Calculating Stepper Motor Torque

[kdrajan]

Hi all,

This is my first experience dealing with stepper motors so lease bear with me and any stupid questions I may ask!

I have a stepper motor powering a linear stage and I want to know the maximum load it will be able to handle. I have asked the manufacturer and they want to know the speed and torque required at the motor shaft.

I know I want to be able to move at about 5 mm/s linearly but how do I go about calculating the speed and torque at the motor shaft?

Any help is appreciated. Thanks.

[hmotion]

Magic formula:
Torque = load x lead/5.65 for ballscrew or
load x lead/1.9 for Acme screw

What type and lead of screw do you have?

[kdrajan]

I have an acme screw.

How do I determine the lead?

Thanks a lot.

[hmotion]

One revolution of the screw moves it how far ahead? Or, stick your finger in one of the grooves and follow it around for 1 rev and see have far you moved (point being you just can't measure peak to peak to get the "lead" as it might be a multiple start screw.

[kdrajan]

Can I look at how far one revolution moves the stage ahead?

Or do I have to actually follow the screw for 1 rev?

[Andre' B]

A reasonably clear definition of lead and pitch.
http://www.nookindustries.com/acme/acmeglossary.cfm

[hmotion]

Whatever it take for you to figure out how far 1 rev of the screw moves things down the road. You don't need to know in microns, just is it .125, .200? Don't really care if you measure .122 or .201-get us close and we can figure it out.

[kdrajan]

Hey sorry for taking so long but I've been travelling for the past 2 weeks or so.

Anyway, the lead is 2mm. I can just plug that into your magic formula right?

[James Newton]

Originally Posted by hmotion Magic formula: Torque = load x lead/5.65 for ballscrew or load x lead/1.9 for Acme screw What type and lead of screw do you have?

I'm curious how you measure the load... aren't there many types? e.g. static, frictional, etc...

If you attach a lever of known length to the lead screw and pull with a spring scale until it turns, didn't you just measure the torque and not need the formula?

I've also really enjoyed this site, which does require registration, but then calculates everything in detail for you. They say it's only for their motors and drivers, of course, but it still produces very useful numbers in general:
http://www.galilmc.com/learning/motorsizer.php