Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Analyze and calculate ratios for compound gear trains.
• Describe the function of epicyclic (planetary) gear systems.
• Perform calculations for torque, power, and efficiency.
• Identify different types of gearboxes and their applications.
• Explain the importance of lubrication in gear systems.

Lesson summary

This week, we delve deeper into advanced mechanisms and gear systems, building on the fundamental concepts we covered last week. Understanding these systems is crucial because they are the backbone of many technologies we use daily, from vehicles to manufacturing equipment. In South Africa, with its growing manufacturing and automotive industries, a solid grasp of advanced mechanisms is vital for future engineers, technicians, and designers. Imagine designing a more efficient gearbox for a taxi to reduce fuel consumption, or optimizing the conveyor belt system in a local food processing plant to increase production – these are the kinds of challenges you could tackle with this knowledge.

Lesson notes

2.1 Compound Gear Trains A compound gear train consists of more than two gears in mesh, where at least one shaft carries two or more gears that rotate together. This allows for larger gear ratios than a simple gear train using the same size gears. A compound gear train achieves significant speed reduction (or increase) and can change the direction of rotation.

Gear Ratio: The ratio of the number of teeth on the driven gear (output) to the number of teeth on the driving gear (input).

Speed Ratio (Velocity Ratio): The ratio of the input speed to the output speed. In gear trains, the speed ratio is the inverse of the gear ratio. Gear Ratio = N output / N input = T output / T input Speed Ratio = N input / N output = T output / T input Where: N = Speed (revolutions per minute or RPM) T = Number of teeth Compound Gear Train Ratio: For a compound gear train, the overall gear ratio is the product of the gear ratios of each stage. Overall Gear Ratio = (T 2 /T 1 ) (T 4 /T 3 ) * ... (T n /T n-1 )

Where: T 1 is the number of teeth on the first driving gear. T 2 is the number of teeth on the first driven gear. T 3 is the number of teeth on the second driving gear. T 4 is the number of teeth on the second driven gear, and so on.

Why it works: The intermediate gears in a compound gear train transmit the motion and modify the speed and torque. Each meshing pair of gears contributes to the overall gear ratio.