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, forward reduction is achieved when the sun gear is the input and the ring gear is held stationary, causing the planets to orbit and the carrier (which holds the planets) to become the output. The speed relationship under this arrangement is ω_out = ω_in × Ns/(Ns + Nr). This means the carrier turns more slowly than the sun input, with the exact reduction depending on the tooth counts: the smaller the sun gear (Ns) relative to the ring gear (Nr), the smaller Ns/(Ns+Nr), and thus the greater the speed reduction. Therefore using the sun gear as the input gives the maximum forward reduction for a fixed ring size, since a smaller input gear yields a lower output speed. If the input or fixed member changes (for example, input at the ring or different fixed gear), the output behavior changes, but for the described forward reduction setup, the carrier is the output and the sun-as-input case indeed yields the largest reduction. So both statements are correct.