# Mechanical advantage planetary gear help

1. Dec 13, 2009

### njguy

First of all, I am a newly registered user, so thanks for any help guys.

I am confused with the concept of planetary gears. Lets say there is an rpm applied to a planetary gear of 600 rpm and the gear ratio is 3:1. So the output of the planetary gear then spins 1800 rpm (600 * 3). Now my question is a bit confusing, since there is a higher gear ratio the output will be spinning faster, thus generating more torque. However the planetary gear has mechanical advantage, since the outer gears(planets) are 3 times the size of the inner gear(sun). So do they essentially cancel out? If this isn't clear please let me know. Thanks guys.

2. Dec 13, 2009

### vishal007win

are you sure output is spining faster, will produce more torque??
what exactly do you mean by "canceling out"?

3. Dec 13, 2009

### njguy

Not the output will generate more torque, but more toque will be generated against the planetary gear since the output is spinning the load faster. But will that negative torque against the gear be taken up by the mechanical advantage of the planetary gears?

Planetary gears = 3 * size of sun, since gear ratio is 3:1 thus sun spins 3* as fast

Since sun spins 3 times as fast, what would happen to the initial rpm under load?