# How to calculate torque?

1. Apr 5, 2015

### ROHIT K

dear sir ,
i am little bit confused regarding calculation of torque my question is
what is the torque required to to rotate shaft with 50000kg load with 4 rpm speed and shaft dia is 240mm.

thank you

2. Apr 5, 2015

### felmon38

If the axis is the pulley then the torque will be: 50000.9,8.0,240/2 N.m

3. Apr 5, 2015

### ROHIT K

• Please pay attention to formatting of your posts - posting in all caps is considered shouting and rude.
I AM DRIVING WITH GEAR BOX AND SHAFT DIA AT THAT POINT IS 95 MM , SO WHICH ONE SHOULD I CHOOSE IS IT LOAD APPLICATION DIA OR GEAR BOX MOUNTING DIA?

4. Apr 5, 2015

### felmon38

You must use the load diameter. If you want to know the torque at the gear box input the power at the input and at the out one must be the same. That torque will be then Ti = To.μ, where μ is the transmission relation.

5. Apr 5, 2015

### Randy Beikmann

Rohit, could you give a little more detail about your problem? Is it a belt drive system or chain drive? If either of these, the torque would be your load times the radius of the pulley or sprocket. Not sure if the "shaft diameter" you mentioned was perhaps pulley or sprocket diameter, or that of the actual shaft. In a drive system, the actual shaft diameter wouldn't matter, only the diameter of the pulley, sprocket, or gear on it.

6. Apr 6, 2015

### ROHIT K

ITS ACTUAL DIAMETER OF SHAFT AND I AM DRIVING WITH GEAR BOX AND THAT GEAR BOX IS MOUNTED ON SHAFT DIAMETER OF 95 MM.
SO WHICH ONE SHOULD I PREFER AND HOW TO CALCULATE ?

7. Apr 6, 2015

### ROHIT K

I DIDN'T GET WHAT IS THE μ . WILL U PLEASE TEL ME IN DETAIL

8. Apr 6, 2015

### Randy Beikmann

Rohit, if the system is turning at a constant speed, the diameter, mass, and length of the shaft don't matter - per Newton's first law, it takes no torque to rotate a body at a constant velocity.
What matters is the torque you are driving - the load. Now, you said the load was 50,000 kg, which is really 50,000*9.81 newtons, as a force. But that's not torque. To get torque, you need to know the radius at which the load is driven. Then T=Fr, where F is the load and r is the radius. If there is a gear box in between, you'd also have to multiply by the reduction ratio.
If this doesn't fit your actual problem well enough, you'll need to be more descriptive of it. Are you using the shaft to drive a cable that lifts a weight with a mass of 50,000 kg? I would think it through a little more based on this answer, and then state the problem very clearly. And then you'll probably solve it yourself!