Mechanisms (Beta) : How they work and how they are used.
Bell Crank
Using Flash
Using Flash
The bell crank is used to convert the direction of reciprocating movement. By varying the angle of the crank piece it can be used to change the angle of movement from
1˚ to 180˚. The change of angle is defined by the angle of the crank, in the top animation the...
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Bridge Structure
We went walking near Keswick this morning. On the return leg of the journey we came across this rather attractive railway bridge, now converted to a foot bridge. It was the structure that caught my eye.
To span a gap this wide the bridge needs to be more that a simple flat beam, an arched...
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Cam follower
The heart of many automata, both traditional and the paper variety, is the cam. The cam is perhaps the most flexible way of driving a mechanism. By changing the shape of the cam profile all sorts of different movements can be described.
But on its own, a cam just goes round and round. To use...
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Cams
Cams are a simple mechanism that can be used to create quite complex movements. As the cam turns a cam follower, which is touching the surface of the cam, moves up and down in a movement described by the profile of the cam.
In a simple cam such as the egg shaped cam shown here, the cam...
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Chain and Sprocket
Like gears, chain and sprocket drives are used to transmit rotary motion from one place to another and just like gears the ratio of speed between two sprockest is the same a the ratio of the number of teeth. In the example below there are two wheels, one with twelve teeth one with twenty. 12:20 is...
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Gear Train
In a clock the minute hand runs at one sixtieth the speed of the second hand. The clockmaker could
connect the two with a 60:1 gear but even with a small 10 tooth drive wheel she would still need a 600 tooth main wheel!
To make the mechanism more compact horologists (clock and watch makers)...
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Gears
Gears are used to change speed in rotational movement and to move rotation from one place to another. In the example below the brown gear has twenty teeth and the light brown gear has eight teeth and the grey gear has twelve teeth. As the brown gear turns one turn the light brown gear turns 20/8 or...
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Geneva Drive
The Geneva drive is named after the city of its invention where it was used in the construction of clocks.
Originally the Geneva mechanism was used as a way of preventing springs from being wound too tight. One of the slots would be blanked off so the winder could only be turned a fixed number of...
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Involute Gears
As promised in yesterday's blog, a post about the construction of involute gears. The profile of the side of an involute gear is defined mathematically but you can also construct it with a few household items. Simply put, it is the curve you get as you unwrap a string from around a cylinder....
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Levers
Levers come in three types, or 'orders' The different orders refer to the way the three main parts of the lever are laid out. That is, the fulcum or pivot point, the load, the thing to be moved and the force. In a first order lever, the fulcrum is in the middle between the force and the load, like...
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Peaucellier Linkage
Invented in 1864 the Peaucellier linkage (poo-selli-yeah) linkage was created as a way of making straight line from circular motion. It was used in steam engines to control valves without the need to guides. The peaucellier linkages, invented by, you guessed it, monsieur Peaucellier, is mathematics...
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Piston
The piston mechanism is used to convert between rotary motion and reciprocating motion, it works either way. Driving the wheel will move the piston back and forth, in this form the piston can be used to pump liquids for example creating the high pressure need in a good coffee machine....
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Rack and Pinion
The rack and pinion is used to convert between rotary and linear motion. The rack is the flat, toothed part, the pinion is the gear. Rack and pinion can convert from rotary to linear of from linear to rotary.
The diameter of the gear determines the speed that the rack moves as the pinion...
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Rack and Pinion - Modified
More Flip Face Fun: Animation test for mechanism #4.
I've jumped past the original Rack and Pinion idea straight to this. The lower gear is a six tooth section from a forty tooth gear. The pivot point at the bottom is where the centre of the gear wheel would be. The top gear is an eight tooth gear...
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Ratchet - Five Tooth
A five toothed ratchet mechanism soon to be implemented in card.
As the housing moves back and forth the pawl drops into the tooth and advances the gear one fifth of a turn before returning to engage the next tooth.
The second pawl, at the bottom of the picture, stops the gear from rotating back as...
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Ratchet - Two Teeth
This animation demonstrates the movement of the two-toothed ratchet mechanism. The housing rocks back and forth, at the bottom of its throw the pawl clicks down and catches on the next ratchet tooth. As the housing moves back it pulls the ratchet gear with it. At the bottom of the mechanism is a...
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Ratchet Mechanism
I came across this alternative way of using a ratchet as a drive mechanism. The lever on the right is the input. Pull it back and forth to intermittently drive the wheel forward. As the lever is pushed anti-clockwise it lifts the pawl out of the gear before turning it back leaving the gear...
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Rotary Motion
Rotary motion is motion in a circle. As a mechanism rotates it turns about a fixed point. The speed of rotation is measured in revolutions per minute or rpm. This the number of complete rotations made in one minute.
Using Flash
It is the starting point for many mechanisms. Measurement: Rotary...
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Watt Linkage
The original steam engines used pistons that were powered in only one direction. As the piston pulled down, it pulled on a chain link over a curved rocker similar to the nodding donkeys seen in oil fields. When James Watt realised that he could dramatically increase the power and efficiency of the...
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