Gears
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:
a. Calculation of the gear ratio (speed ratio)
b. The photo of the actual gear layout.
c. Calculation of the number of revolutions required to rotate the crank handle.
d. The video of the turning of the gears to lift the water bottle.
5. My Learning reflection on the gears activities.
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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: is the size of the gear teeth. It can be denoted by the letter "m". The larger the value of m, the bigger the size of the gear teeth (in millimeters, mm). Gears that mesh together have the same module.
Pitch Circular Diameter, PCD (in millimeters, mm): the imaginary circle that passes through the contact point of 2 meshing gears. It represents the diameter of 2 friction rollers in contact and moves at the same velocity.
Number of teeth, z: number of teethes. 🦷
the relationship between gear module, PCD and number of teeth can be represented by this equation:
2. Below is the relationship between gear ratio (speed ratio) and output speed for a pair of gears.
Gear ratio = no. teethes of driven gear/ no. teethes of driving gear
The larger the gear ratio, the lower the output speed for the pair of gears.
When the gear ratio is >1, output gear speed decreases
When the gear ratio is <1, output gear speed increases
Below is the relationship between gear ratio and torque for a pair of gears.
When gear ratio is >1, the gear become a torque multiplier and the torque of the driven gear increases.
When gear ratio is <1, the torque of the driven gear decreases.
3. Below are the proposed design to make the hand-squeezed fan better:
After assembling the fan, there was very little wind coming out of the fan. This means that the fan is spinning too slowly.
In order to make the hand-squeezed fan better, we will need to lower the gear ratio. The lower the gear ratio, the faster the output speed of the fan, and more wind will be produced. To do so, the driver gear used should be bigger than the driven gear.
4. Below are the description on how my practical team arranged the gears provided in the practical to raise the water bottle
a. of the gear ratio (speed ratio).
Gear ratio = 40/30 x 40/12 = 4.44
b. The photo of the actual gear layout.
c. Calculation of the number of revolutions required to rotate the crank handle.
Mass of water = 600g = 0.6kg
Weight of water = 0.6kg x 9.81N/kg = 5.886N
Diameter of winch = 6.3cm
Radius of winch = 3.15cm = 0.0315m
Torque = 5.886N x 0.0315m = 0.18541 Nm
Distance moved with 1 revolution = (2 π)(0.0315)= 0.19792m
Distance travelled by bottle = 200mm = 0.2m
Number of revolutions required = 0.2/0.19792 = 1.0105 revolutions
d. The video of the turning of the gears to lift the water bottle.
This practical was fun and I got the chance to experience how gears work. I have never did anything related to gears before, and that was actually my first time working with gears. I am grateful for this opportunity. I got to learn how the different arrangement of gears can lead to different outcomes. For example, based on the second activity we did during the practical session, arranging the gears in another way can make our hand-squeezed fan work more effectively (the blades will spin faster and more wind will be produced --> better results and different outcome).
Another thing that happened during the practical session which I think is worth mentioning was that we did not read the practical manual properly and we did not realize the longest screw provided to us was only 2cm long! We thought we were being smart by stacking our gears together to reach the gear ratio of 27 😭😭. We even went around the class flexing that we got 27 as our gear ratio. In the end, we had to unscrew everything and come up with another gear arrangement. The final gear ratio was definitely lower than our previous attempt, but we tried our best and we also learned the importance of reading the manual thoroughly before carrying out the activity.
We were also tasked to assemble a hand-squeezed fan. But we did not realize that one of the components was broken before constructing the fan. As a result, the fan could not work properly. And again, we had to unscrew everything and continue with a different set.
In conclusion, I found this practical engaging and I think that knowing and understanding the working principles of how gears work is a basic knowledge every engineer should have.
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