棘輪(ratchet)

棘輪(ratchet)：是一種使得線性往復運動或旋轉運動保持單一方向的機械機構,用以防止傳動機構逆轉

棘輪的運用：

• 絞盤
• 時鐘
• 千斤頂
• 雲霄飛車
• 束線帶
• 驗票閘門
• 手銬
• 棘輪套筒扳手

棘輪構造

1. 齒輪
2. 棘爪
3. 固定用的基底

A ratchet mechanism is based on a wheel that has teeth cut out of it and a pawl that follows as the wheel turns. Studying the diagram you will see that as the ratchet wheel turns and the pawl falls into the 'dip' between the teeth. The ratchet wheel can only turn in one direction - in this case anticlockwise.

起重棘輪·千斤頂

棘輪條B上之齒與槓桿A上的棘爪相契合,另一個棘爪D用來防止棘齒條向下滑落0起重棘輪常用於千斤頂,是汽車換胎的工具。

利用棘輪機構製作橡皮筋手槍

樂高_橡皮筋手槍組裝圖

樂高達芬奇的彈射器Catapult

Model of one of the Leonardo da Vinci’s less famous inventions: a catapult using a leaf spring to fire projectiles, which makes it unique in terms of Medieval technology. The original catapult was to use a single wooden leaf spring – an idea probably inspired by a bow. It did not become popular due to high manufacturing costs at the time. There was a number of full-size models recreated today, and they proved capable of throwing stone projectiles just under a quarter mile. My model, whose scale is difficult to determine, can throw a regular Lego ball just under two meters.

It took me a while to find a Lego element of proper elasticity – I eventually settled for two 12 L axles. It seemed that the axles will get bent permanently from the tensions present in the model, but eventually the did not – they turned out to be perfectly straight after disassembly. I believe a catapult using the same principles to work without risking damage to any Lego pieces could be made with two rigid levers mounted on tension bars, but that would look very much different from Leonardo’s original design. I wanted the model to be mechanically accurate; this is also why I didn’t include any arm-stopping mechanism that could potentially increase the range – I simply haven’t found any in the original drawings.