Noobie - Need help selecting motors

[NewCents]

I am building John Kleinbauer's "The Phoenix" and it calls for 3 50 to 120oz NEMA 23 5-Volt Stepping motors.

I found these on ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3823588356
http://www.jaegerlabs.com/motors.pdf

Would this work? I just want something cheap!

Thanks,
Chris

[sendkeys]

[NewCents]

Sorry I am having some more trouble.

Now I have to decide which one out of the 6 "NEMA 23" models best suits my application. All the 23 model types can be found on pages 6-11 here:
http://www.jaegerlabs.com/motors.pdf

Page 6 has the first "Hybrid NEMA 23" model then there are several different specs to choose from. Do I want a Drive Sequence of UNIPOLAR or BIPOLAR?

Sorry I'm really lost. I just bought some plans and as far as what the specs are of the NEMA 23 motor I'm supposed to use, it doesn't really say.

Thanks for any help,
Chris

[sendkeys]

[NewCents]

Thanks so much for the help. I truly appreciate it as this is all new to me.

It looks like there are 3 outputs:
STEP
DIR
GND

It is powered by an old computer supply

[ollopa]

OK, as I understand it NEMA 23 is a size of motor rather than a particular type. I believe it corresponds to the mounting face.

At any rate, you need a "driver" circuit (not software but hardware!) to translate the step/dir signal from the compuer into motion at the stepper motor. The cheap and common drivers (like the PIKER) are for 6-wire unipolar stepper motors.

So pick a motor/driver combination and keep them consistent--voltage, uni/bipolar, etc. If you're building by the plans or trying to keep costs down, you probably want 6-wire unipolar stepper motors about 5 volts, 50-100oz-in.

Also, the "oz" is not the weight of the motor but the holding torque in ounce-inches. In metric this is gram-centimeters (g-cm).

Hobbycnc has some nice ones that are 6v, 80oz: www . hobbycnc . com/steppers/steppers.htm

They won't make quite as much torque if you drive them with a 5v supply but they'll still run. You could also drive them with 12v and use a current-limiting resistor--they'd spin very fast but you might need to use an uncommonly large resistor. Perhaps someone with more experience doing LR current limiting will chime in here...

[arvidb]

Originally Posted by ollopa *snip* Also, the "oz" is not the weight of the motor but the holding torque in ounce-inches. In metric this is gram-centimeters (g-cm). *snip*

No, please... mass*distance (g*cm) does not give torque. Force times distance does. The metric unit for torque is Nm (Newton*meter - or Ncm if you like). g-cm, kg*cm, kg*m etc are all nonsense unit.

The misunderstanding comes from the english system using the same unit (pound, lb) for both mass and force. I have seen in some places they actually separate them: pound-mass (lbm) and pound-force (lbf). This is alot clearer (to me ). Observe that 1 lbf does not equal 1 lbm (and how could they, being units of different quantities?).

This is really weird actually: an object at earth's sea level having the mass 1 lb develops a force of gravity (weight) of 1 lb. On the moon, the same mass (1 lb) would weigh 1/5 lb. So there 1 lb 'equals' 0.2 lb. The same problems arises when you try to calculate horizontal forces here on earth.

When I see the amount of questions on this board concerning torque and force I wonder if it isn't time for the US to switch to the metric system also, to get rid of these misunderstandings...

Arvid

[ollopa]

Originally Posted by arvidb No, please... mass*distance (g*cm) does not give torque. g-cm, kg*cm, kg*m etc are all nonsense unit. Arvid

Indeed. However, due probably to imperial->metric conversions, grams are used as a measure of force about as often as pouns are used as a measure of mass. In grade school they have kids approximate their "weight" in Kg when it should be in N. From my (limited) scrounging for stepper motors it seems that several catalogs list the torque in g-cm instead of N-cm. I assumed that's what people are likely to see when shopping for steppers, so I was trying to keep consistent.

The salient point is that a "XX oz" motor should be "XX oz-in", so buy based on torque and not weight.

[arvidb]

We also sloppily say we measure our "weight" in kilos. Not so strange since all scales are marked in kg. What we do is of course that we're finding our mass by measuring our weight here at earth. It's difficult to get around this problem - we measure our weight to get our mass, and therefore say "I weigh x kg".

However, the difference between mass, force and weight is emphasized in classes, (I think high school were where they really started to make a point about this).

That companies that should know better mark their motors in "g-cm" is a bad situation. It will make things a lot more confusing for those trying to move over to the SI system. "g-cm" IS a nonsense unit and as such should never be used. Period.

(But it's nice to see that you knew what you were talking about, ollopa )

Let's say this instead: Also, the "oz" is not the weight of the motor but the holding torque in ounce-inches. In metric this is newton-metres (Nm). Gram-centimeters (g-cm) is sometimes used as an (incorrect) imperial-metric hybrid unit of torque.

That should cover it, don't you think? (Mind if I copy it and pester everybody with it until they can repeat it in their sleep? )

Arvid

[arvidb]

NewCents,

sorry for hijacking your thread. The DIR, STEP, GND are inputs to the stepper drive. This is where you connect the computer.

The drive should also have outputs where you connect your stepper. As sendkeys asked, "how many output wires to the steppers does your controller have?" This is important since it determines what kind(s) of stepper you can connect.

Arvid