# Compound gear train problem (WHY IS IT SO HARD )

Compound gear train problem (WHY IS IT SO HARD!!!!!)

## Homework Statement

http://img5.imageshack.us/img5/1663/problemw.jpg [Broken]

I need to calculate the angular acceleration of the fan at 2600 RPM (motor speed) depicted by figure 4.

## Homework Equations

Sum(torques with respect to input) = (torque applied by motor)-(torque load from output shaft with respect to gear ratios)

THEN

Sum(torques with respect to input) =( sum of intertia's with respect to input and gear ratio's) x (angular acceleration of input shaft)

## The Attempt at a Solution

Now my problem is that there are no moments of inertia given for the gears in the system. I'm assuming the torque load on the output shaft caused by the fan is a form of torque lost due to air resistance of the fan. Thus the faster the fan the higher the torque lost.

Basic formulation I'm using is:

Sum(torques with respect to input) = (torque applied by motor)-(torque load from output shaft with respect to gear ratios)

THEN

Sum(torques with respect to input) =( sum of intertia's with respect to input and gear ratio's) x (angular acceleration of input shaft)

Then I can use the (angular acceleration of input shaft) to find the angular acceleration of the output shaft using gear ratios.

My main problem is that I dont have all the intertia's of the gear system! So do I simply ignore the other moment of inertia's or is there a correct way of calculating them!!!

A little advice / help please!!!

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## Answers and Replies

No need to calculate the moment of intertia of gears.

It is small compare to the work loss from the other side.

If you really need to calculate that.

We know the gears sizes d=N/P (N:number of teeth ,P:diametial pitch, d:diateter)
The same P is required to compose the gears.

We known the center distance c = (d59+d21)/2 =(d55+d21)/2

P59=P21, P55=P21 => d59:d21 = 59:21

Then we can calculate the diameter of gears by finding the hand book.

There is a fixed specification by product.

Then see what material you use.

Having say so ,you DO NOT need to calculate the intertial .lol