Blog 1: Gears ⚙
Hello everyone! Welcome to my first blog on my journey on CPDD. Today, I will be sharing with you guys on what I have done for my practical 1. Basically, I felt that I was in a mechanical engineering student when I did this. Without further ado, let me share with you what I have done.
Part 1: Definition and relationship of gear module (m), pitch circular diameter (PCD) and the number of teeth (z)
Before I tell u the definition and relationship of it, it is important to understand how it looks
like.
Figure 1: Representing the different definition of a gear
Pitch Circular diameter (PCD) as seen from figure 1, it means that there is an imaginary circle around the contact between two meshing gears.
Gear module (m) is the size of the gear teeth and the unit is is mm.
Number of teeth (z) is simply the count of the number of the individual teeth around the gear's circumference.
Figure 2: Relationship of m, PCD, and z
Now, moving on to the relationship, they are link by a relationship shown in figure 2. Basically, what this equation means is that it is determining the number of teeth of that we can fit inside a gear with the same gear module.
Furthermore, as you can see from the above relationship, you will realise that Pitch Circular diameter is directly proportional to Gear module but the number of teeth is inversely proportional to gear module.
Part 2: Relationship between gear ratio, output speed and torque for a pair of gears
For starters, gear ratio or speed ratio is the relationship of the number of teeth of the output gear over the number of teeth of the input gear. The formula is as shown below where z2 is the number of teeth of the follower gear and z1 is the number of teeth of the driver gear.
Figure 3: Formula of gear ratio and z
Therefore, the relationship between output speed, gear ratio and torque for a pair of gears can be represented by the following relationship.
Figure 4: Relationship of RPM, gear ratio and T (subscript 2 is the follower gear and subscript 1 is the driver gear)
Before I explain the relationship above, it is important to know what does torque (T) and Revolutions Per Minute (RPM) mean. T refers to the measure of rotational force applied to the gear. While RPM refers to the number of complete rotations the gear makes which usually refers to the speed of the gear.
With that in mind, by looking at the figure 4, we can tell that RPM is inversely proportional to gear ratio. Hence, when gear ratio increases, the driver gear's RPM will increase. T is directly proportional to gear ratio. Therefore, when gear ratio increases, follower gear's torque increase too.
Additionally, we can also draw a relationship between PCD, z and gear ratio. This can be seen from the equation below.
Figure 5: Relationship showing relationship between PCD, z and gear ratio
The relationship shown in figure 5 is true when 2 gears are meshed together, the gear modules of the 2 gears must be the same in order to turn smoothly. Hence, m1 must be equal to m2, we can also conclude that PCD is directly proportional to gear ratio, and when gear ratio increases, the PCD of the driven gear is bigger.
Figure 6: Relationships of between gear ratios, PCD, z, T, RPM
In a nutshell, when we put all relationships together, when the gear ratio is higher, the number of teeth of the follower gear will increase, the follower gear's PCD will be smaller, causing torque to increase which causes a lower input force but speed to decrease.
Part 3: Proposed design of a better hand-squeezed fan
For practical 1, I realise that there was some issues I have when I assembled the hand-squeeze fan.
It was difficult to crank the handle causing it to make the fan turn
It requires a large amount of force for it
The fan speed was not sufficient
Hence, with these issues that I have faced, I have came up with interesting solutions for it!
Solution for problem 1:
First and foremost, to tackle the difficulty of cranking the handle, we can possibly add a spring mechanism that can push the handle back easily when a crank is done. This is how it looks like.
Figure 7: Online reference of an improved design Credits:하비연 Hobbyeon [Craft] (2021). Making a hand fan without motor and battery. [online] YouTube. Available at: https://www.youtube.com/watch?v=sflxH8zXA4Y [Accessed 15 Nov. 2024].
Figure 8: My crank mechanism of the current hand squeeze fan
Instead of an actual spring, we can use a rubber band to make the handle return to its original spot so that we can crank the handle more easily. As seen from figure 8, the handle is directly connected to the gear, this causes the handle to harder to crank as the user cannot crank the handle whenever they wish to. However with the addition of the rubber band, it will pull back the handle when it is being stretched as seen from figure 7. This allows the user to crank again easily, without pulling the handle back manually.
Solution for problem 2:
Secondly, to tackle the problem of putting a large amount of force to the handle, the solution I propose is to have a compound gear at the handle. This will reduce the amount of input force needed when the handle is cranked. In addition, there will also be no change in the gear ratio. Furthermore, the handle has also its own independent teeth which can catch the teeth of the gear perfectly. This way, it reduces the need of waiting for the gear to fully rotate before the user crank again.
Figure 9: Drawing of the proposed hand-squeezed fan
Solution for problem 3
Last but not least, the final solution I have is to have a mechanism that pushes away the gear that is connected to the fan blade. Figure 10 and 11 will represent what I meant.
Figure 10: Visual representation on how the gears move
Figure 11: Blue circle showing how the gear moves from the outside Credit:하비연 Hobbyeon [Craft] (2021). Making a hand fan without motor and battery. [online] YouTube. Available at: https://www.youtube.com/watch?v=sflxH8zXA4Y [Accessed 15 Nov. 2024].
From the figures 10, it shows that how the gears move away from the last gear which allows the final gear to produce momentum to the fan allowing it to spin faster. While in figure 11, it shows that there is a gap on the cover of the fan, which allows the compound gear to slide down. Additionally, the other compound gear that is connected to the handle has no gap to slide down. Hence, if the handle is released, the gears will returned back to its original position, and more momentum can be added to the fan when needed. This will then have more wind!!!
Part 4: Water Bottle Challenge
This challenge was not easy to be honest as we had a long time to figure out the gear ratio first and then followed by the gear layout. Nonetheless, with determination we managed to solved it!!!
Calculation of the gear ratio
Photo of the actual gear layout
Calculation of number of revolutions required to rotate the crank handle
Video of my group lifting the water bottle by turning the gears
Part 5: My learning reflection on gears activities
I believe that this practical was an eye opening and fruitful experience for me as I got to understand how gears work in reality, and the various theories of gears such as calculating gear ratio, torque and RPM. On the theory aspect, my peers and lecturers made me appreciate the meaning of gears better by explaining their thoughts. This made me have a better understanding about gears as I thought that gears were just a set of wheels with teeth that just move with each other. For instance, my peers had some prior knowledge about gears before and told my team the rough estimate on the desired amount of gear ratio. My lecturers also thought us the different relationships with gear ratio, which allow me to calculate gear ratio easily. Therefore, with that in mind I have now more perspective on how gears work such as the direction it rotates and the theory side of it.
This practical has also made me realise that I must not rely on estimations, but rather using logic to solve the problem which can save my group time. For example, when my group and I were designing the gear layout for the water bottle challenge, we did not know how to achieve the desired gear ratio. As a result, we just estimate the amount of gears we needed and hope for the best. However, that obviously did not work, therefore, we must think strategically on the gear ratio we must have. Thankfully, my peers told me what the desired gear ratio was.
In conclusion, I plan to take what I have learnt from this practical to my future projects like capstone. This knowledge can help me better design my prototype with gears, and make my whole prototype work in the future. Besides projects, who knows probably I might need to use this knowledge in my future workplace if i decide to become a mechanical engineer.
That's it for my blog, Thank you for taking the time to read this long blog, stay tuned for more blogs!
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