PDA

View Full Version : Stepper motor Torque curves - what do you think of this??



Bally123
29-01-2018, 05:53 PM
Hi All

I was supplied this curve in regards to a Nema 23 3Nm (425oz-in) motor

23689

Expected it to show nearer 3Nm at low revs ??- anyone have any other comments?

Cheers

Bally

JAZZCNC
29-01-2018, 09:01 PM
They have just given you any old graph to shut you up.!

Bally123
29-01-2018, 09:58 PM
hahhaaaa.....true....

routercnc
30-01-2018, 06:52 AM
I believe they are supposed to be 3Nm holding torque (i.e. when stationary).

Once that holding torque at 0 rpm is overcome and it starts to rotate there must be a sudden drop down in torque to ~ 2Nm, and then it is down hill from there? A bit like mechanical systems where there is a high stiction force to be overcome, and then the sliding friction force is much lower?

I'm no motor expert so take the following however you like (!) - but since they give the inertia load, and the voltage applied (which is much lower than the 70-80V that the motor and driver combo will happily run on by the way) maybe it is a measured torque under those particular voltage and load conditions, rather than the higher max theoretical stall torque at any given rpm. Not much of the usual knee point on the curve, for example ? So if they are selling that motor, driver and a cheap 36V supply then perhaps that is actually what you will get torque-wise. Happy to be corrected !

Anyway perhaps a different question that you want to know is will this motor work on my machine (with a given driver etc.) - if that is what you want to know you'll get lots of real world experience and advice, so don't get too hung up on the graph. It is a popular motor (if the inductance is fairly low) and works over a wide range of DIY machines.

Desertboy
01-02-2018, 07:21 AM
Is it me or does that say pulse rate at the bottom in which case 1000 is only 5 rpm!

I'm with Jazz on this one lol.

JAZZCNC
01-02-2018, 08:34 AM
Is it me or does that say pulse rate at the bottom in which case 1000 is only 5 rpm!

I'm with Jazz on this one lol.

Yes it's pulse per sec but it's not 5rpm it's 2.5rps or 15rpm. 1000/400=2.5 x 60=15 rpm. Or high end 7000/400=17.5rps 17.5x60=1050rpm.

The thing to note is how little torque is available in the usable working range which matters most. This being when it's cutting. Which is between 300-700rpm 0r 2000pps -5000pps. So in real terms you'll have 1.2nm at best when it really matters.!

That said I don't trust these things far I could throw my machine. I'd put small wager on that this graph doesn't even belong to that motor. It really is something they put up to look good and satisfy those who feel need to see graphs.

Bally123
04-02-2018, 09:45 AM
Cheers for responses.

Spent more time with some calcs and found an excel sheet elsewhere on here which helped to confirm my thoughts.

Regards how believable the graph is...well that's always a debate with any quoted measure, even the biggest manufacturers make unachievable claims...but in general the shape or characteristic is helpful - It clarifies that holding torque is irrelevant in terms of dynamic performance and gives a clue as to usable range...

Motors have been ordered....we'll see how it goes...
Bally