Cleon
Legend
The other invention they explored was a giant crossbow designed to hurl stones. They built and rebuilt this one, and near the end of the show they fired it.
The machine was huge, by the way, and the stone they threw was about the size of a grapefruit. Maybe a small melon. It went about 60 feet total, and while they called it a success, I saw it as a dismal failure.
I remember that show or one much like it.
The design was so obviously doomed that one wonders whether Leonardo did it deliberately - I do recall reading stories that he didn't like to invent weapons and sabotaged some of his designs.
It's pretty much impossible to build a large tension-powered missile thrower - the mechanical strain of bending the bow to store energy will cause it to snap.
There's a reason why siege engines have been torsion-powered or counterweight-powered for since the ancient Greeks. Using an elastic block or weight to store the energy means your throwing arm(s) can be thick enough not to bend and break when the machine performs its intended task.
There is a trick to somewhat exceed the limits of a bow-powered missile thrower - the Multiple Bed Crossbow. Instead of one bow at the limits of the materials available, you have two or three bows with the bowstrings linked to combine their energy:

I doubt they were any better than a similarly-sized torsion arrow shooter such as a cheiroballista though.