Help! Stepper stalls high speed problem?

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25 Nov 2022 20:53 #257641 by rodw
But we don't operate the motor below the corner frequency as the article says:

High initial torque at low speed does not mean efficient motor utilization. Usually power is the more important. Bias the motor’s operating point through power transmission gearing to operate the motor at its maximum power; normally just past its corner frequency.


This is why gearing is desired on a stepper motor to ensure it does not have to operate at low speed. Ideally you want to harness that low end torque above the corner frequency when the motor is accellerating. Once at constant velocity, the required torque could be 80% less.
The performance of larger motors it not so much affected by induction but by higher rotational inertia because the mass of the rotor is much larger. eg, you need more energy to turn the motor and overcome the detents.

In the OP's case, the simplest improvement he can make is to increase the motor voltage to move the torque curve upwards. Yes, he may still need to increase the size of his motor in the end, but using a 48v power supply is perfectly matchd with his motor drivers. Take the easy win first.

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25 Nov 2022 21:16 #257643 by tommylight

In the OP's case, the simplest improvement he can make is to increase the motor voltage to move the torque curve upwards. Yes, he may still need to increase the size of his motor in the end, but using a 48v power supply is perfectly matchd with his motor drivers. Take the easy win first.

[/quote]
This is the answer the OP should have gotten, thank you.

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25 Nov 2022 22:58 #257651 by Clive S

In the OP's case, the simplest improvement he can make is to increase the motor voltage to move the torque curve upwards. Yes, he may still need to increase the size of his motor in the end, but using a 48v power supply is perfectly matchd with his motor drivers. Take the easy win first.

This is the answer the OP should have gotten, thank you.


As I have said I have converted 2 Warco WM 18. A nema 17 will never work I put a nema 23 on one and the other with a 24 pullies 1.5:1 with power supply at 68V with 80v drives that was with ball screws not acme
The following user(s) said Thank You: tommylight

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25 Nov 2022 23:03 #257652 by tommylight
Sorry Clive, this have gotten out of hand as many, many times before.
And i agree, i also mentioned changing the motor to a bigger one.
Thank you.
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26 Nov 2022 00:31 #257656 by rodw

In the OP's case, the simplest improvement he can make is to increase the motor voltage to move the torque curve upwards. Yes, he may still need to increase the size of his motor in the end, but using a 48v power supply is perfectly matchd with his motor drivers. Take the easy win first.

This is the answer the OP should have gotten, thank you.

He did in my very first post on this thread...

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26 Nov 2022 00:40 #257657 by tommylight
Yes, i know, but under it is still the statement that voltage quadruples torque, that is still missing the "at higher speeds" parts.
As it stands it is not a valid statement.

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08 Dec 2022 08:40 #258882 by aleksamc
As for my cnc I use 24V because when I supply 48 then mototrs become very hot. Of course, there is losses in maximum power but I adjusted the motors for this power. For example:
- reduce maximum pulse/rate
- reduce speed.
When cnc make some process, it doesn't need speed more then 25mm/sec only when moves on G0 command.

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09 Dec 2022 00:30 #258945 by andypugh

As for my cnc I use 24V because when I supply 48 then mototrs become very hot. 

You might find that 48V with the stepper drivers set to a lower max current gives a better balance. 

Also, stepper motors are allowed to be very hot. Certainly too hot to touch is still fine. The actual limit is something like 105C, though you probably don't want to go that high. 
 

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09 Dec 2022 19:03 #259034 by mwc
I wouldn't lower current, as then you're lowering torque (current = torque for most motors).

Most steppers can be run at temps too hot to touch, some even higher.
The key point to consider, is most heat comes from the rotor, so by the time the case has warmed up, the rotor is even hotter.
Get the rotor too hot, it'll demagnetise, and your motor is only really any good for the scrap bin at point.

My guide is that provided the motor isn't getting too hot to put your hand on within 5-10 minutes, you're probably safe.
If it's too hot to hold your hand on in under 5 minutes, then you're probably pushing too much current through it.
60-80degC after an hour or more running is perfectly acceptable, unless it's somewhere exposed and somebody getting burnt on it is a real risk, in which case you probably want to overspec the motor so it can be run cooler.

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10 Dec 2022 22:27 #259146 by rodw
60-80 deg is not right. The motor should have a spec for the temperature insulation breaks down. Usually around 130 deg C
As long as you don't get that hot its fine. eg. So Andy's 105 deg is OK.
I might add this temp can be modelled as an increase over ambient but its complex.

One thing that is not well understood is the motor only requires full current when accellerating and decellerating as thats when its working. At other times, the power reuirement is low (maybe 20-30%)
This is where Lam Technology driver's boost function comes in. Linuxcnc can tell the driver when its at constant velocity and Lam can reduce the current accordingly to allow the drive to cool.

Anyway, we are are well of the track. 48V is the way forward. As Andy says you can reduce the current if it runs too hot and misses steps. It probably won't.
My motors run at 90 volts with Lam Drivers and boost.

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