Levers
A lever is a device that applies or transfers force. It is a simple mechanism that usually consists of a rigid length of wood or metal, which pivots on a fixed point called a fulcrum.Most machines employ some form of lever, and you will find that they are used a lot in automata. It is therefore useful to understand how they work and how to use them in your own designs.
Levers work on the principle of mechanical advantage which can be calculated by a simple equation, and is used to compare the effort applied to the load moved.
Archimedes established the Law of the Levers in his book On the Equilibrium of Planes. He described the three separate types (or orders) of levers, which have their fulcrum, effort and load arranged in different ways.
A first order lever has its fulcrum point between the load and effort.
A second order lever has its fulcrum and effort at opposite ends, and the load somewhere between the two.
The third order lever has the fulcrum and load at opposite ends with the effort somewhere between the two.
A lever can produce a small output motion from a large input force, as when using a crowbar. A lever can also be used the other way round, where a small input movement can be increased by a lever to create a larger output movement such as a pair of scissors.
Moving the fulcrum point, the effort or load points can change the effectiveness of a lever. For example if you move the fulcrum point on a first order lever towards the effort, the load travels further but takes more force to move it. The opposite happens when you move it towards the load.
The important thing about levers is the way that they can be used to transmit, amplify or decrease movement. In engineering terms you are experimenting with the Mechanical Advantage of the lever. When a small effort moves a large load the effort has to move a much greater distance than the load. This is the price to pay for gaining mechanical advantage.
The formula for working out the ratio of a lever can also be used to work out the Amplification or amount of movement a lever will travel. Just like a cam, this is referred to as the Throw and can be used to great advantage when designing.
Mechanical advantage/Effort = Load
The ratio of A to B is 6cm to 2cm, so applying the formula returns a ratio of 3:1. This means for every 3cm of travel at effort (A) the load (B) will move 1cm. Reverse this by moving the fulcrum towards the effort and we magnify the movement for every 1cm of travel on the effort (B), so the load (A) will travel 3cm.
It is also important to remember that levers travel in (describe) an arc and do not move in a straight line.