'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


There are two main transmission (drive gearing) systems that are in common use today:


1: Manual transmissions (Sliding mesh)

2: Automatic transmissions (Planetary gear)


The main differences between the two systems is that in the manual system the driver uses a gear selection shaft to manually move the main shaft into different positions to change the gear ratios between the input and output shaft. 


In an automatic gear system a Planetary gear system is used which is connected to various sensors that detect and respond to different parameters:

  • Vehicle speed sensor (VSS) 
  • Wheel speed sensor (WSS) 
  • Throttle position sensor (TPS)


Sliding Mesh Gearbox:

In a sliding mesh gearbox the input and output (drive and driven) gears are connected using a range of different cog / gear sizes that can slide along the middle shaft.


The input and output shaft rotate on thier axis but the cogs on them stay in position while the gear selector shaft is slid to different points which connets different gears e.g. 1st, 2nd, 3rd etc. 


As with other idler gears you can calculate the ratio by simple counting the number of teeth on the output gear and dividing it by the number of teeth on the input gear and ignore any idler gears in terms of calculation. 




Below there are three pictures of a simple lego 3 speed gearbox.

Image 1: The gear box is set to 1:1 ratio 

Image 2: The gear box is set to a neutral (non meshed) setting

Image 3: The gear box is set to a 3:1 ratio  


(Notice that the cog positions and the position of the gear selector stick are different depending on the setting of the gear box) 


Task 3: Download the worksheet and complete the following:


Easy: Label the parts of the diagram

Medium: Draw your own diagram and label it

Hard: Draw your own diagram, label it and write a short explanation of how the system works

Sliding mesh gearbox
Sliding mesh gearbox worksheet
Sliding mesh gearbox worksheet.jpg
JPG image [123.6 KB]

Planetry gears:

Planetary gears general rules:


  • The ring gear is useually fixed while the sun gear is usually being driven


  • Each set of planetary gears useually has three possible ratios


  • To add more gears another planetary gear ring is added to the first and can be selected when needing gears above or below the first set of three


Task 4:

Watch the video below and note down anything you are still unclear about 


Discuss anything you have identified with your collegues and / or your tutor until you understand and can explain in your own words how a planetary gear system works. 

Task 5:

Download the worksheet and label the parts of a planetry (elipitical) gear system. 

Planetary gear worksheet
Planetry gear worksheet.jpg
JPG image [72.4 KB]
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© Julian Kupper