Gears

In week 4, we went to the lab to learn more about how gears work. Firstly, what are gears? Gears are a type of mechanism that are commonly used to perform heavy duty tasks, such as moving heavy objects.

Definitions

Gear module (m) refers to the size of teeth in millimeters. The larger the gear module, the bigger the size of the teeth. Note that gears that mesh have the same gear module.

Pitch circular diameter, PCD in short, is 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.

The number of teeth (Z) is the number of teeth that is on the gear.

The relationship between between gear module, PCD and number of teeth is m = PCD/Z

Relationship

Gear ratio = number of teeth of driven gear/number of teeth of driving gear.

The relationship between gear ratio and output speed is when the higher the gear ratio, the lower the output speed.

When gear ratio > 1, the output speed decreases.

When gear ratio < 1, the output speed increases.

As for the relationship between gear ratio and torque - when gear ratio increases, the torque increases.

When gear ratio > 1, the torque increases.

When gear ratio < 1, the torque decreases.

Proposed design for better hand-squeezed fan

To make the hand squeezed fan spin faster, we would have to increase the output speed. In order to increase the output speed, we can do so by reducing the gear ratio.

To reduce the gear ratio, we can make the driving gear bigger than the driven gear.

Practical on arrangement of gears to raise bottle

a. Calculation of the gear ratio

Gear ratio = 40/30 x 40/12 = 4.44

b. Photo of actual gear layout

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

Mass of water = 600g

Weight of water = 600g x 9.81 N/kg = 5.886 N

Diameter of winch = 6.3 cm

Radius of winch = 3.15 cm = 0.0315m

Distance moved with one revolution = 2π (0.0315m) = 0.19792 m

Distance travelled by bottle = 200 mm = 0.2m

Number of rotations required = 0.2 m/0.19792m = 1.0105 revolutions

d. Video of turning the gears to lift up the water bottle

Reflection

This practical was very engaging as there was very little guidance especially on the theoretical parts like finding the relationship between PCD, number of teeth and gear module. To do this, we had to discuss amongst ourselves and search for the answers using online resources which taught us to be more independent and become self-directed learners. While it was challenging and frustrating not having all the formulas given directly to us, it gave us a deeper understanding on how the mechanism works as we derived it ourselves.

However, we encountered a few mishaps whilst doing the activities in the practical. Initially, we were ahead of everyone as we figured out the gear ratio that allowed us to use the least force, but give us the highest output speed. We stacked the compound gears giving us a gear ratio of 27. On top of that, we also taught another group on how we achieved a high gear ratio. However, after Dr. Noel reminded us that the longest screw we could use is 2cm, we realized that the gears were stacked too high and we could no longer continue with that plan. We then wasted a lot of time by recalculating and unscrewing and re-screwing the gears on the board. The time wasted also ate into the time we had for the second activity and the quiz at the end. Furthermore, due to the lack of time, we did not plan and only realized we could have arranged the gears in a different way. If we had read properly and taken note of all the resources available to us, we would not have to rush and could have the results that would satisfy the whole group.

As for the second activity on the hand-powered fans, we were rushing from the first activity so we just quickly assembled everything without actually checking the parts.

When trying to spin the fan, it could not work and was jammed. After dismantling it, we saw that there was a broken piece. This taught us to properly check before executing a plan. Otherwise, time will be wasted when there is an error when testing it out.

Overall, this practical was fun and I got to experience how the mechanisms actually work. The group was able to work properly together despite having many setbacks.