Welcome back to my third blog! I am excited to share with all of you about the content that I will be covering in this blog-----------------GEARS! Sounds familiar? In fact, some of my viewers from my previous blogs on blogger have studied what it is about. Without further ado, LET'S JUMP RIGHT INTO IT!
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
Gear module is defined as the unit of size that indicates how big or small a gear is. It is the ratio of the reference diameter of the gear divided by the number of teeth. Mr Chua told us that it reflected the size of each teeth on the gear.
Pitch Circular Diameter (PCD)
The relationship between gear module, Pitch Circular Diameter and number of teeth:
GEAR MODULE = Pitch Circular Diameter/ Number of teeth
2.Below is the relationship between gear ratio (speed ratio) and output speed for a pair of gears.
Gear ratio |  |
Speed ratio | 1/ Gear ratio |
Relationship between gear ratio and output speed for a pair of gears
output speed = speed ratio x input speed = input speed / gear ratio
Below is the relationship between gear ratio and torque for a pair of gears.
Definition of torque
Torque, also called moment of a force, in physics, is defined as the tendency of a force to rotate the body to which it is applied.
Relationship between gear ratio and torque for a pair of gears
3.Below are the proposed design to make the hand-squeezed fan better:
Before I showcase the proposed design, I would like to upload a video and a sketch of our initial hand-squeezed design.
The overall gear ratio of the original hand-squeezed fan can be calculated as follows:
= (10/20) x (9/20) x (9/20) = 0.10125
To make it better, I believe that we need to make the fan achieve a higher output speed. Therefore, a greater speed ratio is required and by the definition of speed ratio, a smaller gear ratio is needed. To achieve a smaller gear ratio, we can either increase the number of teeth of the driver gear or decrease the number of teeth of the follower gear.
In the meantime, a bigger fan will create a stronger airflow and thus, cool down the body temperature in a faster rate due to the effect of evaporation of hot air.
With all these concepts in mind, I proceed to come up with the following design:
The overall gear ratio of the improved version of the hand-squeezed fan:
= (10/40) x (9/20) x (5/20) = 0.028125 Gear ratio between the improved and the original = 0.028125/0.10125
= 5/18 Speed ratio between the improved and the original = 1/gear ratio = 3.6
Therefore, the improved fan will have a rpm that is 3.6 times faster than the original fan. By installing a fan that is twice the size of the orignal one, the new fan will be much more powerful.
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).
Unlike Aminur's group which is extremely ambituous, my group elected to go for the safest design due to time constraints. We let all the gears except for the input gear and the output gear be idlers. As a result, our gear ratio will be much smaller than others but we spent less time constructing the system.
Gear ratio:
= number of teeth in the driven gear / number of teeth in the driver gear
= 40 / 30
= 1.33 ( to 3 s.f.)
b.The photo of the actual gear layout.
c.Calculation of the number of revolutions required to rotate the crank handle.
Given:
Diameter of the winch: 22 mm
Distance travelled by the water bottle: 200 mm
Number of rotation completed by the output gear
= (200) / ( 𝝅 x 22 )
= 2.89
Number of the revolutions required to rotate the crank handle
= gear ratio x number of rotation completed by the output gear
= 1.33 x 2.89
= 3.84 ( to 3 s.f.)
d.The video of the turning of the gears to lift the water bottle.
5.Below is my Learning Reflection on the gears activities
I personally believe that this practical is very fun as everyone in my team had the chance to perform some hands-on activities while learning some useful concepts on gears as well. After watching the videos on Youtube the day before the practical, I had equipped myself with the knowledge on gear ratio, mechanical advantage, idler and so on. I feel like it's very important to prepare ourselves before the practical, as it makes us feel more calm coming into the workshop and when Mr Chua briefed us on the concepts, it strengthed my understanding too.
During the practical, I learnt the definition of module, which is essentially the size of the teeth in the gear. I understand how to apply Pitch Circular Diameter (PCD) and the relationship between gear ratio and speed ratio. Apart from these technical terms, Mr Chua also explained us the difference between a simple gear train and compound gear train. The main difference is compound gear train has at least one shaft that holds two gears of different sizes.
The most amazing part was making use of compound gear train to increase/decrease the gear ratio. I was not aware that gears could really make such an impact in our daily life. For example, in activity 2, with the use of two compound gears, the gear ratio was decreased to 0.10125, which gave a high speed ratio and enabled the fan to turn in a very fast pace. Another good example would be witnessing Aminur's group successfully built a gear train with a gear ratio of 26.25!. Consequently, when they lifted up the water bottle, they only needed a small smount of strength to complete the task. This is practical really made me appreciate the beauty of mechanics.
One of the major findings of the practical is upon realising the inaccruacy between the theorectical revolutions and the actual revolutions. In activity 1, after discussing with my teammates, we realised that friction played a big part in it. The friction between gears and gears and the board will result in more energy required to overcome them. In activity 2, for instance, the actual number of revolution was 9.88 while the theoretical revolution was 9.67. This is due to the effect of air resistance generated when the fan turns and the friction between the gears.
For my lovely team, I enjoy working with all of you very much as we display great chemistry during the activities. We managed to finish both activities in time as we split our team in 2 small groups to complete both activities separately. A big shoutout to Jian Lun and Brice for building up the gears to lift the water bottle in a short period time. Also thanks to Joel who was good at sketching the gear layout. Last but not least, our video recorder, Yu Han, who helped us record the videos on both activities. I look forward to working with you all in the furure experiments.
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