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Optical Flow Setup Guide — ArduPilot / PX4 / INAV

One guide for the whole MTF family: the MTF-01, MTF-01P, and MTF-02 / MTF-02P all configure identically — wire the sensor to a spare UART, match the sensor's protocol to your firmware, set the parameters below, and your drone hovers indoors without GPS.

Step 0 — match the protocol to your firmware​

The sensor speaks four protocols; it must be set to the one your firmware expects:

FirmwareSensor protocol
ArduPilotmav_apm
PX4mav_px4
INAVmsp
FMT / custom codeMicolink (protocol reference)

When ordering from our store you pick the firmware variant and it arrives pre-set. To change it later, use MicoAir's MicoAssistant desktop tool (the MTF-02P can also be hard-set via solder pads).

The #1 support ticket

"Distance shows up but no optical flow data" is almost always a protocol mismatch — an mav_px4 sensor on an ArduPilot board, or vice versa. Check Step 0 before anything else.

ArduPilot (≥ 4.2.0)​

Serial and sensor parameters — n is the UART you wired (e.g. SERIAL5):

SERIALn_PROTOCOL = 1      # MAVLink1
SERIALn_BAUD     = 115
SERIALn_OPTIONS  = 1024   # Don't forward
FLOW_TYPE        = 5      # MAVLink optical flow
RNGFND1_TYPE     = 10     # MAVLink rangefinder

Reboot (or refresh parameters), then:

RNGFND1_MIN_CM   = 1
RNGFND1_ORIENT   = 25     # facing down
RNGFND1_MAX_CM   = 800    # MTF-01 — use your sensor's real range:
                          # 1200 (MTF-01P) / 600 (MTF-02P) / 250 (MTF-02)

EKF source — flow-only indoor flight​

This is the part most guides skip. Telling the EKF to trust flow velocity instead of GPS:

AHRS_EKF_TYPE    = 3
EK3_SRC_OPTIONS  = 0
EK3_SRC1_POSXY   = 0      # no absolute XY position source
EK3_SRC1_POSZ    = 2      # height from rangefinder
EK3_SRC1_VELXY   = 5      # XY velocity from optical flow
EK3_SRC1_VELZ    = 0
EK3_SRC1_YAW     = 1      # compass

EKF source — GPS outdoors, flow indoors (advanced)​

Keep GPS as source 1 and configure flow as source 2, switched from the radio. Not recommended as a first setup:

EK3_SRC2_POSXY   = 0
EK3_SRC2_POSZ    = 2
EK3_SRC2_VELXY   = 5
EK3_SRC2_VELZ    = 0
EK3_SRC2_YAW     = 1
RC6_OPTION       = 90     # RC6 3-position switch selects EKF source;
                          # middle position = source 2 (optical flow)
Can't find FLOW_TYPE?

First confirm firmware ≥ 4.2.0. If the version is fine, your board's firmware was built without optical flow support — common on F405-class boards where flash constraints force feature cuts. Use ArduPilot's custom firmware builder to build with flow enabled, or use a board with more flash such as the H743 V2.

PX4​

Sensor protocol: mav_px4. Parameters differ by firmware line:

1.12.x – 1.13.x

MAV_1_CONFIG   = TELEM n     # reboot after setting
MAV_1_MODE     = Normal
SER_TELn_BAUD  = 115200 8N1
SENS_FLOW_ROT  = No rotation
EKF2_AID_MASK  = use optical flow
EKF2_RNG_AID   = Range aid enable
EKF2_HGT_MODE  = Range sensor

1.14.x – 1.16.x

MAV_1_CONFIG   = TELEM n     # reboot after setting
MAV_1_MODE     = Normal
SER_TELn_BAUD  = 115200 8N1
EKF2_OF_CTRL   = Enabled
EKF2_RNG_CTRL  = Enabled
EKF2_HGT_REF   = Range sensor

Reboot again; SENS_FLOW_ROT only appears in QGC after the flow sensor has been detected once (its default "No rotation" is already correct).

1.17.x and later — additionally set MAV_PROTO_VER = 1.

INAV​

Sensor protocol: msp. Enable the optical flow and rangefinder sensors in the INAV configurator. Avoid INAV 7.1.1 — a known bug breaks this sensor family; use a newer (or older) release.

Verify before you fly​

Connect over USB (not telemetry — see below) and open QGC's MAVLink Inspector (or Mission Planner's equivalent). You should see both DISTANCE_SENSOR and OPTICAL_FLOW_RAD messages arriving:

QGC MAVLink Inspector showing DISTANCE_SENSOR and OPTICAL_FLOW_RAD messages

Message rates shown in the GCS are set by the flight controller's link bandwidth, not by the sensor — don't expect to see 100 Hz there, and don't worry about it.

Troubleshooting​

Distance data but no optical flow​

Two usual causes: a protocol mismatch (see Step 0), or you're connected via a telemetry radio — on a slow link PX4 selectively drops messages, so OPTICAL_FLOW_RAD may simply not be forwarded to the GCS. Check over USB before suspecting the sensor.

PX4 keeps resetting my position estimate to zero​

Normal. Optical flow provides velocity only, no absolute position, so while disarmed PX4 periodically re-zeros the estimated position to bound drift.

Position hold is mushy or drifts​

Check the basics the physics demands: ground texture (bare uniform floors are hard to track), light (>60 lux), altitude within the rangefinder's real range, and the sensor lens clean and unobstructed. A printed case keeps fingers and crashes off the optics.

Written and maintained by the Robofusion engineering team. Parameters cross-checked against MicoAir's Chinese manuals (June 2026) and ArduPilot/PX4 documentation.