After two and a half years of hardly looking at my Knex, I bring you one of the projects I found stashed away in my closet.
Here is a padlock that uses a simple key to unlatch a ratchet system that hold the shackle in place when locked. I used a small spring to keep tension on the ratchet, but you can use a weak rubber band if a spring is not available. I also used a cut blue rod for the ease of putting it together, but again its not necessary.
I hope you enjoy the build. I'll be posting pictures of the handful of projects I still have put together.