During forward reduction power flows in a planetary gear set, the carrier is the output member. Additionally, maximum forward reduction is obtained if the sun gear is the input, as a smaller input gear always gives a lower output speed. Who is correct?

During forward reduction power flows in a planetary gear set, the carrier is the output member. Additionally, maximum forward reduction is obtained if the sun gear is the input, as a smaller input gear always gives a lower output speed. Who is correct?

• A. Technician A
• B. Technician B
• C. Both Technician A and Technician B
• D. Neither Technician A nor Technician B

Answer: (C)

In a planetary gear set, when you want forward reduction, locking the ring gear while driving the sun gear makes the carrier the output member. The planet gears mesh with both sun and ring; with the ring fixed, their rotation pushes the carrier to turn, but at a slower speed than the sun input. That’s why the carrier serves as the output and why its speed is reduced. The amount of reduction depends on the gear tooth counts. If the sun gear is the input and the ring gear is held, the carrier speed is a fixed fraction of the sun speed, roughly equal to the sun teeth divided by the sum of sun and ring teeth. Because this fraction decreases as the sun gear has fewer teeth, using a smaller sun gear as input yields an even smaller carrier speed for the same sun rotation. Therefore, the greatest forward reduction occurs when the sun gear is the input and the ring is held, and having a smaller sun gear as input indeed lowers the output speed. So both statements align with how forward reduction works in a planetary gear set.

In a planetary gear set, when you want forward reduction, locking the ring gear while driving the sun gear makes the carrier the output member. The planet gears mesh with both sun and ring; with the ring fixed, their rotation pushes the carrier to turn, but at a slower speed than the sun input. That’s why the carrier serves as the output and why its speed is reduced.

The amount of reduction depends on the gear tooth counts. If the sun gear is the input and the ring gear is held, the carrier speed is a fixed fraction of the sun speed, roughly equal to the sun teeth divided by the sum of sun and ring teeth. Because this fraction decreases as the sun gear has fewer teeth, using a smaller sun gear as input yields an even smaller carrier speed for the same sun rotation. Therefore, the greatest forward reduction occurs when the sun gear is the input and the ring is held, and having a smaller sun gear as input indeed lowers the output speed.

So both statements align with how forward reduction works in a planetary gear set.