Register to reply 
Determine moment of Inertia from resistance 
Share this thread: 
#1
Feb1113, 05:58 PM

P: 32

Hi Guys,
I am trying to calculate a starting torque required to move the drum at 6rpm that weights 2000kg and has 1200mm in diameter. There would be no problem to do this calc in normal circumstances as I can find a moment of inertia formula for a pipe in my book. But in this case there is a tension of 3000N acting on the rim of my drum. What will be the formula for the moment of inertia in this case? Thanks 


#2
Feb1113, 06:11 PM

Emeritus
Sci Advisor
HW Helper
Thanks
PF Gold
P: 6,301

The moment of inertia of the drum is not affected by the tension. However, overcoming this tension will figure significantly in the torque required to spin the drum.
What is this tension? Is it friction? 


#3
Feb1213, 02:23 AM

P: 32

Hi,
No it's a wire injected in the steel coil tube and I am trying to take it out. I am currently building a special machine for it and need to select the right type of motor. I was thinking of powering the drum with light duty bonfiglioli gear box housed from one side of the drum or having a sprocket arrangement with the ratio 6:1. Sprockets would significantly drive down the torque but the gearbox would suit much better for this arrangement. Yes that's right the tension will increase the torque value significatly but I don't know by how much. 


#4
Feb1213, 12:29 PM

Emeritus
Sci Advisor
HW Helper
Thanks
PF Gold
P: 6,301

Determine moment of Inertia from resistance
Well, as a first guess, I would say 3000N times the radius of the drum.



#5
Feb1513, 05:35 AM

P: 32

Thanks,
Have you got any idea how to incorporate a sprocket ratio into my torque calc? Diameter of the wheel that moves the drum has 38mm and drum has a diameter of 1200mm I incorporated the ratio into my moment of inertia of the drum. So the formula would be the following: I=Id*(38/1200)^2 Id is the moment of inertia of the drum What do you think of that? Thanks for your thoughts 


#6
Feb1513, 09:40 AM

Emeritus
Sci Advisor
HW Helper
Thanks
PF Gold
P: 6,301

The inertia of the drum is a physical property of the mass of the drum and how that mass is distributed about the axis of rotation.



#7
Feb1513, 11:03 AM

P: 32

It is but how does my pulley ratio affect that property?



#8
Feb1513, 12:21 PM

Emeritus
Sci Advisor
HW Helper
Thanks
PF Gold
P: 6,301

That's what I am trying to say: the inertia property is NOT affected by pulley ratios. The torque required to turn the drum will be affected by the pulley ratio, but not the inertia.



Register to reply 
Related Discussions  
Determine the mass moment of inertia of a quarter of an annulus  Engineering, Comp Sci, & Technology Homework  1  
Determine the moment of inertia of the wheel  Introductory Physics Homework  2  
Finding dimensions of a beam using shear, moment, and moment of Inertia  Engineering, Comp Sci, & Technology Homework  4  
Load Inertia  Mass Moment of Inertia Question  Mechanical Engineering  2  
What are moment of inertia, mass moment of inertia, and radius of gyration?  Introductory Physics Homework  1 