Gears

 Gears Documentation Blog Entry


In this page, I will describe:

  1. The definition of gear module, pitch circular diameter and the relationship between gear module, pitch circular diameter and number of teeth.

  2. The relationship between gear ratio (speed ratio) and output speed, between gear ratio and torque for a pair of gears.

  3. How I can design a better hand-squeezed fan, including the sketches

  4. How my practical team arranged the gears provided in the practical to raise the water bottle, consisting of:

  1. Calculation of the gear ratio (speed ratio) 

  2. The photo of the actual gear layout.

  3. Calculation of the number of revolutions required to rotate the crank handle.

  4. The video of the turning of the gears to lift the water bottle.

  1. My Learning reflection on the gears activities.



  1. These are the definition of gear module, pitch circular diameter and the relationship between gear module, pitch circular diameter and number of teeth:

Gear module (m) refers to the size of the teeth. The larger the gear module, the larger the teeth of the gears. Gears that mesh together have the same module.

Pitch circular diameter (PCD) is the imaginary circle that passes through the contact point between two meshing gears. It represents the diameters of two friction rollers in contact and moves at the same linear velocity.


The relationship between the gear module, pitch circular diameter and number of teeth can be represented by

where z represents the number of teeth


  1. Below is the relationship between gear ratio (speed ratio) and output speed for a pair of gears.

Gear ratio is the ratio of the number of teeth of the follower gear to the number of teeth of the driver gear.

The smaller the gear ratio, the higher the output speed for a pair of gears. 

When the gear ratio is low, there is an increase in speed.

When gear ratio <1, it becomes a speed multiplier and the output of speed of the follower gear increases. 

When gear ratio >1, the output speed of the follower gear decreases. 


Below is the relationship between gear ratio and torque for a pair of gears.

The larger the gear ratio, the higher the torque for a pair of gears. 

When the gear ratio is high, there is an increase in force ratio.

When gear ratio >1, it becomes a torque multiplier and the torque of the follower gear increases. 

When gear ratio <1, the torque of the follower gear decreases. 


  1. Below are the proposed design to make the hand-squeezed fan better:


To make the hand-squeezed fan, we arranged the gear such that the gear ratio is small as the smaller the gear ratio, the higher the output speed of the gears. Hence, wind will be blown faster.


To make the hand-squeezed fan better, the compound gear can have lesser teeth on the smaller gear. This will hence decrease the gear ratio at each line of action. Therefore, the overall gear ratio will decrease and the output speed of the gears will increase.



  1. Below are the description on how my practical team arranged the gears provided in the practical to raise the water bottle. 

  1. Calculation of the gear ratio (speed ratio).


  1. The photo of the actual gear layout.


  1. Calculation of the number of revolutions required to rotate the crank handle.


  1. The video of the turning of the gears to lift the water bottle.


Unfortunately, we were not able to lift the water bottle up by 200mm. The gears got jammed after around 10 revolutions due to the glue used to stick the string to the winch.



  1. Below is my Learning Reflection on the gears activities

The practical overall was very fun. I get to learn how the gears⚙ actually work and the importance of the arrangement of the gears. The arrangement of the gears can affect the gear ratio, which will affect the output speed and torque of the follower gear. Even though I have used gears as a mechanism for ICPD, I did not know how to effectively make use of it. Learning about gears will be beneficial for us as it is used commonly in products. Learning to effectively use it allows us to design a product that can be improved through the use of gears.

I enjoyed activity 1 as we got to try out and test different arrangements of gears to achieve the highest gear ratio. Instead of telling us what is the highest achievable gear ratio, we get to investigate 🔎and try and rearrange to achieve the highest gear ratio. Initially, the gear ratio we got was 2.96. We got it by lining up the gears in a small to big manner. However, we saw another group stacked the gears. Hence, we also tried stacking the gears and managed to obtain a gear ratio of 26.7. This experience made me realise that we shouldn’t think that there is only one way to do things. We should start thinking from another perspective. There wasn’t any rule that states that we cannot stack it up but my first instinct was to just line them up and try to achieve the highest gear ratio. I learnt that I shouldn’t set up limitations/ restrictions for myself and should push myself and start thinking from another perspective.

Activity 2 was very rushed as we took too much time doing activity 1. In the end, we had to split the work with 1 pair finishing up activity 1 and dismantling and another pair working on activity 2. It was very stressful as we had to complete all the questions by the end of the practical. To improve on these, we should have split the work more clearly. For example, all 4 of us was working on Q1 & 2 and building the gear layout. When it was time to move on, Q3-5 of activity 1 was still incomplete. We could have split the work such that 2 people work on arranging the gears, 1 person to do Q1 & 2 and the other person do Q3. After that the gear layout has been built, 1 pair can then move on to do Q4 & 5 and another pair start on activity 2. Time ⏲ management is very crucial and we should learn to better manage and planned our time to complete the given task within the time frame.