I demonstrated the main concepts for this project. See top left picture.
Horizontal to vertical connections use 2 black connectors in two beams
with 2 plates between.
To connect beams to beams for the base use a plate below and above.
I asked one student to tell what I had explained and he said "sturdiness".
So this time I am saying the project is about sturdiness instead of
stability.
Certainly both are need for a swing set.