Stepper stalls high speed

[Petro1head]

First post and wish i had found this forum a few months ago

They say stepper motor suppliers love newbies

I have a Warco wm18 mill and have added a power z axis stepper but it stalls at high speed

This is the driver i am using - https://www.omc-stepperonline.com/di...or-dm542t.html

This is the stepper motor - https://www.ebay.co.uk/itm/Nema-23-S...53.m2749.l2649

This is the power supply - https://www.omc-stepperonline.com/po...ent-a%5B6.5%5D

I have set the driver to 4.2a and i think, can't remember without opening enclosure, to 1600 steps/rev

It works quite well but tends to stall at max speed especially raising the head. For info the head does have a gas strut helper

so where have i gone wrong?

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[Petro1head]

Added subscription

[joeavaerage]

Hi,
that stepper has 3,8mH of inductance and it will lose torque at speed badly.

With a 23 size stepper look for a unit with 1mH -2mH, 1mH preferred.

To counteract inductance use the highest voltage power supply your drivers can handle. Most of the Gecko drivers, the gold standard
are 80V capable so use 80V. Leadshine AM822 are also 80V and somewhat cheaper.

Craig

[joeavaerage]

Hi,
just increasing the voltage of your power supply might help, or at least be enough. The drivers a 60V capable so us 60V.
24V wouldn't 'pull the skin off a rice pudding'.

Craig

[Petro1head]

Hi,
just increasing the voltage of your power supply might help, or at least be enough. The drivers a 60V capable so us 60V.
24V wouldn't 'pull the skin off a rice pudding'.

Craig

thanks for the replies, i did wonder about the voltage

I posted an incorrect link to the motor and driver. Now updated, max power 50v so will try a 48v power supply

[joeavaerage]

Hi,
at 5mH it is not surprising that the stepper stalls at speed.

Inductance is a measure of how 'magnetic' the motor windings are. When voltage is applied to a coil the current does not flow instantly but builds up
over a short period of time. Inductance describes mathematically the physical parameter that determines how long it takes for the current to build up.

The torque of a stepper is max when the current is at rated level, in your case 3.5A will produce about 3Nm torque. Each time the stepper is required to rotate
or 'step' the current must build up to this level so the armature can rotate the load. The step must complete before another step comes along and the
process repeats. All these 'steps' take time.

Your stepper with 5mH inductance is likely to have as little as 10% of its rated torque at 1000rpm, and as a consequence will never get to 1000 rpm before it
stalls. Another stepper, lets say smaller, say 2Nm but only 1mH inductance will have about 45-50% of its rated torque at 1000rpm ie 1Nm@1000rpm
cf 0.3Nm@1000rpm with your current stepper.

This illustrates the point that sometimes a stepper with lower torque but also very low inductance will outperform a stepper with high torque but also
high inductance.

Stepper mabufacturers know that first time buyers always look for the highest torque for a given size motor without considering inductance.
So they make motors with high torque but also commensurately high inductance so they can make a sale. Now that you know you might chose
another stepper, the same physical size but lower torque but more importantly much lower inductance.

Craig

[joeavaerage]

Hi,
I thought I'd add a few of picutres that might illustrate the difference.

In truth it is not JUST the inductance that matters but also the resistance. The product of the two is called the time constant, and is an important number
or figure of merit and results from solving the classic first order differential equation beloved of physicists and engineers.

The three pics are a representative circuit of one winding of a stepper. One pic has a winding resistance of 1.2 Ohm and an inductance of 5mH,
the specs for your steppers. The voltage source is a pulse generator that produces a 4.5V pulse starting at t=1ms. Note how the current
builds up slowly, only getting near to 3.5A after 15ms when the pulse turns off.

The second pic is with 1mH inductance but the same resistance. Not how much faster the current builds up. About 3ms to get to 3.5A

The third pic is now with even lower resistance. If you are trying to make a low inductance stepper you use fewer turns on larger diameter wire that
results in low inductance but also low resistance. This combination is a realistic representation of such a stepper. Resistance of 0.5 Ohm and
inductance of 1mH. Note that for the same 4.5V pulse the eventual current would be 9A! That is too much for your stepper so the driver limits
the current to 3.5A, the horizontal line I've drawn in green. Note how quickly the current builds up to 3.5A though, scarcely 1 ms to 3.5A.
This stepper could run very VERY much more quickly than yours.

Craig

[Petro1head]

Thanks Craig, my head is spinning now

Apologies, this is the actual motor i am using - https://www.ebay.co.uk/itm/Nema-23-S...53.m2749.l2649

What would be the result if i use 48v instead of the current 24v?

Also, not sure if this is relevant, i use one of these to control the speed - https://www.ebay.co.uk/itm/Stepper-M...53.m2749.l2649

[joeavaerage]

Hi,
increasing the voltage will always help any given stepper go faster before it stalls, so it will help. Will it help enough? I don't know.

The stepper you linked to has 3.8mH and 0.9 Ohm windings. By no means the worst I've seen but by no means the best either.
May I suggest upping the voltage to as high as your drivers will tolerate and try it. If they still stall then you will either have to accept
slower G0's OR replace the steppers with better ones.

What is that speed control unit for? Is that the driver for the steppers? Does it have microstepping? What about the drivers that you linked to
in your first post...do you have those or not?

Craig

[Petro1head]

Hi,
increasing the voltage will always help any given stepper go faster before it stalls, so it will help. Will it help enough? I don't know.

The stepper you linked to has 3.8mH and 0.9 Ohm windings. By no means the worst I've seen but by no means the best either.
May I suggest upping the voltage to as high as your drivers will tolerate and try it. If they still stall then you will either have to accept
slower G0's OR replace the steppers with better ones.

What is that speed control unit for? Is that the driver for the steppers? Does it have microstepping? What about the drivers that you linked to
in your first post...do you have those or not?

Craig

Thanks Craig

Well the motor I linked to is better than the other, step in the right direction.

I have ordered a 48v power supply

The speed control usit is as well as the stepper driver. Got the idea from a YouTube vid where a guy converted his milling machine -

[joeavaerage]

Hi,
you need a proper stepper driver, something like an AM822 and don't bother with a 48V supply, get at least 72V or better 80V.
If you want your steppers to perform you MUST provide the BEST POSSIBLE drive.

https://www.ebay.com/itm/Leadshine-A...b0f56543c8983a

Craig

[routalot]

I'm guessing from the username and the Warco machine that the OP is UK based.The power supply is 150 watts and thus a touch on the modest side.One further question-what pitch is the leadscrew ?

[Petro1head]

Hi,
you need a proper stepper driver, something like an AM822 and don't bother with a 48V supply, get at least 72V or better 80V.
If you want your steppers to perform you MUST provide the BEST POSSIBLE drive.

[Craig

However the spec of the driver says max 50v

[Petro1head]

I'm guessing from the username and the Warco machine that the OP is UK based.The power supply is 150 watts and thus a touch on the modest side.One further question-what pitch is the leadscrew ?

Yeh, UK based, how do I add Location under my username?

I have ordered a 48V 240w power supply to try

I believe the leadscrew pitch is 4mm

[routalot]

My totally unscientific notion is that if it was stalling once in a while with a 150W power supply,the 60% power increase should make it a thing of the past.

[Petro1head]

Fingers crossed

[joeavaerage]

Hi,

However the spec of the driver says max 50v

What drivers do you have? I've asked the question but still don't know.

My totally unscientific notion is that if it was stalling once in a while with a 150W power supply,the 60% power increase should make it a thing of the past.

Wrong. Steppers are CONSTANT CURRENT devices, the only advantage of a higher voltage is that it might run a bit faster.
If the stepper is 3.5A and the driver (whatever it is!!!) is set accordingly then if the voltage of the supply is 24V the stepper will take 3.5A.
If the voltage of the supply is 48V the stepper will take 3.5A.

In both cases they will produce the SAME HOLDING TORQUE.

The higher voltage supply will 'push' a little harder and consequently the current will get up to 3.5A that little bit faster....so hopefully it will
'step' a little faster ie turn that bit faster without stalling. That's all a higher voltage supply and/or driver will get you. The only other way is to get
low inductance steppers as I have recommended.

Craig

[Petro1head]

Hi

What drivers do you have?

Craig

The link is is my first post, here it is https://www.omc-stepperonline.com/di...ytIlkfUVqRFhug

If its no better after i get the new power supply, which is what your saying, then will start again and before doing so will seek you advice

Thanks again Craig

Ps how does the steps per rev affect things if at all

[joeavaerage]

Hi,
OK, you have a 50V drive, a 48V power supply is indicated. It may be enough, I would guess that you will get about 25% extra torque at G0 speed
and maybe that is enough to prevent a stall.

Craig

[joeavaerage]

Hi,

Ps how does the steps per rev affect things if at all

In terms of stalling at speed steps per rev, also called microstepping, has little or no effect.

There is one proviso however, if you set the steps per rev too high the controller will not be able to supply the number of
pulses in a given time and therefore the motion will not exceed some erratic maximum..

It is seductive to beleive that increasing microsteps increases resolution, beyond 400 pulses per rev that is however, fallacious.
What microstepping does do is smooth the motion and greatly reduces the propensity to mid band oscillation to which all steppers
are subject to.

I would recommend 8 microstep per fullstep or 1600 pulses per rev. You get good smoothing WITHOUT demanding a high frequency step
rate and thereby stress or exceed your controllers ability.

Craig