Gears

 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 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. Definitions and relationships between gear module, pitch circular diameter and number of teeth

Gear module (m): 
Refers to the size of the gear teeth. Its unit is mm, and the larger the module number, the larger the tooth size. Gears that mesh together has the same module size.

Pitch circular diameter (PCD): 
An imaginary circle that passes through the contact point between two meshing points. It represents the diameters of two friction rollers in contact and moves at the same linear velocity. Measured in mm.
Number of teeth (z):
Represents the number of teeth.
Relationship between gear module(m), PCD(mm), number of teeth(z):
m= PCD/z


2. Relationship between gear ratio(speed ratio) and output speed

Gear ratio is the ratio of speed between the input and output gears, thus its formula is:
Gear ratio = (Speed of input gear shaft) / (Speed of output gear shaft)
According to the above equation, gear ratio is inversely proportional to the output speed. Therefore, the higher the gear ratio, the lower the output speed of the gear arrangement, and vice versa.

Relationship between gear ratio(speed ratio) and torque

Gear ratio is also the ratio of torque between output and input gears, thus its formula is:
Gear ratio = (Output torque) / (Input torque)
According to the above equation, gear ratio is directly proportional to the output torque. Therefore, the higher the gear ratio, the higher the output torque of the gear arrangement, and vice versa.


3. Proposed design to make the hand-squeezed fan better

The obvious method of improving the design is by decreasing the final gear ratio to increase the output speed of the final gear connected to the fan blades. There are a few methods of doing this. 

One method is to increase the size of the input gears or decrease the size of the output gears. By following the formula stated in section 2, the gear ratio will decrease, thereby increasing the speed as well.

Another method is to create a larger compound gear system and use as few idler gears as possible. This allows for more complex arrangements of gears and can create a much low gear ratio, therefore increasing the speed.

Adding lubrication to the gears could also be another solution to this issue. Lubrication will prevent the gears from getting stuck as well as allow them to spin faster, thus allowing the fan blade to spin faster as well.

4. 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. Photo of the actual gear layout

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

        Measured winch radius = 5.7/2 = 2.85cm
        Circumference of wheel = 2π * 2.85 = 17.91cm 
        Distance covered by the wheel in 1 rotation/revolution = 17.91cm = 0.1791m
        Number of revolutions required = (1/0.1791m) * 0.2 = 1.12 revolutions

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

5. Learning Reflection

This practical was a very frustrating one at times, there were multiple reasons for this. One reason was that during the worksheet portion of the practical, my teammates and I were confused during the portion about calculating gear ratios. This being our first time learning and calculating gear ratio, we did not fully understand the formula for this. However, in the end, we did manage to finish up this portion of the practical properly and fully understood how to calculate gear ratio in the end.

Following that was activity 1, the creation of the gear system to raise the water bottle. This was a frustrating but fun activity. The reason is that for most of the time we were given to do this activity, we could not find any combination of gear arrangements that could have brought our gear ratio above 1.3. This was saved however by our teammate En Ting who found an arrangement that brought our final gear ratio to a much better 8.89. This made all of us very happy and excited but also wary. Due to our issues with gear ratio in the previous parts of the practical, we kept checking the gear ratio calculation to ensure that it was correct and did not have any mistakes. Overall, I'm quite satisfied and happy with our group's performance during this activity. Although we did not get the highest gear ratio possible, we still did get a satisfactory 8.89 which was still a much better improvement from what we had at first. This activity helped me to better understand the importance of compound gears when making any type of gear arrangement.

After this, we proceeded to activity 2, which was to put together the 3d-printed parts of a hand-held crank fan. This was a fun but frustrating activity. The reason for this is that no matter how I put the gears together, they would always get stuck and the crank would not be able to move back into its uncranked position after being pushed in. This caused the fan to have malfunctions frequently and could not move for extended periods until we take it apart and redo the system. In the end, we could not really get it to work properly, but were still able to make it work somewhat. During this activity, I learned that lubrication is a very important aspect of gear arrangements in the working world. Without things like grease or other types of lubrication, a lot of systems in the world would not work as the parts would be too stiff to move properly.


This brings this page of my blog to an end, I'll see you next time post on here for my course in CPDD!