precise landing by openmv | ardupilot preland init fail

katie · January 26, 2024, 1:04pm

Hi guys! I am trying to use openmv as the camera for the precise landing mode of ardurpilot.
I use the official example code mavlink_apriltags_landing_target_1.py. The camera and QR code have been tested and can transmit information at a distance of about 3m. The corresponding information and parameters can also be seen on QGroundControl. but when I take off and land by QGroundControl, it often displays “land target found”, and then displays “preland init fail”.
Is my code or setting wrong? I have a flight log file. Can anyone help me? I would appreciate it really much.

ppoirier · January 26, 2024, 1:18pm

Hello,

Referring to the code == we have lost the target, not enough readings to initialize the EKF

github.com

ArduPilot/ardupilot/blob/master/libraries/AC_PrecLand/AC_PrecLand.cpp#L605


      
          
          
          // check if EKF got the time to initialize when the landing target was first detected
          // Expects sensor to update within EKF_INIT_SENSOR_MIN_UPDATE_MS milliseconds till EKF_INIT_TIME_MS milliseconds have passed
          // after this period landing target estimates can be used by vehicle
          void AC_PrecLand::check_ekf_init_timeout()
          {
              if (!target_acquired() && _estimator_initialized) {
                  // we have just got the target in sight
                  if (AP_HAL::millis()-_last_update_ms > EKF_INIT_SENSOR_MIN_UPDATE_MS) {
                      // we have lost the target, not enough readings to initialize the EKF
                      _estimator_initialized = false;
                      gcs().send_text(MAV_SEVERITY_CRITICAL, "PrecLand: Init Failed");
                  } else if (AP_HAL::millis()-_estimator_init_ms > EKF_INIT_TIME_MS) {
                      // the target has been visible for a while, EKF should now have initialized to a good value
                      _target_acquired = true;
                      gcs().send_text(MAV_SEVERITY_INFO, "PrecLand: Init Complete");
                  }
              }
          }

katie · January 26, 2024, 1:28pm

Hello, thank you very much for your reply!
Yes I have read the code, but the instructions are a bit vague, does this situation require me to resize the Apriltag? I printed an Apriltag of approximately 50cm*50cm, or should I adjust the position where OpenMV is placed?

ppoirier · January 26, 2024, 1:33pm

Look at mavlink inspector on QGC - my guess is that you are missing readouts due to vibration

Make sure the vibration level is minimal and camera is fixed with vibration pads or else

katie · January 26, 2024, 1:55pm

thank you very much for replying again!
This is my log. Does it refer to this vibration parameter?

the parameter is around 1-5/2-8, does it matter a lot?

My openmv is indeed not very stable. It is attached with Velcro.

Thank you very much for your help! I’m trying to find a solution from this aspect!

katie · May 12, 2024, 4:10am

I’ve tried to used a 3d-printed part for openmv, which can help to connect the openmv to the drone. The connection is quite stable I think. But the problem still existed, so I am here for help again.

The log said that The target was found at first, but got lost again in the next 2 or 3 seconds, and failed to complete the precise landing process.

Ps: the apriltag I printed is 5050cm, and I also tried for 11m, but still doesn’t work.