Gears

 hi everyone, 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:

1. Calculation of the gear ratio (speed ratio)

2. The photo of the actual gear layout.

3. Calculation of the number of revolutions required to rotate the crank handle.

4. 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:

Definitions

Gear Module: Gear module refers to the size of one teeth on the gear, with the unit being mm.

Pitch Circular Diameter: The pitch circular diameter is the imaginary circle that passes through the contact point between two gears that are meshing, and it represents the diameters of the two friction rollers in contact and it moves at the same linear velocity.

Let gear module be m, Pitch Circular Diameter be PCD, and number of teeth be z.

PCD = m x z

Thus, as the number of teeth increases, PCD would increase. As the module or the size of the teeth increases, PCD would also increase. This is because the increase in either the number of teeth or the increase in the size of the teeth would cause the diameter of the circle created by passing through the contact point between the two gears to increase.

2. Below is the relationship between gear ratio (speed ratio) and output speed for a pair of gears.

As the gear ratio for a pair of gears increases, the output speed of the gears would decrease. This is because the gear ratio is calculated by taking the number of teeth on the follower gear and dividing it by the number of teeth on the driver gear. As a result, the speed at which the follower gear would turn would be lower with the increase in the number of teeth in the follower gear, and thus, the gear ratio and the output speed are inversely proportional.

Below is the relationship between gear ratio and torque for a pair of gears.

When the gear ratio increases, the torque would decrease. This is because an increase in the gear ratio would cause the speed of the output to be decreased, and with the decrease in speed, the force that would cause the rotation of the gear would also decrease. Therefore, gear ratio and torque are inversely proportional.

3. Below is the proposed design to make the hand-squeezed fan better:

By increasing the gear ratio in the hand-squeezed fan, the number of rotations made per press of the handle would increase. This would allow for a higher efficiency.

Another way to make the hand-squeezed fan better would be by increasing the length of the connecting piece between the handle and the gears. As the fan often got jammed after only 1 press of the handle, due to the connecting piece resting in a horizontal position and not responding to any press of the handle, by increasing the length of the connecting piece, this issue can be avoided.

4. Below is the description on how my practical team arranged the gears provided in the practical to raise the water bottle.

1. Calculation of the gear ratio (speed ratio).

   
   

   Gear ratio = 40/30 x 40/20 x 40/40 x 30/20 x 40/30 x 30/40 x 40/30 = 5.333333                  = 5.33 (3 s.f)

2. The photo of the actual gear layout.

3. Calculation of the number of revolutions required to rotate the crank handle.

The bottle needed to be lifted 200 mm off the ground.

1 full rotation of final gear = πD = π x (22)

No. of rotations of final gear = 200/π(22) = 2.894

Gear ratio = Input/Output

5.333 = Input / 2.894

Input = 5.333 x 2.894

Therefore, Input rotations = 15.433 = 15.5

Number of rotations needed by the input gear (gear with handle) for the bottle to be raised 200mm: 15.5 rotations

4. The video of the turning of the gears to lift the water bottle.

5. Below is my Learning Reflection on the gears activities

When I first heard we were doing gears for our next practical, I was actually very confused, as I remembered signing up for a course in Chemical Engineering, not something like DEEE or DARE or anything else mechanical related. However, my past experiences with working on problems related to moving parts in Physics when I was in secondary school have taught me that when executed well, practicals like this could actually be very fun, so I found myself looking forward to this practical.

To start, we actually had to go through some learning packages on gears before we could actually start carrying out the practical. It was through the videos in the learning package that I realised that I did not know as much about gears or concepts like torque, gear ratio, or how factors like the number of teeth in a gear affect the speed of the output as I thought. Although I was quite confused and intimidated by the prospect of having to learn all these almost foreign concepts in a short amount of time, I pushed through and brushed up on as much knowledge as I could before the practical.

When we entered the lab to start on our practical, our lecturer passed us a worksheet to fill up, which contained simple questions on some concepts that we learnt about in our e-learning packages, as well as some other questions where we not only had to apply what we learnt, but we also had to have a deep understanding of what we had learnt. Although I struggled with the concepts initially, I found myself getting the hang of how the calculations for such questions were done, and so the simpler questions were done rather quickly.

After doing some refresher questions, it was time to get into the actual practical, where we were required to perform two activities. The first was constructing a compound gear train to be able to lift up a bottle containing 600ml of water. We also had to perform calculations to determine the amount of force that would be provided to lift the bottle. While doing this activity, I found it very difficult to visualise how we were supposed to create the most efficient gear train while making use of every gear that was provided to us, as I find it difficult to visualise such diagrams in my head before actually creating it. On top of that, it was very hard to actually put the gear train together, as the gears that were provided to us, although they looked pretty good, were actually quite unstable when it came time to turn the gear train. The length of the screws given to us were also not enough to actually securely hold the gears in place, so our first design of the gear train was actually not feasible due to the difference in height between gears on different levels.

Although I found the process of constructing the gear train, as well as the process of coming up with a feasible and efficient gear train to be quite tedious and irritating, I am grateful for my groupmates, who made the whole experience worthwhile, as even though we were constantly set back by our limited resources and our plans that did not come to fruition, their company and constant jokes made it more bearable and actually quite fun. It was also through this activity that I realised that we should always be prepared fo plans to fall through and not turn out the way we want them to, as at the start of this activity, my group was very confident in our initial design, painstakingly performing calculations to find the most optimal setup, only to realise that our design was not feasible to create with what little resources were provided to us, and we were so devastated that we almost lost all motivation to keep going. From this experience, I learnt the importance of being flexible and being willing to change plans on the fly. In the end, my group did eventually manage to pull through and come up with a somewhat solid design that was able to output a decent amount of torque, which was sufficient to lift up the bottle.

two very handsome men setting up our gear train 😍

For the second activity, we were required to construct a small hand-powered fan that would be able to be activated with a simple press of a handle. Even though this activity seemed rather simple compared to the first activity, as all of the parts for the fan were already provided to us, and we were also given somewhat in-depth instructions on how to put the fan together, I still found it satisfying, as it gave me the same dopamine rush as putting together Lego sets back when I was a child. 

me reliving the childhood I never had 😔

After I had finished setting up the fan, I pressed the handle on the fan, but to my horror, the handle got jammed immediately, which was pretty funny. I then realised that the gears that I put into the fan were out of alignment, which caused the whole thing to stop functioning after one press. Although I was quite disappointed, I sucked it up, took the whole thing apart and rebuilt it. After carefully ensuring the whole setup was secure, I pressed the handle, and thankfully, it started to produce a small gust of wind. This wasn't the first time I had to do something like this, as similar to the first activity, where our initial design was not functional and we had to proceed to undo every bit of hard work we had just done, restarting completely from scratch. I had learnt to be patient with my creations and not be too careless in handling them.

However, although I do say that I learnt to be patient with my creations, when deconstructing the fan, I actually broke the piece attached to the fanblade after pulling on it too hard, so... 

Anyways, as a whole, I would say that this practical was somewhat of a success, even though my group struggled with almost every step of the process. I really learnt a lot about how gears worked while carrying out this practical, and I do feel that it would be helpful in the upcoming CA2 where we have to come up with an original design to solve a problem, with my group choosing to do one on a carbon monoxide detector which then turns on a fan to vent out said carbon monoxide. I think I will be able to apply what I learnt in this practical in the upcoming CAs, and even though this has been somewhat of a bad first impression on the use of gears, I do look forward to making use of them more in the future!