Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Calculate ratios and advantage in compound and epicyclic gear trains.
• Describe the operation and uses of epicyclic gear trains.
• Explain the principles and applications of worm and worm wheel systems.
• Analyze the pros and cons of different gear types.
• Sketch and label compound, epicyclic, and worm gear systems.

Lesson summary

This week, we delve into advanced mechanisms and gear systems, building upon your foundational knowledge from previous grades. Understanding these systems is crucial because they are the backbone of many machines and technologies we rely on daily. From the gears in a tractor that helps farmers plough fields, to the complex mechanisms in mining equipment extracting resources vital to the South African economy, a solid grasp of these concepts will empower you to understand, maintain, and potentially innovate in these critical areas.

Lesson notes

2.1 Compound Gear Trains A compound gear train consists of two or more gears mounted on the same shaft. This allows for greater gear ratios and mechanical advantage compared to simple gear trains. The intermediate shaft(s) allow for the multiplication of the gear ratio achieved.

Gear Ratio (GR): The ratio of the number of teeth on the driven gear (output) to the number of teeth on the driver gear (input). GR = N_output / N_input (where N represents the number of teeth)

Velocity Ratio (VR): The inverse of the gear ratio. It represents the ratio of the input speed to the output speed. VR = N_input / N_output = Speed_input / Speed_output Mechanical Advantage (MA): The ratio of the output torque to the input torque. In an ideal system (no losses due to friction), MA = G

R. MA = Torque_output / Torque_input Calculating Gear Ratio in Compound Gear Trains: For a compound gear train with multiple gears, the overall gear ratio is the product of the individual gear ratios: GR_total = (N2 / N1) (N4 / N3) ... Where N1 is the number of teeth on the first driver gear, N2 on the first driven gear, N3 on the second driver gear, N4 on the second driven gear, and so on.