If the carrier is the held component in a planetary gear set and the sun gear is the input member, the result is a reverse overdrive.

If the carrier is the held component in a planetary gear set and the sun gear is the input member, the result is a reverse overdrive.

• A. True
• B. False
• C. True only if ring gear is input
• D. True only if carrier is output

Answer: (B)

When the carrier is held and the sun gear is fed with input, the planet gears are forced to move in a way that makes the ring gear rotate in the opposite direction to the sun. The speed of that ring gear, however, is determined by the gear tooth counts. In a typical planetary set where the ring has more teeth than the sun, the ring’s speed in magnitude is less than the sun’s input speed, producing a reverse underdrive rather than a reverse overdrive. Overdrive would mean the output turns faster than the input, which isn’t the usual result under this condition (and would only occur in uncommon tooth-count arrangements). So the statement claiming reverse overdrive is not generally correct.

When the carrier is held and the sun gear is fed with input, the planet gears are forced to move in a way that makes the ring gear rotate in the opposite direction to the sun. The speed of that ring gear, however, is determined by the gear tooth counts. In a typical planetary set where the ring has more teeth than the sun, the ring’s speed in magnitude is less than the sun’s input speed, producing a reverse underdrive rather than a reverse overdrive. Overdrive would mean the output turns faster than the input, which isn’t the usual result under this condition (and would only occur in uncommon tooth-count arrangements). So the statement claiming reverse overdrive is not generally correct.