'Recognizing the need is the primary condition for design.'

Charles Eames

'To design is to communicate clearly by whatever means you can control or master.'
Milton Glaser

Gears and Ratios

Gears are an essential part of most mechanical devices.


Gears fit (mesh) togeather by interlocking teeth.


The size of the diameter of the gear cog is directly related to the number of teeth it has.


Knowing the number of teeth of two meshed gears allows us to be able to work out the power rating of the gear system or gear train.

Driving and Driven Gears: 

There are two names we give gears depending on where they are set in the gear train.


Each gear train has an INPUT gear and an OUTPUT gear.


The INPUT gear is also sometimes known as the DRIVE GEAR


The OUTPUT gear is also sometimes known as the DRIVEN GEAR 

Principals of gear direction:

When two gears are mesheed together the driven gear will always turn in the opposite direction to the drive gear. 


To change the direction again another gear needs to be added to the gear train. 




Task 1: Download the worksheet on gear direction and complete the questions.

Adobe Acrobat document [93.9 KB]

Calculating gear ratios:

To calcualte the ratio of two meshed gears take the number of teeth of the driven gear and divide it by the number of teeth on the driving gear. 


Task 2: Download the worksheet on gear ratio and complete the questions.

Gear ratio worksheet
Gear Ratio Worksheet (1).pdf
Adobe Acrobat document [49.1 KB]

Idler gear:

Idler gears are used when you need to transfer power accross a larger distance or make a change in rotational direction between the input (driving) gear and the output (driven) gear.


Idle gears do not add more power or chage the ratio of the driven to driving gears in any geared system.


They are called idle because they neither add or take away any mechanical advantage. 

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© Julian Kupper