Blog Entry 2: Gears
For this blog entry on gears, I feel will be relatively short. There is not much to talk about other than the basic terminologies. I will be going through how gears work, the concepts and calculations behind gears, as well as what was done during the practical session.
So firstly, a gear is basically just a circle or ring with teeth. The teeth are the most crucial part of the gear as it is what enables the gears to mesh together and ultimately turn.
Gears come in different sizes and putting two or more gears together create what is called a "Gear Train". There are mainly two reasons one would put a big and small gear together and that would be to achieve a force multiplier or speed multiplier. I will elaborate on these concepts later on.
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The gear that is being turned is called the "Driver" while the gear being turned by the driver is the "Follower". In most cases when the driver and follower are meshed together, the follower will rotate in the opposite direction of the driver. This is where the "Idler" comes into play. The idler is an intermediate gear put in between the input gear and the output gear. It mostly allows the two gears to rotate in the same direction.
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Force multiplier:
So now imagine this situation (or just look at the diagram above of the big and small gear), where the small gear is the driver. You will notice that the small gear will be able to finish one revolution faster than the big gear. This is a force multiplier combination where the main focus of the output gear (big gear) is to increase the amount of force exerted. E.g. You only require 1N of force to rotate the small gear but the big gear is able to exert a force of 10N.
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Speed multiplier:
From the previous example, it can be inferred that if the force multiplier allows the input force to increase at the output, the speed multiplier combination allows the output speed to be much larger than the input. Now the big gear will be the driver. You will notice that the driver will rotate slower than the follower. That is practically it. If the driver rotates at 10rpm, the speed multiplier can cause the output to rotate at 100rpm, for example. The downside of the speed multiplier is that more force will required to turn the driver.
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Gear ratio:
The gear ratio is a very useful piece of calculated data when it comes to gears. It can be used to calculate the amount of torque, number of rotations, number of teeth, and sizes of the relevant gears.
r refers to the radius
T refers to the torque
z refers to the number of teeth
u refers to the speed
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As seen, the different values can be easily calculated once the gear ratio is obtained. It is also worth noting that for radius, torque and number of teeth, the gear ratio is always output (follower) over input (driver) but when it comes to speed, it is input over output.
I mentioned previously about idlers. In the above image, an idler can be seen. When it comes to a gear ratio of a gear train with idlers (one or more idlers) they do not affect the gear ratio between the input and output gears. In the context of this image, it can be said that the gear ratio is 0.5 reason being because the gear C has 8 teeth and the gear A has 16 teeth. The number of teeth of the idler gear does not affect anything, as already mentioned.
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Other gear measurements is the gear module and pitch circular diameter.
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Gear module:
Gear module refers to the size of the gear teeth. Two gears can only mesh together if they have the same gear module. It is usually measured in "mm" and the larger the gear module would mean the larger the teeth. Thus,
Gear module, output = Gear module, input
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Pitch Circular Diameter:
This is the imaginary circle that passes through the contact points between two gears. It is essential a circle at the circumference of the gear if the diameter was measured from one contact point to another.
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The gear module can also be defined as the length of pitch circular diameter per tooth. Therefore,
Gear module = Diameter / Number of teeth
The above video is the hand-powered fan the group had made in activity 2. On the right is the sketch of the design. The gear ratio of this arrangement is about 0.101 and is shown in the video when the fan spins around 10 times with one crank.
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One of the ways to improve the fan, so it can spin more is decrease the size of smaller gears on the compound gears. This will result in a larger gear ratio. Ultimately, the output will be a fan with a higher rotation per minute. Speed multiplier. (Refer to image below)
The group did not take a photo of the actual layout for activity 1 but this is the video of Clive and myself cranking the bottle up to verify our calculations. Below is the sketch of the gear train arrangement. It took about 4 turns fo the bottle to be lifted by 20cm.
As seen in the calculation, the gear ratio is 4.
The calculated number of turns of the crank was about 11.6 which is off from the actual number of turns, 8.5. I feel like this could be due to an error in measuring the radius of the gear as when I measured it, I did not really have a clear contact point of the gear. Another possible reason for the error could be due to the poor turning quality of the gears as I did not fully tighten the bolts when fitting the gears.
I think most of the trouble of this practical was from activity 1.
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I believe during the time of the activity, most, if not all, of the members in the group did not fully understand how to apply the concepts of gears. There was a confusion on how to crank up the bottle with little force. We were not sure on whether the gear ratio should have been more than 1 or less than 1. Eventually, the group did begin to understand how gears worked and apply better the concepts. However, we did run out of time so we were not able to form another gear train with a better gear ratio (larger gear ratio) to crank up the bottle.
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Now that I understand better gears, here are some changes I would have made if given more time.
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The size of of the crank:
Initially, the smaller crank of 30 teeth was used but due to all the confusion the finalised design was to use the 50 teeth crank. We tested out both cranks and found that the 30 teeth crank required 13.5 cranks while, as mentioned previously, the 50 teeth crank took 8.5 cranks. The more number of cranks would be desired in this case. Below is a video of us trying the 30 teeth crank.
Of course, even if we did use the gear train arrangement to get a gear ratio of 13.5, it is still possible to obtain a higher gear ratio as I have asked around and found some groups obtaining a gear ratio of 26.
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I think if given another opportunity, the group would do better job in a similar activity to this or obtain a gear ratio of 26 as well. Although, that opportunity did come about in activity 2 where I like to believe that we did better.
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For activity 2, I feel like since everyone already knew how to relate the theoretical aspect to the practical aspect, it was quite easy to come up with a very low gear ratio with the given gears.
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However, I think if activity 2 was done under the same context as activity 1 where all of us did not know what we were doing at first, I think the group still would have done better for this case. I think big part of what contributed to the group performing relatively badly for activity 1 was because it could seem quite intimidating to have to utilise so many gears and having to calculate a bunch of things but in activity 2 the number of gears required is significantly less. In the end, it all comes down to self management skills.
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After having thought about it, not only did I learn about how gears work and their applications but I also learnt something about myself and my groupmates. I learnt that we all need to learn how organise our inner thoughts as to not get so intimidated and distracted from the task at hand so we can efficiently get the job done. I think this is definitely something I would look out for in future practicals and work with them.