why is my drone drifting even with this sensor?
   Check your focus/lens cleanliness, ensure the room is well-lit, and verify the surface has texture. Also, ensure the sensor is aligned with the drone's forward direction.
7. Does it need a separate power supply?
   No, it runs off the Flight Controller's 5V rail.
8. Can I use this with ArduPilot?
   Yes, ArduPilot supports MSP Optical Flow, but setup is more complex than INAV. Ensure your ArduPilot version supports the MSP rangefinder protocol.
9. What happens if I fly higher than 2 meters?
   The Lidar will stop providing valid readings. The flight controller typically switches to the Barometer, which is less precise for altitude hold.
10. Is this sensor plug-and-play?
    No, it requires soldering to a UART port and configuration in the ground control software.
11. Does it work in the dark?
    No. The PMW3901 is a camera; it needs light to see the floor texture.
12. Can I use this for obstacle avoidance?
    No. This is a downward-facing sensor for position stabilization, not for detecting walls or forward obstacles.
13. What is the update rate?
    It typically outputs data at roughly 10-50Hz depending on the protocol settings.
14. Does it interfere with my VTX or Receiver?
    No, it uses a digital UART interface and does not emit RF noise.
15. How do I mount it?
    It has standard mounting holes. It must be mounted facing down, with the arrow pointing towards the front of the drone.
16. Will it work on a bumpy flight?
    Excessive vibration can blur the optical flow image. Soft mounting or ensuring balanced props is recommended.
17. Can I extend the wires?
    Yes, but for UART communication, keep wires under 20-30cm to avoid signal degradation, or use shielded cables.
18. Is the lens focus adjustable?
    The lens comes factory focused. Do not attempt to rotate it unless you know exactly what you are doing, as it is glued in place.
19. What is the "Rangefinder" in the settings?
    "Rangefinder" refers to the VL53L0X Lidar component of this module, which measures the distance to the ground.
20. Why does the Lidar read 0?
    If the Lidar reads 0, it might be out of range (too far or too close <1cm) or the protective cover (if any) hasn't been removed.