A classic Newton's Cradle that uses 6 pencils to reduce the amount of plastic required. Print 5 slings, 5 hangers and 4 supports. Use monofilament or string to hang the slings from the top rails. The slings are sized for a 1" ball bearing, adjust as needed for what size you use. I highly recommend printing a set of Hangers first to confirm they will fit your pencils, evidently pencil sizes vary greatly so you want to have a tight fit on the ones you have.
When assembling make sure the erasers are on the bottom of the assembly, this will keep it from moving when it is in action. You can use tape or glue to hold the top braces and hangers in place. I recommend glueing the ball bearings in the slings, the shock can pop them out if they are not tight.
Adjust sizes of STL files to fit your materials!