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 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.

  1. 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. The larger a module number, the larger is the size of the teeth. Gears that mesh together are have the same module. 

Pitch circular diameter (PCD): Refers to the imaginary circle that passes through the contact point between two meshing gears. It represents the diameter of two friction rollers in contact and moves at the same linear velocity.

Number of teeth (z)

Relationship between the 3 variables are, Gear module = Pitch circular diameter/No. of teeth
                                                                                    m = PCD/z

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

As the speed ratio increases, the output speed for a pair of gears decreases. Gear ratio = Number of teeth of follower gear/Number of teeth of driver gear. If the speed ratio is >1, the follower gear is larger than the driver gear, so the output speed will be lower. If the speed ratio is <1, the driver gear is larger than the follower gear, so the output speed will be higher.

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

As the speed ratio increases, the torque for a pair of gears increases. If the speed ratio is >1, the follower gear is larger than the driver gear which increases the torque. If the speed ratio is <1, the driver gear is larger than the follower gear which decreases the torque.

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

The proposed design is to make the squeeze fan spin faster. In order for that, we have to arrange the gears to find the smallest compound gear ratio. To find the compound gear ratio, first find the gear ratio at each contact point and then multiply it together.

Proposed design: 

Gear ratio = 10/20 * 10/20 * 10/20 = 0.125

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

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

Gear ratio = 40/50 * 30/40 * 20/30 * 40*20 * 20/40 * 40/20 * 40/40 = 0.8

b. The Photo of the actual gear layout.


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
Revolution of driver gear = 1.01 * 0.8 = 0.81

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


5. Below is my learning reflection on the gears activities

This practical was eye opener and engaging as it taught me something new about gears such as gear ratio and how different gear ratio affects the speed. When I was young, I thought in order for the gear to obtain the highest speed was just to do trial and test by arranging gears in different sequences. Both activities are fun but challenging.

For the first activity, initially, we wanted to construct a compound gear train with a higher gear ratio, however we had to reconstruct the gears multiple as one of the idler gears was moving up and down when turning making its teeth not being in the other gear's teeth which cause the rest of the gear train to not rotate at all. It was very frustrating as taking out the screws was very time consuming and we had only a few hours to complete it. We had to preserve and find another solution which eventually did. This taught me to have a open mind and not to stick with only one idea which is divergent thinking which I have learn in the process operations module.

Overall, this skill is useful as it can be use to rotate parts over a length using a motor and I will definitely use it for my CA1.