Stone-hurling engine with springing arms
A bending driving-beam makes the whole motion composite and casts the stone farther
A large timber engine for hurling stones is drawn on its rectangular base, its power stored in two great curved arms sprung within the frame and delivered through a long throwing beam that ends in a cup at the left. Leonardo's note reasons that if the beam driving the stone is allowed to bend somewhat, the machine will cast the stone much farther, because the whole motion then becomes composite. It is one of his spring-driven throwing engines.
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Composite motion gives greater range
The accompanying note argues that letting the driving beam bend adds a second component of movement, so the stone leaves the engine with a compound (composite) motion and travels much farther than from a rigid arm.
Frame with paired springing arms and throwing beam
Two great curved arms are sprung within a rectangular timber frame and connected to a long throwing beam. The beam runs diagonally to a cup at the far left where the projectile is held.
Engine for casting stones
The apparatus is built to throw stones: the projectile rides in the cup at the tip of the long arm and is driven off when the sprung arms release.