[laseruser]

Hi, how come speed information is not provided on stepper motor's product page?

Given that such information is not available, how do I compare the motors?

[peteeng]

Hello Laser - Torque vs speed graphs are provided by good suppliers & manufacturers. The results do vary depending on the quality and type of driver you use (and the driving voltage) so if your getting the motor from ebay since they do not know the driver being used its difficult to say what speed you will get. Look at stepperonline, most of the motors there have sped/torque graphs. Peter

[phomann]

Stepper motors are slow speed devices. This is due to the torque of the motor reducing with increasing speed. This occurs once the speed reaches around 400rpm. You can move this knee point to a higher rpm by increasing the stepper supply voltage.
If you have a 5mm pitch ballscrew which is directly driven by a stepper motor rotating at 400rpm, that’s 2m per minute.

Basically you need to determine how fast you need your axis to move and how much torque you need to move it then choose a suitable motor.

You need to look for a motor that has low inductance, preferably around 2mH or less. Definitely less than 5mH

Have a look at the documentation Geckodrive provides on selecting motors.

https://www.geckodrive.com/support/choosing-a-motor/


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[joeavaerage]

Hi,
the problem is that steppers lose torque the faster they go, its physics and you cant get around it.

So a stepper might go quire fast but it will have very little torque at high speed. Whats likely to happen is that you want to have the stepper go say 1000rpm, but it runs out of puff and the load
stalls it at 500rpm.

There is a figure of merit that allows you to compare steppers, and funnily enough its not the torque but is 'inductance'.
The inductance tells you how bad the torque will drop off with speed. The lower the inductance the better.

Many stepper manufacturers make high torque steppers, and high torque is good right????, but they are high inductance and they will only do a few hundred rpm before they stall. They can make them cheap
and sell them to newcomers who don't know about inductance.

Good steppers have low inductance, but that means they tend to be high current and fair to good torque and always seem to cost more!

For a 23/24 size stepper look for inductance of 1mH -2mH, 1mH preferred and reject anything over 2mH.
For a 34 size stepper look for 2mH-4mH, 2mH preferred and reject anything over 4mH.

The classic way to overcome a sluggish motor (high inductance) is to use a high voltage driver and power supply. There are plenty of good 80VDC drivers out there at good prices.
Don't settle for less and use an 80VDC supply. It will make your stepper sit up and take notice!

Craig

[laseruser]

Look at stepperonline, most of the motors there have sped/torque graphs. Peter

I had a look in the past. It is difficult to compare the performance of their motors because although such graphs are provided, they are of different scales and units. As I recall, some graphs show Pull Out Torque but others show Torque. Different products also have different frequency (PPS) and Speed scales which do not overlap.

I used to use servo motors. Manufacturers just list the recommended voltage, the torque and speed at such voltage. It is easy to compare different products. There is no need to compare the speed/torque graphs. For stepper motors, it is another story.

[joeavaerage]

Hi,
the good thing about standards is there is so many ti choose from!

Craig

[phomann]

I had a look in the past. It is difficult to compare the performance of their motors because although such graphs are provided, they are of different scales and units. As I recall, some graphs show Pull Out Torque but others show Torque. Different products also have different frequency (PPS) and Speed scales which do not overlap.

Why is speed important to you?
What speed are you after?
Cheers
Peter


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[laseruser]

From 0.01 mm/sec to reasonable normal moving speed. Hard to describe what that is.

[peteeng]

Hi Laser - If its hard to describe then you can't specify the system. You are quoting a velocity. Motors spin so you will need a gearbox, ballscrew, belt drive, R&P ???? if you can't figure out the change of units then you need to read up on that.... All steppers are speced as their pull out or zero speed torque. As a general statement that torque linearly decreases to about zero at 1000rpm... So you have max torque (specified torque at zero speed and zero torque at 1000rpm) servos are constant torque devices so the quoted torque is available within the speed range of the motor. Plus servos can run at 3000rpm and faster... Peter

[phomann]

From 0.01 mm/sec to reasonable normal moving speed. Hard to describe what that is.

Do you know what drive train you are planning to use, and what resolution you need?

If so you can calculate what speed you need. Chances are the stepper speed won’t be as issue.

Your question is a bit like buying a bulldozer and asking the salesman what is the top speed. It’s not a parameter to 99% of use cases.

If it’s an issue then maybe you need a servo instead of a stepper.

You need to start with what is being moved, the spindle or whatever, determine the weight of it, work out what resolution and speed you need. Then based on the drive train you plan to use, that will determine the speed of the motor. Then you can decide what motor size and type you need.

I design for a max stepper speeds of around 600-800 rpm, but that’s not cutting anything. On my mill with 5mm pitch ballscrews, when cutting at say 500mm/min the stepper motor is turning at 100rpm. With rapids at 2.5m/min they are turning at 500rpm.

Cheers

Peter.


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[laseruser]

Hi,
For a 23/24 size stepper look for inductance of 1mH -2mH, 1mH preferred and reject anything over 2mH.
For a 34 size stepper look for 2mH-4mH, 2mH preferred and reject anything over 4mH.
Craig

How about NEMA17 motors? Is inductance of about 3mH acceptable?

[joeavaerage]

Hi,
no not really, or if you do accept them they'll be slow. Look for 1mH or less.

Craig

[peteeng]

Hi Laser - You need to specify your speed and torque requirements for people to accurately comment. You need to look at the speed torque graphs and check it does what you need it to do and again, it comes down to the driver quality and the driving voltage to what that motor can achieve. 3mH is an average sort of spec for an economy motor... I've run 3mH motors well over 2000rpm but they have no torque. Peter