Reapeating crossbow was designed by Yuxuan Zhu and me in 2019. We did mechanical design work together. Each of us was responsible for different parts of the mechanism.
The Zhuge repeating crossbow( 诸葛连弩 in Chinese ) is a Chinese crossbow that was invented by Zhuge Liang, one of the most outstanding strategist in Chinese history, during the Warrior State Period about 2000 years ago.
By reading relative literature and restoration drawing sheets, I, along with my teammate Young Zhu, managed to figure out its working principle. We did relative computing to design the mechanical structure of different parts. In order to manufacture a repeating crossbow which worked well, the manufacturing process of milling machines and the assembling process were also carefully designed.
The final model was a 25-inch-long one made of aluminum alloy which was able to shot up to 10 arrows in a row without stretching bowstring by hand.
Origin of Inspiration
Ancient people, with their astonishing wisdom, had already designed all kinds of tools and weapons with ingenious mechanic structure long before the establishment of Newtonian Mechanics.
According to the History of the Wu-Yue War, written in the Eastern Han Dynasty, the repeating crossbow was invented during the Warring States Period. The Ming repeating crossbow improved previous design and used an arming mechanism which required its user to push a rear lever upwards and downwards back and forth.
Much relative research had been done by historians. So we decided to make it come back to live again.
Creative Design and Restoration of Principles
The abstract mechanic structure of a repeating crossbow is a kinematic chain consisting of a three-bar linkage and a slider on a plain with a single degree of freedom.
There is a groove at the end of the sliding rail to fix the taut bowstring. Each time the user push the handler forward, the arrow magazine would move downward correspondingly. A metal cylinder would at the same time push the bowstring out of the groove. The bowstring them trigger the arrow.
The arrow magazine is also specially designed. Gravity makes another arrow fall on the sliding rail to make preparations for the next shot.
Design for Manufacturing and Assembling
We used AutoCAD and Solidworks to finish all the drawing of parts and assembly. All the fits and dimentional tolerance were considered. To minimize the cost of manufacturing, we discussed with Prof. Wu Dan to revise the drawings to reduce work surfaces and optimize the assemble chain.
We chose aluminum alloy as the main manufacturing material to reduce weight of the crossbow. Wear-resisting carbon steel were used on moving surfaces.
A crossbow with metallic luster and one with white and black spray paints on its surface were finally manufactured for different user preference.
We did a simple experiment as the short video shown below. The repeating crossbow worked perfectly.
The project suggested us that attention should be paid to both user experience and manufacturing process during a designer’s creation process.