Gears

 Hi, I am back with my 2nd blog- GEARS!!!!

1. These are the definition of gear module, pitch circular diameter and the relationship between gear module, pitch circular diameter and number of teeth:

Module (m) is the unit of size that indicates how big or small a gear is. It is the ratio of the reference diameter (pitch circular diameter) of the gear divided by the number of teeth.  

Thus:  m = d/z (Module = Reference diameter/ Number of teeth )

Pitch (p) represents the distance between teeth, and since a larger pitch means a larger tooth size and a smaller pitch means a smaller tooth size, the pitch can be used to represent the tooth size.

The pitch circle of a gear corresponds to the outer circumference of the friction wheel (gears can be thought of as friction wheels with teeth attached) and is the reference circle for determining the pitch of the gear teeth.

The circumference of the pitch circle (πd) is its diameter (pitch circle diameter = d) multiplied by the pi π. The pitch is obtained by dividing the pitch circle circumference by the number of teeth (z).

p = πd / z

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

Gear ratio = number of follower gear teeth / number of drive gear teeth.

In a small/large gear set-up, when the small gear has made a full rotation, the large gear will not have yet completed a full rotation. Thus, the smaller gear makes more revolutions in a given time, rotating at a faster pace than the larger gear. 

For two given gears, one of number of teeth A and one of number of teeth B, the speed ratio (gear ratio) is as follows:

(Speed A x Number of teeth A) = (Speed B x Number of teeth B)

Therefore the speed ratio is inversely proportional to the gear ratio. If the speed ratio is larger than 1.0 (gear ratio is less than 1), then the gear pair is operating as speed increaser. This means that the lower the gear ratio, the higher the output speed for the pair of gears. If the speed ratio is smaller than 1.0 (gear ratio is higher than 1), then the gear pair is operating as speed reducer. This means that the higher the gear ratio, the higher the output speed for the pair of gears.

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

The gear ratio also expresses the ratio of the output torque to the input torque. The higher the gear ratio, the higher the torque multiplier, the higher the output torque of the follower gear. The lower the gear ratio, the lower the torque multiplier, the lower the output torque of the follower gear.

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

My group and I are supposed to arrange the gears of the hand-squeezed fan so that the hand-squeezed fan can spin faster. We had to calculate the gear ratio of each contact point and multiply them to obtain the lowest gear ratio, so that the speed of the fan is at its fastest speed.

Here's a photo of the interal and external body of the fan

 Sketch and calculations of the proposed design for the hand-squeezed fan

Video of the fan in slow-motion

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.

The arrangement of the gear train are as follows:

1. Gear 50T with handle

2. Gear compound 20T-40T

3. Gear Idler 30T

4. Gear compound 20T-40T

5. Gear Idler 40T

6. Gear compound 20T-30T

7. Gear compound 12T-40T

8. Gear 40T with winch

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

Circumference of winch = 2πr = 2(π)(31.5) = 197.92

Revolutions of winch = 200/197.92 = 1.01

Revolutions of driver  gear = 1.01 × 0.8 = 0.81 revolutions 

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

5. Below is my Learning Reflection on the gear activities

I enjoyed this week's practical because I have the opportunity to assemble and arrange the gears with my groupmates. Before the practical, I have to watch 4 videos about gears. I learnt about the gear ratio. However, due to my short attention span, I somewhat did not grasp the knowledge of how gear ratio affects the speed and torque, which then cause me to wait for this week's practical to fully grasp the knowledge. The first activity, lifting the water bottle, is definitely the highlight of this week's practical. We arrange the gears first than we screw and nut them on the board. However, it is the most challenging activity we did because after we finish screwing and nutting the gears on the board we have to test it to find out whether we can turn the handle easily. After we did our tests, we need to find out the problem. For example, some part of the gear teeth was not touching very close to each other, causing the rest of the gear train to not move. Therefore, we have to reconstruct the whole gear train which then caused us to spend a lot of time to reconstruct the gear train. That is why for activity 2 we only get Fion and Isabella to do it since it is the easier activity. Despite the challenges we faced for activity 1, we managed to finish both activities on time. Overall, it was a fun activity and I became somewhat interested about gears.