Oilers/Plant Tenders (HHC) Civil Service Practice Exam

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What is the speed of the shaft if the crane trolley motor operates at 1200 RPM with a pinion having 24 teeth and a driven gear with 92 teeth?

  1. 120 RPM

  2. 600 RPM

  3. 300 RPM

  4. 1500 RPM

The correct answer is: 300 RPM

To determine the speed of the shaft connected to a gear system involving a pinion and a driven gear, you can utilize the gear ratio concept. The gear ratio is calculated by dividing the number of teeth on the driven gear by the number of teeth on the pinion. In this scenario, the pinion has 24 teeth and the driven gear has 92 teeth. The gear ratio can be calculated as follows: Gear Ratio = Number of Teeth on Driven Gear / Number of Teeth on Pinion = 92 / 24 = 3.8333 (approximately) Since the motor operates at 1200 RPM, the output speed of the shaft can be determined by dividing the motor speed by the gear ratio: Shaft Speed = Motor Speed / Gear Ratio = 1200 RPM / 3.8333 ≈ 312 RPM Rounding this to the nearest option provided, the most appropriate answer aligns with 300 RPM. This shows that the calculations correctly yield the output speed based on the input from the motor and the gear ratio defined by the teeth count. Hence, understanding this relationship among motor speed, gear teeth, and output speed is essential for calculating the operational speed of machinery in practical scenarios

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