stepper motor torque calculation

[msd]

I have following scenario attached in the file. I want to select stepper motor such that it should give sufficient torque for mentioned load. I have to select such that size of motor be minimum and torque should be sufficent...speed atleast 30rpm....

how to calculate torque for this situation so I can select stepper motor...

 

[mneary]

You want to lift 0.5kg at some undetermined point on a weightless 60cm radial? How rapid acceleration do you need? Once it is moving, speed doesn't matter, but acceleration is all-important.

Let's assume the 0.5kg is at the end of the 60cm wand. It will exert m*A gravitational force on the wand. m=0.5kg, A=about 9.8N/kg (gravity), so you need 4.9N to hold the object stationary. You'll need another 4.9N to accelerate it at the rate of 1g (my assumption.) In this case, the stepper torque will be 0.6m * 9.8N or about 6 Newton-meters. In imperial measure that's about 4.5 foot-pounds; 8638 inch-ounces.

That's a very large stepper motor.

 

[colin55]

deleted post

 

[msd]

I think we put assembly to support 60 cm radial such that the weight transfer on the support...so motor needs to apply rotating torque and may be torque required to hold the object minimize...is it sounding proper?

 

[mneary]

I don't understand your last post.

 

[msd]

I wanted to say...is it any way to reduce the gravitation force on wand such that the motor needs a torque only for rotation...the weight of object can be transfer on the assembly...
you were telling "you need 4.9N to hold the object stationary"...so my point is that is there any way to reduce that by weight transfer?

 

[mneary]

...so my point is that is there any way to reduce that by weight transfer?

You can build an opposite wand with an equal weight. That reduces the weight but doubles the mass. Choose your poison.