Leonardo's crossbow

Design

Leonardo's crossbow designs incorporated features that improved upon earlier crossbows. A narrower shaft and tapered bolt adjusted the nocking of arrows, which improved airflow and reduced drag, allowing more efficient operation and more precise aim. These ideas were developed independently. The mathematics Leonardo used in his designs applied geometrical laws of motion to machine design, though some inaccuracies are known by modern standards.

Proportional techniques were employed throughout. The rapid-fire crossbow's tiller was split into two stacked wooden pieces held together at the front by a hinge and at the back by a spring-loaded latch. Inside the tiller, a pair of interconnected folding levers attached the lower half to a sliding plank on the top half between the two metal prods, similar to the Gastraphetes, containing a rolling nut and spring-loaded sear. The bottom half held the trigger.

Pressing a switch released the latch, allowing the bottom half to fold down; the levers pushed the sliding plank forward until the drawstring was caught by the rolling nut, secured by the sear's spring tension. Pushing the bottom half back locked the tiller halves together. After loading a bolt and aiming, pulling the trigger compressed the sear's spring, releasing the drawstring to propel the bolt. This design eliminated the need for external spanning tools.

Working replicas

A working replica of the rapid-fire crossbow was released on 24 June 2015 during a demonstration at the Castello Sforzesco in Milan, following a prototype built in 2013. The study was conducted by Edoardo Zanon of the Leonardo3 study center, using processing and assembly techniques available in Leonardo's time. The model allows precision shooting and has a fast internal spanning mechanism. It is on display at the Leonardo3 – The World of Leonardo museum in Milan. The giant crossbow was never constructed by its designer, but a working model built to a 1:1 scale was shown in the ITN documentary Leonardo's Dream Machines, first aired in February 2003 by Channel 4.