Today I carried on reading The Pit and The Pendulum, and wrote some more notes to get a better understanding of the story.
What I am really surprised about is that I missed some very important detail in the book, like the dungeon is squared, and the walls are made of metal, while the floors are made of stone.
And I also missed the shape of the pendulum, I thought the end was a circular shape, but it wasn't it was crescent shape.
Here are some more scans of my notes and doodles.
also some reference pictures to give me an idea on making the crescent pendulum.