Load Inertia Question

[mselak500]

I'm looking for some help to verify a calcualtion that was made by a previous employee.

The calcualtion was for load inetria (reflected to the motor). The motor will be driving (3) rollers at a gear ratio of 3.5:1 (motor turns 3.5 revolutions for every 1 revolution of the rolls).

I have a program that caluclates the mass moment of inertia for the rolls, and was able to verify this calucations with formulas that I found on the internet. The total inertia for all (3) rolls is 67,155 lbm-in^2. I converted this to 19.65 kg-m^2. If I divide this by the gear ratio of 3.5, I come up with 5.6 kg-m^2.

The previous employee came up with 2.4 kg-m^2.

Can someone help to tell me what I'm doing wrong.

Thanks,

 

[BobM3]

For reflected inertia you would divide by the square of the gear ratio. That gives 19.65/(3.5*3.5) = 1.6. Maybe the previous employee also added the motor's own inertia to come up with the 2.4 number.

 

[MechEng2005]

Or a "safety factor" of 1.5