Hello everyone, In this page, I will describe:
The definition of gear module, pitch circular diameter and the relationship between gear module, pitch circular diameter and number of teeth.
The relationship between gear ratio (speed ratio) and output speed, between gear ratio and torque for a pair of gears.
How I can design a better hand-squeezed fan, including the sketches
How my practical team arranged the gears provided in the practical to raise the water bottle, consisting of:
Calculation of the gear ratio (speed ratio)
The photo of the actual gear layout.
Calculation of the number of revolutions required to rotate the crank handle.
The video of the turning of the gears to lift the water bottle.
My Learning reflection on the gears activities.
To start off, here is my CPDD practical group! I will be stuck with them for every subsequent practical.
So what are gears?
They are basically wheels with teeth that works with other gears to transfer rotation and forces.
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 refers to the size of the gear teeth.
The unit is mm.
The larger a module number, the larger is the size of the teeth.
Gears that mesh together have the same module.
Pitch Circular Diameter 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.
Gear module = pitch circular diameter / number of teeth
Below is the relationship between gear ratio (speed ratio) and output speed for a pair of gears.
Gear Ratio = input speed / output speed
Speed Ratio = output speed/ input speed
Below is the relationship between gear ratio and torque for a pair of gears.
When gear ratio increase, torque increases.
Activity 1: Lifting water using gears
Below are the description on how my practical team arranged the gears provided in the practical to raise the water bottle.
Calculation of the gear ratio (speed ratio):
40/30 40/20 20/40 30/40 30/30 40/30 40/40
Gear ratio = 40/30 x 40/20 x 20/40 x 30/40 x 30/30 x 40/30 x 40/40
= 4/3
= 1.33333333
The photo of the actual gear layout:
Calculation of the number of revolutions required to rotate the crank handle.
Diameter of the winch = 22 mm
Distance travelled by the output gear = Distance travelled by the water = 20cm =200mm
RPM2 = 200/22π = 2.89 rotations
Gear ratio = RPM1/RPM2
4/3 = RPM1/2.89 rotations
RPM1 = 4/3 x 2.89 rotations
= 3.853 rotations
Video of the turning of the gears to lift the water bottle:
From our video, the number of revolutions in the output wheel was approximately 3
Activity 2: hand powered fan
Video of the fan in action:
Below are the proposed design to make the hand-squeezed fan better:
1. the output gear can be smaller, and the input gear can be larger
this is so that one squeeze of the handle can have more rotations of the fan.
Calculations
original:
gear ratio = 10/20 x 9/20 x 9/20
= 0.101
speed ratio = 1/0.101
= 10.1
1 rotation of the output gear = 10.1 rotations of input gear
new:
gear ratio = 10/30 x 9/20 x 5/20
= 0.0375
speed ratio = 1/0.0375
= 26.66
1 rotation of the output gear = 26.66 rotations of input gear
2. A spring can be attached between the handle and the body of the fan
this is so that users need not pull the handle out after squeezing it to complete 1 rotation
My Learning Reflection on the gears activities:
Before this practical, I already sort of knew how gears work as they are everywhere in our daily lives. It was pretty obvious that a smaller gear would turn faster than a larger gear. However, what I did not know was that a smaller gear would have a lower torque as compared to a larger gear.
In the practical, I just did some of the questions that were unmarked in the first half. I then passed the remaining questions to Gayathri to complete and went to assemble the hand-squeezed fan with Redza. While all of this was happening, Enzo and Ryan did activity 1. We did this so as to save time so that we have enough time for the quiz at the end.
I felt that I should have read the instructions for both activities despite not participating in activity 1. We should have done calculations first in order to determine the best gear configuration. Enzo and Ryan set up the gears on the board right away when we could begin our experiment. Our group had a gear ratio of 1.333 which is okay as it is more than 1 but another group managed to get 26. This had taught me that planning ahead is more important than completing the experiment quickly.
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