(425 oz in) @ only 4.7V and 2.8A parallel?

[Oldmanandhistoy]

Could some one with more stepper motor knowledge than me; cast their eye over these and please explain to me how they can have such a large rated holding torque (425 oz in) @ only 4.7V and 2.8A parallel?

Full spec bipolar parallel connection.

4.17V, 2.8A per phase, 6.8mH inductance per phase and 3Nm (425 oz in) holding torque.

Is there a trade off between power and speed?

Are they good value at £37.50 ($68.97 US)?

This is an Ebay item for anyone who may be interested http://cgi.ebay.co.uk/3-Nm-high-torq...QQcmdZViewItem

Does anyone know a better source for new stepper motors in the UK?

Thanks in advance for any help.

John

[jeffs555]

Yes, it is a trade off between torque and speed. You can't really know how much of a trade off it is without comparing torque curves, but 6.8mH is rather high inductance and inductance is the main thing that limits speed.

[Oldmanandhistoy]

Thanks jeffs555 for your time and the info. Is there another thread that goes into detail about inductance and if not could you give me and for the benefit of others a little more info on how this affects speed?

I have asked the seller if he has the torque curve info, if I get a reply I will post it here.

John

[pastera]

The faster you run your stepper, the faster you must change the current in the coils. The problem is that an inductor resists any change in it's current and it's dirctly proportional to inductace.
V = l*dI/dT (voltage is equal to the inductance multiplied by the change in current)

for a full step sequence, current needs to be reversed in each coil every two steps, or 100 reversals per revolution. At 60 rpm (1rps), the step period is 5ms and the current must reverse every 10mS. To keep thing quick, lets try to reverse the current in coils in 10% of the step time (0.0005s).

V = 0.0068* (2.8 - (-2.8))/(0.0005)
= 76.16 volts

That is why you want low inductance motors and this doesn't include the back EMF generated by the motor (which is not specified by most suppliers).

Aaron

[boblon]

Yes, it is a trade off between torque and speed. You can't really know how much of a trade off it is without comparing torque curves, but 6.8mH is rather high inductance and inductance is the main thing that limits speed.

Could someone please tell me what a 'decent' inductance would be for a 425oz stepper?

Thanks,
BobL.

[mcpltd]

I am 95% sure we have the torque curves for the FL60 motor with the MSD542 driver.
I can email this to you on monday.
As mantioned, inductance will choke the driver, so the lower the better, but to the way to help reduce this disadvantage is to increase the voltage to the driver.
We have quite a few customers who use this motor and they are all quite impressed with the performance.
Also they are not £37, they are £27 inc vat.

Thanks jeffs555 for your time and the info. Is there another thread that goes into detail about inductance and if not could you give me and for the benefit of others a little more info on how this affects speed?

I have asked the seller if he has the torque curve info, if I get a reply I will post it here.

John

[Oldmanandhistoy]

I have asked the seller if he has the torque curve info, if I get a reply I will post it here.

John

Shame I didn’t get an answer when I asked for the torque curves back when I started this thread.

John

[boblon]

John,
Did you finish your build? And did you use those 425 oz steppers?

I ran across this thread as I was just about convinced to buy some 425oz steppers with the same 6.8mH spec.

Got a little scared by the earlier post so figured I'd ask what a decent spec to look for in 425oz motors was.

It's a shame I didn't get an answer either.

If you used those motors, how did they work for you?

BobL.

[mcpltd]

OK, i see that this thread is quite old now.
Cant remember getting your enquiry for the torque curves, but if you are still interested, i should be able to get them for you.

Shame I didn’t get an answer when I asked for the torque curves back when I started this thread.

John

[Oldmanandhistoy]

Hi BobL,

The cnc router that I need some motors for is only now very near completion so will be looking for suitable steppers with in the next couple of weeks. I am unqualified to answer your original question and would like to know more myself.

If mcpltd is looking in I would like the torque curves for the stepper in question.

Or an idea of how much torque the stepper would have at 500-600 rpm with the MSD556 drive @ 45v, 1/8 th micro steps (1600) bipolar parallel?

Failing getting an answer to my above question or the results not being as I hope; I will be looking else where for suitable step motors and will come back to you here with what I find.

John

[boblon]

Ok John thanks.

I really am a noob and I know asking general questions like 'What motor to buy?' is almost an un-answerable question, but I would have liked to think that since it was stated that 6.8mH was a rather high spec that someone must know what a decent inductance spec for that size motor would be. Oh well.

Glad to hear your still building. Care to share what plans your going by, or is it a purely home-brewed solution? Are you going with a moving table or moving gantry design and what cutting area are you buiding to?

Good luck,
BobL.

[mcpltd]

If we have the curves they will be at half step with the msd542 only.
Do you still need them?

IK

Hi BobL,

The cnc router that I need some motors for is only now very near completion so will be looking for suitable steppers with in the next couple of weeks. I am unqualified to answer your original question and would like to know more myself.

If mcpltd is looking in I would like the torque curves for the stepper in question.

Or an idea of how much torque the stepper would have at 500-600 rpm with the MSD556 drive @ 45v, 1/8 th micro steps (1600) bipolar parallel?

Failing getting an answer to my above question or the results not being as I hope; I will be looking else where for suitable step motors and will come back to you here with what I find.

John