Ball track doesn't work

[hannesa2]

It would be nice, if delivered software would work out of the box

This python3 ball_track/ball_tracker.py runs into

[ WARN:0] global /tmp/pip-wheel-qd18ncao/opencv-python/opencv/modules/videoio/src/cap_v4l.cpp (893) open VIDEOIO(V4L2:/dev/video0): can't open camera by index
DEBUG "back_wheels.py": Set debug off
DEBUG "TB6612.py": Set debug off
DEBUG "TB6612.py": Set debug off
DEBUG "PCA9685.py": Set debug off
DEBUG "front_wheels.py": Set debug off
DEBUG "front_wheels.py": Set wheel debug off
DEBUG "Servo.py": Set debug off
Begin!
Traceback (most recent call last):
  File "ball_track/ball_tracker.py", line 257, in <module>
    main()
  File "ball_track/ball_tracker.py", line 97, in main
    (tmp_x, tmp_y), tmp_r = find_blob()
  File "ball_track/ball_tracker.py", line 202, in find_blob
    bgr_image = cv2.medianBlur(bgr_image, 3)
cv2.error: OpenCV(4.5.1) /tmp/pip-wheel-qd18ncao/opencv-python/opencv/modules/imgproc/src/median_blur.dispatch.cpp:283: error: (-215:Assertion failed) !_src0.empty() in function 'medianBlur'