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:
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.
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): It refers to the size of the gear teeth and the unit is mm. The larger the module number, the larger is the size of the teeth. Gears that mesh together have the same module.
Pitch Circular Diameter(PCD): It refers to 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.
Relationship between Module (m), No of teeth (z) and Pitch Circular Diameter (PCD):
m= PCD/z
2. Below is the relationship between gear ratio (speed ratio) and output speed for a pair of gears.
To understand the relationship between gear ratio and output speed, I first need to define gear ratio and output speed.
Gear ratio (speed ratio) of a gear train is the ratio of the angular speed of the input gear to the angular speed of the output gear. It can be calculated using a ratio of the teeth, radius, diameter or circumference of the gears.
Gear Ratio = number of teeth of the follower gear/ number of teeth of the driver gear
Torque is a measure of the force that can cause an object to rotate about an axis. It is calculated by multiplying the magnitude of the force with the distance to the axis of rotation.
The higher the gear ratio, the lower the output speed, and vice versa
Below is the relationship between gear ratio and torque for a pair of gears.
The higher the gear ratio, the higher the torque, and vice versa
3.Below are the proposed design to make the hand-squeezed fan better:
During the practical, my group had an activity where we had to assemble a hand-squeezed fan. Below is a slow-motion video of the fan we assembled.
One issue we had was that when the handle was pushed maybe two-thirds of the way into the fan, it would just get stuck and the arm would have difficulty moving unless we really put a lot of force into it. To combat this, I think using a spring instead of an arm as the crank to push the gears would help. By using a spring, it would remove the problem of not having enough force to push the gear and keep it moving.
Another potential modification could be that rearrange the gears within the fan to lower the gear ratio, hence increasing the speed of the fan.
4.Below are the description on how my practical team arranged the gears provided in the practical to raise the water bottle.
a. Calculation of the gear ratio (speed ratio).
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b. The photo of the actual gear layout.
c. Calculation of the number of revolutions required to rotate the crank handle.
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d. The video of the turning of the gears to lift the water bottle.
5.Below is my Learning Reflection on the gears activities
Honestly, I was rather confused when I found out we had an activity on gears. As in, I didn't realise I signed up to be a mechanic?? Throughout the whole of the pre-practical prep, which was basically just watching a few videos, I was really contemplating when I would be using gears in the future, like where would gears belong within a distillation setup. Regardless, I studied the videos and learnt all about gear module, PCD, gear teeth and gear ratio.
During the experiment, we first had to fill up a worksheet as a group to ensure that we had watched the videos and knew what we were about to do. All in all, although we ran into some issues such as being confused about the phrasing of some questions, we were able to answer all the questions.
In the 1st activity, we were tasked to use gears to build a setup to lift a 600ml water bottle 20 cm off the ground. We decided that we would start building the setup right away, without making any calculations. Midway through, we started to be concerned that we might not have considered the gear ratios of the gears we were arranging and we had to stop multiple times just to make sure the torque was enough. We did this by testing if the gears would move when we turned the driver gear whenever we added a new gear. Through this slow process, we were able to complete the setup. However, we were still concerned as our setup seemed rather flimsy and we didn't know whether it could truly hold the weight of the 600ml water bottle. Regardless, we decided to just tie up the water bottle to the last gear and hope that it worked. Somehow, with our haphazardly built setup, we were able to complete the activity and lift the bottle 20cm off the ground.
Although we were able to lift the bottle off the ground, we really struggled to turn the driver gear at certain points due to the fact that our setup was not optimised for reducing factors such as friction between the gears. therefore in reality we would have to turn the driver gear more times than calculated.
During the 2nd activity, we were tasked to build a hand-squeezed fan, using the deconstructed parts of the fan. We had to follow the guide in the worksheet which had a diagram of roughly how to build it. However, we still had some trouble trying to find which gear fit into which part of the fan. Eventually we were able to build it and test it out. While testing it, we realised that the fan would get jammed at certain points, at which point we would have to push it with even more force to get it to keep moving. This may have also been connected to the same factor of friction between the gears of activity 1.
Overall, I had fun and learnt quite a lot about gears from this lesson. With this knowledge in hand gained through a very engaging practical, I hope that I will be able to apply this during the future CPDD CA2 and my future FYP.
Here is a picture of my group posing with our working gear setup :D
Thanks for reading my Blog!
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