# Gear Train horsepower calculation

## Main Question or Discussion Point

I am designing a gear train for my basic mechanisms class that consists of three shafts. The input horsepower is 10 and rpm is 1750. I calculated the torque of the first shaft to be 360 but I am not sure if the horsepower stays the same throughout the whole train or not. The first shaft has a 14t gear meshing witha 40t gear on shaft two. Shaft two then has a 22t gear meshing with a 48t gear on shaft three for an output rpm of 281. In order to calculate the torque and force per tooth of each gear do I just use the input horsepower? Thanks in advance for any help.

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SteamKing
Staff Emeritus
Homework Helper
The torque will be multiplied (or reduced) depending on the ratio of gears between the input and output. Except for minor frictional losses in the geartrain, power in should be approx. the same as power out. (Well-designed gear boxes usually have 2-3% loss).

For example, the first gear ratio is 40:14 or a ratio of 2.857 : 1. The input speed of 1750 rpm is slowed to 1750/2.857 = 612.5 RPM, and the input torque is multiplied to become 360*2.857 = 1028.6 in-lb.

So is the 1028.6 in-lb the torque for the entire second shaft (the 40t and 22t gears) or the torque for the 40t gear alone? Thank you!

SteamKing
Staff Emeritus