In this page, I will describe definitions, relationships, how to design a better hand-squeezed fan, how my practical team carried out the gears practiacal, and my learning reflection.
DEFINITIONS
Gear module refers to the size of the gear teeth with the unit of mm.
Pitch circular diameter 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 gear module (m) equals to the pitch circular diameter (PCD) over the number of teeth.
m = PCD/No. of teeth
RELATIONSHIP
As the gear ratio increases, the torque increases for a pair of gears.
As the gear ratio increases, the output speed decreases for a pair of gears.
DESIGN BETTER FAN
3. How I can design a better hand-squeezed fan, including the sketches
To have a better hand-squeezed fan, I can increase the output speed of the fan. To do this I would need to decrease the gear ratio of the entire gear train, by having a larger input gear drive a smaller gear.
So instead of starting the gear train from the samller gear, we start from the bigger gear.
PRACTICAL
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.
LEARNING REFLECTION
5. My Learning reflection on the gears activities.
Overall this practical was quite challenging at first for the first activity. This was because we didn't know how to create the highest gear ratio, to lift up the bottle with minimal force. We thus spent too much time trying to figure out the layout for the best setup rather than creating a layout. Hence too much time was wasted and we could only try out 1 layout. But once we figured out that to get a high gear ratio, we needed a small gear to drive a large gear. I would say that took too long for my group to figure out...
So we finally calculated a total gear ratio of 26.667 from a layout we layed out, and immediately started screwing it on the board without thinking of any issues the setup brought about. Only when we tried to turn the gear to lift the bottle we realised a big issue which was the second gear was a compound gear blocking the last gear which was attached to the rope. This meant that after a few turns, the knot of the string connected to the last gear would get stuck in between the gears. Hence we could not lift the bottle by 20cm, but only by 1cm...
For the second activity it went smoothly as we had to follow the setup of the handpowered fan. This activity showed me how we can use gears in everyday handheld objects that bring us convinience in life.
Therefore, a lesson I learnt was to stop spending too much time trying to get the best results if they do not even accomplish the main goal (of lifting up the bottle by 20cm).
Of course I also learnt new terms about gears such as gear ratio, gear train, torque, compound gears, and how the gear ratio affects multiple factors.