How large are the black wheels?
The wheels are small.
    src        edge_attr  dst
0     0   to the left of    7
1     0   to the left of   11
2     3   to the left of   11
3     3   to the left of    7
4     3   to the left of    5
5     4  to the right of   10
6     5  to the right of    3
7     5   to the left of    8
8     7  to the right of    3
9     7  to the right of    0
10    7   to the left of   10
11    8  to the right of    5
12   10  to the right of   11
13   10  to the right of    7
14   10   to the left of    4
15   11   to the left of   10
16   11  to the right of    0
17   11  to the right of    3