How strong are 100oz steppers?

[mvaughn]

I'm curious what 100oz steppers equate to in foot-lbs or inch-lbs. Is it a measurement of torque even?

Someone please shed some light on this?

[cbcnc]

Mvaughn,

I tested some of my motors using this technique: "How To Test Stepper Performance" .
The rating of a motor is supposed to be in oz./in. or ft./lbs. I have also seen them rated in the metric system.
So, a 100 oz. motor will hold 100 oz. hanging off a 1" arm. Or 10 oz off of a 10" arm. Or 8.33 lbs / .0833 ft.
The real specs though are in the torque curve. That is a graph that shows, that at a particular voltage, how much torque the motor puts out as you vary the speed.
Here are some torque curves for an Oriental Motor PK266-2A

Chris

[mvaughn]

In laymans terms 100oz steppers are 100 oz/inch or 6.25 lbs/inch?

[cbcnc]

Mark,

Yes you are right. My math was wrong.

Chris

[arvidb]

I'm curious what 100oz steppers equate to in foot-lbs or inch-lbs. Is it a measurement of torque even?

Someone please shed some light on this?

No, 100 oz is not a measurement of torque, it's a measurement of mass. However, it is commonly (IMO incorrectly) used as a shorthand for oz*in (also often and IMO incorrectly written as oz-in). And this is a measurement of torque, if you look on the "oz" as a measurement of force (I guess it should really be ozf*in or ounce-force-inch). The metric unit of torque is the newton meter (written Nm), i.e. a product of force (N) and distance (m).

The rating of a motor is supposed to be in oz./in. or ft./lbs. I have also seen them rated in the metric system.
So, a 100 oz. motor will hold 100 oz. hanging off a 1" arm. Or 10 oz off of a 10" arm.

This is wrong. The torque rating of a motor is supposed to be in ozf*in, lbf*in, lbf*ft, etc (here the f's indicate force as opposed to mass), or in the metric system Nm. Sometimes a hybrid between the metric and imperial system is used: the nonsense unit kg*cm. However, mass times distance (as in kg*cm) makes no sense; it certainly is not a unit of torque.

100 ozf*in divided by 1 in gives 100 oz of force, and 100 ozf*in divided by 10 in gives 10 oz of force, as you wrote.


For more information about this, see the CNCMechanics document in the FAQ section:
What motor, screw and gearing should I choose?

Arvid

[sol]

100 oz.in. is just over ½ ft.lb....

For comparison:
A rechargeable screwdriver is around 640 oz in, they are advertized as 40 in.lb which is 3.34 ft lbs. That is easily overpowered by the user.
A basic 8 inch long wrench will allow you to strip threads rated at 20 ft.lbs or 3840 oz.in.(too ) easily.

[ESjaavik]

I'll just mention the benefits of metric here.
On second thought, no I will not. All of you already did that better than I thought possible.

[mvaughn]

I don't doubt that metric is much easier and better. However, when you've been taught to think in imperial all your life it helps to put things in those terms sometimes.

[arvidb]

LOL @ Einar

When you think about it, it's incredible that NASA managed to put a man on the moon using the imperial system! It just makes my admiration for those people so much greater!

(I'm also brought up on the metric system, but have been forced to use the imperial system from time to time, and that has made me understand how clever the metric system really is.)

Arvid

[mvaughn]

It's more simplistic than clever. A base10 numbering system makes the most sense to us...

who knows, if we had 12 fingers instead of 10 the imperial system would be king!

[arvidb]

I think it's also clever. There is one unit for every quantity to be measured, and all units are defined to fit together very nicely.
And the prefixes makes it easy to express smaller/bigger quantities, while still making it possible to use exactly the same equations. (As opposed to the imperial system, where a change from f.ex. inches to feet requires a change of conversion factors.)

Arvid

[mvaughn]

Good point!