Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Calculate ratios, speeds, and torque in belt drives.
• Determine appropriate chain and sprocket sizes.
• Calculate gear ratios and output speeds.
• Compare the pros and cons of belts, chains, and gears.
• Describe maintenance procedures for each system.

Lesson summary

Power transmission systems are crucial for transferring mechanical power from a source (like an engine or motor) to a driven component (like a wheel, pump, or conveyor belt). Understanding belts, chains, and gears – the primary elements of these systems – is essential for mechanical technologists. Consider the applications around you every day: the conveyor belts in supermarkets moving your groceries, the chains on bicycles allowing you to travel efficiently, and the gears in vehicles, providing the necessary torque to climb hills.

Lesson notes

2. 1.

Belts Definition: A belt drive system uses a flexible belt to transmit power between two or more rotating shafts. Power is transmitted through friction between the belt and the pulleys (also called sheaves).

Types of Belts: V-belts: Most common type due to their high power transmission capacity and good grip. Named after their V-shaped cross-section that fits into a corresponding groove in the pulley.

Flat belts: Older design, generally less efficient than V-belts but suitable for long centre distances and high speeds.

Synchronous belts (Timing belts): Have teeth that mesh with corresponding grooves in the pulleys, providing positive engagement (no slippage). Used when precise speed ratios are critical.

Ribbed Belts (Poly-V belts): Combines the flexibility of flat belts and the power transmission capability of V-belts, and is often used with serpentine belt systems (a single belt drives several components).

Key Equations for Belt Drives: Velocity Ratio (VR): The ratio of the speed of the driving pulley to the speed of the driven pulley. VR = N 1 / N 2 = D 2 / D 1 Where: N 1 = Speed of the driving pulley (e.g., RPM) N 2 = Speed of the driven pulley (e.g., RPM) D 1 = Diameter of the driving pulley (e.g., mm) D 2 = Diameter of the driven pulley (e.g., mm)

Belt Speed (V): The linear speed of the belt. Since it is the same for both pulleys (ignoring slippage): V = π D 1 N 1 = π D 2 N 2 (ensure consistent units)

Power Transmitted (P): Related to belt tension and speed P = (T 1 - T 2 ) * V Where: T 1 = Tension on the tight side of the belt (N) T 2 = Tension on the slack side of the belt (N) V = Belt speed (m/s) P = Power (Watts)