In a planetary gear set, if the carrier is the output member, the power flow is forward reduction or underdrive.

In a planetary gear set, if the carrier is the output member, the power flow is forward reduction or underdrive.

• A. True
• B. False
• C. Only when sun is input
• D. Only when ring gear is input

Answer: (A)

In a planetary gear set, power flows from the input gear through the planet gears to the carrier. When the carrier is the output, the carrier’s rotational speed ends up slower than the driving member in the common drive configurations (for example, sun input with the ring held, or ring input with the sun held). A typical case shows the carrier speed ω_c being less than the input speed ω_in; for instance, with the sun as input and the ring fixed, ω_c = ω_s × Z_s/(Z_s + Z_r), which is clearly less than ω_s. Since the output turns in the same direction as the input but at a reduced speed, this is forward reduction, also described as underdrive. The exact ratio varies with gear tooth counts, but the qualitative behavior is the same, so the statement is true.

In a planetary gear set, power flows from the input gear through the planet gears to the carrier. When the carrier is the output, the carrier’s rotational speed ends up slower than the driving member in the common drive configurations (for example, sun input with the ring held, or ring input with the sun held). A typical case shows the carrier speed ω_c being less than the input speed ω_in; for instance, with the sun as input and the ring fixed, ω_c = ω_s × Z_s/(Z_s + Z_r), which is clearly less than ω_s. Since the output turns in the same direction as the input but at a reduced speed, this is forward reduction, also described as underdrive. The exact ratio varies with gear tooth counts, but the qualitative behavior is the same, so the statement is true.