How to caluclate torque for a stepper motor

[student85]

Hi actually I'm looking for a stepper motor and a driver for my Project. I have most of the specs needed but still left with an important factor which is torque.

 

I have to use a stepper motor to turn a aluminum rod which is 320mm for Length and 28mm for diameter in one direction.

 

 

I do not know the Formulae to calculate the torque with only the dimension.

 

Please kindly advice the formulae needed for the calculation.

 

 

Thanks

 

 

 

 

 

 

 

 

[Enthalpy]

Torque can't be determined from the dimensions, so don't hope for a formula.

 

What you need to estimate are friction and other losses.

Or the inertia moment in case you need a huge acceleration - probably not.

Or weight's torque in case the rotation is very eccentric and the axis not vertical.

Edited September 16, 2012 by Enthalpy

[John Cuthber]

The torque is zero unless you want to rotate the rod.

If you do then the torque depends on how fast you want to change the rotational speed of the rod.

there's also a contribution from the bearings but that might be small enough to ignore.

Edited September 16, 2012 by John Cuthber

[Joatmon]

Why do you want to rotate the rod? Is it connected to anything that has inertia or is expected to do work?

[InigoMontoya]

And about which axis are you rotating the rod?

[student85]

There will be a sensor place on top of the rod. So after scanning the area, i will rotate the rod 1 degree and continue scanning on a new area.

 

So i have to control the stepper motor to rotate the rod in either clockwise or anticlockwise direction. Therefore , i need to know the amount of torque needs

[InigoMontoya]

Not really. PID loops are positively marvelous.

[John Cuthber]

A tube will work a lot better than a rod.

Also, you need to give us some idea of how fast you want to scan things.

It is simply impossible to answer the question without that.

[student85]

Basically, i will set a timing for the scanning. After finished scanning a small area, the stepper motor will rotate the rod for about 1 degree.

 

After the rod rotated and in position, the scanning will start again. the process will keep looping, until the whole scanning cycle finished.

 

the rotate speed will not be fast. it will be the normal speed to rotate a rod.

[InigoMontoya]

Not really. PID loops are positively marvelous.

D'oh!

 

Disregard the above.

 

Apologies. Somehow I got it in my head that we were dealing with a servo motor, not a stepper.

 

it will be the normal speed to rotate a rod.

So it's OK if it takes three weeks to complete the scan? 'Seems normal enough to me.....