In this edition on Gears ⚙️, I shall be documenting and reflecting on my experience with the Gears Practical.
Let's go through a quick run-thru on the background of Gears before reading this blog page.
What are Gears?
Gears are circular teethed wheels whose main purpose is to ease stress by moving loads with minimal difficulty.
What comes to mind when Gears are mentioned could be something like...
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| Or even this... |
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This!!
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That is exactly what they are. In this instalment of my CPDD Blog, I shall be documenting and explaining the function and application of gear train designs.
On the surface, gears seem like such simple working tools used in many daily operations.
However, in order for gears to function well, their arrangement actually has to be designed intelligently.
Gears work together to simplify movement of loads.
It is truly a marvel how mathematicians and mechanics were able to design systems built on gears to revolutionise the world and its industries. π€―
A common but complex daily example would be the bicycle! Many use the bicycle as a reliable form of transport. π²
Its movement is based on the gears within its complex gear chain.
Hence, this brings us to the study and objective of this lesson on Gears, the movement and effect of gears, and how to apply gears into design.
Gear Train
All gear trains consist of 2 gears in general, the Driver and Follower
Driver: Input gear
Follower: Output gear
The driver moves in the opposite direction of the follower, e.g. If the Driver turns clockwise, the Follower turns anticlockwise.
Therefore, in some cases, a gear is placed in between both gears to allow Driver and Follower to synchronise in the same direction.
This is called IDLER gear.
In the subsequent bulk of this page, I will describe:
The definition of gear module, pitch circular diameter and 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 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.
1. Definition of gear module, pitch circular diameter and relationship between gear module, pitch circular diameter and number of teeth
Terminology and Definition | Photo to illustrate description |
Gear module (m)
Size of gear teeth. (tooth size)
Unit of module is mm.
Gears that mesh together have the same module, m. | 
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Pitch Circular Diameter (PCD)
Imaginary circle which passes through the contact point between two meshing gears.
It represents the diameters of two friction rollers in contact that move at the same linear velocity.
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Relationship between Module (m), Pitch Circular Diameter (PCD) and Number of Teeth (z)
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2. Relationship between - gear ratio (speed ratio) and output speed
Taking a basis of a pair of gears ⚙️⚙️,
Relationships | Description (vice versa) |
Gear ratio (speed ratio) and output speed
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As gear ratio increases, the output speed of a pair of gears increases
Higher gear ratio = Higher output speed
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Gear ratio and torque | As gear ratio increases, torque decreases
Higher gear ratio = Lesser torque
Alternatively,
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From this section, we understand that Gears can be modified to achieve 2 main function groups
3. How I can design a better hand-squeezed fan, including the sketches
To design a better hand-squeezed fan compared to the one provided during the practical.
Firstly, analyse the motion of the provided fan.
The fan's working mechanism is constructed from a compound gear train.
The fan requires high torque to operate and produces a decent speed output.
Secondly, the objective of the hand-powered fan is to maximise its speed output for improved airflow for cooling
Hence, the gear train constructed should have a minimal gear ratio to achieve the desired outcome.
That means larger driver gears and smaller follower gears.
Sketch of Unmodified Design
The number of teeth in the gear can be replaced to achieve a lower speed ratio for a better hand-squeezed fan design.Driver gear teeth can be increased or kept constant, while Follower gear teeth can be decreased or kept constant.
The change of either variable will allow the design to achieve a higher speed output.
For a more compact design, I decided to decrease the number of gear teeth for the follower gears. (Having larger gear teeth will cause the product to be larger in size)
Sketch of Modified Design
The new gear ratio for the design system will be lower, allowing the fan to spin faster, and cooling the user better. Hence, a better design.
4. How my practical team arranged the gears provided in the practical to raise the height of the water bottle, consisting of:
a. Calculation of gear ratio (speed ratio)
b. Photo of actual gear layout
c. Calculation of number of revolutions required to rotate the crank handle
d. Video of the turning of the gears to lift the water bottle
a. Calculation of Gear ratio (speed ratio), GR
Once again, to recap,
Outgoing gear / Incoming gear
In calculations, we always refer to the gears which are meshing against each other to derive the gear ratios, especially for compound gear trains, it is important to make a clear distinction, as it may be confusing to determine the driver, follower and idler.
GR 1: 40/30
GR 2: 30/12
GR 3: 40/20
GR 4: 40/20
GR 5: 40/20
Total Gear Ratio = GR 1 x GR 2 x ... GR 5
Total Gear Ratio = 26.667
Explanation:
High Gear ratio = Low Torque input needed to turn the crank (GOOD); Less Speed output
Hence, the high gear ratio calculated would theoretically provide a strong mechanical
advantage when hoisting the water bottle above ground level
Lower torque is required to turn the crank. (High torque output multiplier)
b. Photo of the actual gear layout
The team leveraged the situation of the compound gear train clause; since we were tasked to use all the gears provided, we flipped some compound gears back facing to obtain the best theoretical gear ratio possible.
Since Gear Ratio (GR) = Output/Input
Our team used the sequence of small gear drivers with large gear followers to obtain the best possible theoretical gear ratio.
c. Calculation of the number of revolutions required to rotate the crank handle
Circumference = 2πR
Diameter of winch follower = 58mm
Circumference of winch = 2π(582)=182.21 mm
Height needed to be raised = 200mm
Revolution of winch follower = 182.21/200 = 1.097
Revolution of crank needed = No. of revolutions of follower x Gear ratio = 1.097 x 26.667 = 29.3 revolutions
d. Video of the turning of the gear train to hoist the bottle
The bottle lifted upwards of a meagre few centimetres, despite the theoretically high gear ratio concept. Why is this so? What happened? Could the bottle be too heavy?
Read Section 5 on my learning reflection on why our gear arrangement failed the trial run.
5. My Learning Reflection π€π
This practical on gears was a very hands-on and in-depth introduction to the working mechanism of Gears. Previously, in CP5065 ICPD, I learned about working mechanisms, and gears were introduced as one of the six common functional mechanisms. It is only now that we learn how gears can be fully utilised to fulfil a desired functional objective.
Through this practical, I have gained an appreciation towards Gear mechanism design.
Activity 1 ⚙️π
I felt that it was very hard to rack our brains to formulate the best possible gear layout that corresponds to the highest gear ratio desired.
Based on our understanding, we attempted to alternate the gears from low drivers to high followers, since this would yield a higher gear ratio generally.
We also took the hint from Dr Noel to make use of the compound gear train formation. Hence, we flipped and played around with the positions of the gears to maximise our gear ratio.
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| Gear on the left side can be seen as back-facing |
Ultimately, after the tedious calculations for the gear ratio, we derived a relatively high gear ratio of approximately 27.
We then got to implementing the layout onto the physical board. However, it was only after we attached everything onto the board with our Allen Keys, that I realised that the gear head attached just before the winch was blocking the pathway for the rope and its knot to rise and bunch up.
I pointed this complication out early on before we fully committed to the attempt. However, my teammates turned a blind eye either because they believed the idea would still be useful for theoretical study since it still yielded a high gear ratio, or because they did not catch my multiple reminders. πΏ
Due to time constraints and out of options, we decided to use the gear arrangement nonetheless, especially since theoretically, it would be able to achieve our desired function.
With reference to the video in section 4, the water bottle can be seen rising up until the rope's knot is caught within the final gear's head. The gears were also able to rotate smoothly, due to the high gear ratio which results in low input torque needed to turn the crank.
Despite the gear train pulley system working well for a few good revolutions, I would have loved to watch a successful attempt done by our team.
However, the product design learning journey is not about whether an idea works, it is about whether the idea's rationale is logical.
In this sense, since our theory and the physical product gear train showed an understanding of what gear ratio level we needed for this activity, we gained the knowledge and are able to understand gears from better angles and standpoints.
During this practical and the post-practical test, I struggled with understanding how to calculate the number of revolutions, as I did not have an adequate understanding of it.
However, after viewing calculations done by my teammates, I was able to understand and calculate the revolutions needed for an input gear based on the revolution produced by the output gear and vice versa.
Ultimately, from observation, almost all calculations and information are based on and well related to the speed ratio.
Activity 2 ι£ζ
I got very frustrated while attempting to place together the hand-squeezed fan, then went on to Youtube at a later time and heard from the speaker that the design was easy to put together, and even anyone's grandmother could do it.
During the assembly, I spotted an error in the manual's sketch.
The 3rd Gear from the left has to be facing backwards, however, in the sketch, it was upward facing.
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Error
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| Correct Diagram to construct |
I also broke the top gear portion attached to the fan propeller while trying to detach it from the shell casing. I am reminded to be careful with 3D printed parts as the material used to construct them is fragile.
I learned that the fan handle will get jammed if it is in a squeezed position since the fan works on inertia. When in the closed position, it will tend to stay in the closed position. We will have to reset it to the opened position by manually turning the propeller. Then only the gears can spin and a continuous motion of squeezing the handle and turning of gears is started.
The fan can be seen jammed up in this clip
In conclusion, after the experience from this practical, I have gained the applicational skill of gears to be used as a working mechanism.
I have gained a better appreciation of Gear mechanism design, and its application in our world.
This begs the answer to the question, perhaps gears were used in the construction of pyramids in Egypt. π½⚙️π«
I am certain that this knowledge could be a beneficial mechanism for my team's Design Thinking project, the Tea Maker. π΅π€
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