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): refers to the size of the gear teeth in the unit of mm. Larger the module number, larger the size of the teeth
Pitch circular diameter (PCD): 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 Gear 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. Gear ratio refers to the ratio of rpm (Rotation per min) of the driver gear to the rpm of the driven gear
The lower the gear ratio, the higher the output speed for a pair of gears
The higher the gear ratio, the lower the output speed for a pair of gears
When gear ratio is less than 1, the speed is greater
When gear ratio is more than 1,the speed is lower
Below is the relationship between gear ratio and torque for a pair of gears.
Torque refers to the measurement of twisting force, calculated as the product of circumferential force multiplied of the gear
Hence, The higher the gear ratio, the torque increases. The lower the gears ratio, the torque decreases
When gear ratio is greater than 1, torque is greater
When gear ratio is lesser than 1, torque is lower
3.Below are the proposed design to make the hand-squeezed fan better:
Proposed Designs:
- Attach a spring to the crank of the fan so than it its more efficient
- Replace the material of the gears with a smoother one to reduce gear friction
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).
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.Below is my Learning Reflection on the gears activities
Before actually starting the practical, I was required to look through videos talking about gears to allow myself to perform the practical much more effectively. I was really not looking forward to this practical as I was thinking to myself "Why learn about gears, I am studying chemical engineering make like no sense eh" Some more my knowledge of gears is really limited. So I had to look through the 4 videos that was provided in BrightSpace, they talked about gear module, PCD, gear teeth and gear ratio. These videos talked about how the gear ratio affects the torque and speed and also what are idler and compound gears. So TL:DR, the greater the gear ratio, the torque increases, the speed of the driven gear decreases. I found these videos relatively easy to digest and understand, so with all these new knowledge acquired, I was ready to take on the gears practical.
During the day of the practical, Mr. Chua handed us a worksheet relating to the practical and tasked us to do the question in the worksheet. These questions were about gear ratio gear module, PCD, gear teeth and gear ratio which was what was taught in the 4 videos. So my group and I had to issue doing these questions, it was smooth sailing activity.
After doing these question, we were now tasked to construct a lift using different gears to lift up a water bottle of 600ml. So our group had agreed that in order to maximize the torque of the gears we need a gear ratio that is very high. So, we promptly began our construction of the lift. During the construction of the gears, we decided to freestyle the construction without any calculations but with the knowledge to brute force a viable lift. That lead us to question if this gear ratio was able to generate enough torque to lift the bottle and had to pause multiple times to consider the positioning of the gears.
However, with enough skills, we managed to build our lift. But, we still had our worries as when before readying the water bottle for lift off. We decided to spin the driver gear for a bit and we realize that sometimes the driver gear gets stuck and had a lot of difficulty turning. So, when tying the string around the water bottle, we prayed for the best and started to lift the bottle up. With our prayers answered, we managed to carry the bottle up to 20cm. With that activity 1 was completed in the first try.
Thinking back, the driver gear had difficulty turning was maybe due to gear friction between the gears. This friction causes the set up to require even more force to turn the gears. These might also cause the theoretical rotations to be lower than the actual rotations required.
After completing activity 1, we proceed on to activity 2, where we had to make a hand squeeze fan. We were given a set of the deconstructed fan and we had to follow the guide in the worksheet to construct it. We had some difficulty assembling it as we had to guess the placement of some small parts and some connectors. However, we do know the placement of the gears provided where we had to make sure the speed ratio of the gears where optimal. With some of the intellectual guesses, we managed to assemble the fan and it managed to work. We proceeded to record the amount of actual rotations made in 1 crank using slow-motion. What my group noticed was that the actual rotation was slightly lower than the theoretical rotation calculated. This might be due to friction once again between gears.
Overall, from the two activities, I did not expect myself to enjoy doing this practical. It was a enriching and fun experience. This practical taught me a lot about gears and really helped me to broaden my knowledge. I hope that these concepts I learnt can help improve myself not as a chemical engineer but as an individual as well.
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