How Do You Calculate Torque for a Rotating Shaft with Bearings?

[ever1221]

Hello Guys,

I have a 90mm=3.543" shaft going through 2 bearings that are the same shaft weighs 10lbs bearings weigh 25lbs each hub of bearing weigh 5lbs, bearing coefficient of friction is 0.15

bearing OD: 190mm ID: 90mm

ok so I thought Torque to rotate shaft is = Moment of Inertia x angular acceleration

I want the shaft to be able to rotate at an angular speed of 15rpm so angular acc is 1.57 rad/s^2

angular acc= 1.57 rad/s^2
I= 1/2 M(r^2) --> 1/2 x 10lb x (1.77^2) = 15.7 lbm.in^2 (does this have to be converted to pound force?)

T= 15.7 x 1.57

is this right? Also how do I use coefficient of friction??

 

[Spinnor]

If there is friction then a torque is needed to keep things moving at a constant rate, the applied torque just equals the torque needed to overcome friction. You are using the formula incorrectly?

 

[Kishan Majethia]

Hello Guys,

I have a 90mm=3.543" shaft going through 2 bearings that are the same shaft weighs 10lbs bearings weigh 25lbs each hub of bearing weigh 5lbs, bearing coefficient of friction is 0.15

bearing OD: 190mm ID: 90mm

ok so I thought Torque to rotate shaft is = Moment of Inertia x angular acceleration

I want the shaft to be able to rotate at an angular speed of 15rpm so angular acc is 1.57 rad/s^2

angular acc= 1.57 rad/s^2
I= 1/2 M(r^2) --> 1/2 x 10lb x (1.77^2) = 15.7 lbm.in^2 (does this have to be converted to pound force?)

T= 15.7 x 1.57

is this right? Also how do I use coefficient of friction??

Without friction even minor torque can also rotate the shaft. So i don't suppose it will need such complicated calculations. Just force required will be equal to force required to overcome friction i suppose.

 

[OldEngr63]

I want the shaft to be able to rotate at an angular speed of 15rpm so angular acc is 1.57 rad/s^2

How do you figure this? If the shaft speed is a constant 15 rpm, then the angular acceleration is zero. Where did you get the 1.57 r/s^2 figure?

I would strongly recommend getting everything into the same units system, either US Customary or SI, but not mixed as you have it.

 

[Kishan Majethia]

How do you figure this? If the shaft speed is a constant 15 rpm, then the angular acceleration is zero. Where did you get the 1.57 r/s^2 figure?

I would strongly recommend getting everything into the same units system, either US Customary or SI, but not mixed as you have it.

And i think for getting specific speed at specific acceleration friction should be considered first because without considering friction it will always be in acceleration even with a minor amount of force.

 

[OldEngr63]

Kishan, I do not understand your statement,

because without considering friction it will always be in acceleration even with a minor amount of force.

What are you saying, please?

 

[Kishan Majethia]

Kishan, I do not understand your statement,What are you saying, please?

I want to say without considering friction and with application of minor amount of force body will always be in acceleration without considering magnitude of force except zero

 

[ever1221]

How do you figure this? If the shaft speed is a constant 15 rpm, then the angular acceleration is zero. Where did you get the 1.57 r/s^2 figure?

I would strongly recommend getting everything into the same units system, either US Customary or SI, but not mixed as you have it.

thanks guys for the replies

ok so how I got angular acc is by converting rpm to rad/s which is 1.57 rad/s and I wanted it to reach that acc within 1second so acc=angular velocity/time basically that's the motor am going to be getting, one with 15rpm but torque is what am not sure ofam having problems with units, what's the units of torque here when I use the following? I need it to be in ft lbs
I= 1/2 M(r^2) --> 1/2 x 10lb x (1.77^2) = 15.7 lbm.in^2 (does this have to be converted to pound force?)

T= 15.7 x 1.57also guys can I use this for starting toque??

http://www.engineersedge.com/friction/friction_calc_protected/shaft_journal.htm