Optical flow sensor is not fusing with imu

ArduCopter
1

Hi everyone,

I’m trying to get my PMW3901 (UART version) working with ArduCopter (latest stable) for indoor position hold using optical flow and a rangefinder. However, I’m running into multiple issues:

Symptoms

  • EKF3 IMU0 stopped aiding keeps appearing in MAVProxy / Mission Planner.
  • COMMAND_ACK: NAV_TAKEOFF: FAILED is shown when I try to take off in Loiter mode.
  • I see flowX and flowY values changing, but they don’t seem to correlate with IMU.GyrX and GyrY, nor with BODY.X and BODY.Y.
  • EKF status flags do not show fusion of velocity from optical flow.

My Setup

  • Flight Controller: Flywoo GOKU GN745
  • Sensor: PMW3901 UART (connected to TX2/RX2)
  • Firmware: ArduCopter [version]
  • Companion: Raspberry Pi Zero 2 W (used for MAVProxy, not powering the sensor)

Key Parameters

  • FLOW_TYPE = 4
  • FLOW_ORIENT_YAW = 0 (tested 0, 90, 180, 270 with no luck)
  • SERIAL2_PROTOCOL = 18
  • SERIAL2_BAUD = 115
  • EK3_SRC1_VELXY = 5 (Optical Flow)
  • EK3_SRC1_POSXY = 0 (None)
  • RNGFND1_TYPE = 1 (LidarLite / Benewake etc.)
  • EK3_FLOW_DELAY = 100
  • EK3_FLOW_GATE = 3
  • AHRS_EKF_TYPE = 3

Observations

  • opt_m_x and opt_m_y change slightly when I move the drone, so the sensor seems to be alive.

  • opt_qua is below 100 most of the time.

  • No “flow fusion” is seen in EKF status (status bit 0x20 off).

  • Logs show intermittent aiding, but mostly “EKF3 IMU0 stopped aiding”.

  • I also noticed takeoff fails with NAV_TAKEOFF: FAILED when trying guided_nogps mode.

  • What exactly triggers “EKF3 IMU0 stopped aiding”? Is it a velocity gate error due to bad scale or quality?

  • Any checklist for resolving NAV_TAKEOFF: FAILED related to optical flow setup?

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