Gecko G540 - stepper with high Phase Inductance??

[MaxTheModder]

Hello

I am planning my CNC Project
Now I am at the point where I have to find the right steppers.
My driver will be the G540 for sure - I think it is the best drive to start off - it will operate smooth and can´t be demaged (so far I read on the net)

My machine will have dual X axis - that means i have to power 4 Steppers
All steppers will be belt reduced to half of rpm (2:1)

I think I am on the safe side when i plan with belts and pulleys - If the System is to slow for the operation I can cheaply change to another ratio (so I think)
My ballscrew pitch will be 5mm

So now I come to my real question:
I have calculated that I will need at least 1.5 Nm torque per axis but I would like to oversize them to about 2-3 Nm - so I can use them when I plan to build a bigger machine.

But the Gecko G540 is speced with 3.5A per phase MAX!
One of the 3Nm steppers I picked out has 4.2A per phase but a Phase Inductance of about 2.5mH
Another 3Nm stepper has just 3 Amp per Pahse but an Phase Inductance of 6.8mH!

So now I cant mind which of those I should take?
On the gecko drive website the claim that the supplied voltage should be the the root of the Phase Inductance multiplied by 32.

So based on that calculation the 3 AMP stepper with 3Nm (has 6.8mH Phase Inductance) would come to 83 V supplied Voltage.
But the G540 can handle only 48V - so what would happen if I connect the 3AMP stepper to the gecko with just 48V supply voltage?.

Please help me Iam very confused at the moment(even more after writing this tread ;-)

[ger21]

The higher the inductance, the lower the top speed you'll be able to attain.


Most G540 users use this motor from Keling, or one with similar specs.
KL23H2100-35-4B

Not sure how much shipping would be to Austria, if you can't find an equivalent motor locally.
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[MaxTheModder]

Thank you for your reply!
Yes I have already seen that model.
So with 3.5 A its on G540´s current maximium but it has a phase inductance of 4.1mH - which means by the calculation on the geckdrive website I would have to power the driver with 64,8V (that is over the rated maximum of 48V)
So what will suffer when powering at only 48W the driver or the torque?

[ger21]

The Inductance is 2.8mH.

If you DO use a motor with higher Inductance, then you may have a lower top speed. It really depends on how fast the machine requires the motors to spin. If they'll be spinning under 400-500rpm, you probably won't notice a difference.

[MaxTheModder]

Ok the stepper you suggested me has really only 2.8mH but I accidentally looked up for the KL23H284-35-4B - that model is claimed to be perfect for the G540 but it really has the 4.1mH so it must run undervolted.
With 2.8mH i come to 53V - I think that is ok for the G540

So please tell me what happens in these two cases (both have the G540 with 3.5A pP and 48V PSU):

1) I connect a 3Nm stepper to it with 4.2A per phase but 2.5mH
2) I connect a 3Nm stepper to it with 3.5A per phase but 4.8mH

Will suffer the torque in case 1 and the max speed in case 2??

[ger21]

With 2.8mH i come to 53V - I think that is ok for the G540

Use 48V, not 53V.

So please tell me what happens in these two cases (both have the G540 with 3.5A pP and 48V PSU):

1) I connect a 3Nm stepper to it with 4.2A per phase but 2.5mH
2) I connect a 3Nm stepper to it with 3.5A per phase but 4.8mH

Will suffer the torque in case 1 and the max speed in case 2??

Yes.

1) Holding torque will be 3.5/4.2 = 83% of rated torque.

2) Keep in mind that if you don't need the maximum possible rpm, it may not matter.

[MaxTheModder]

thanks

So in my case I would need pretty high rpm for jogging because of my 2:1 reduction.
In these torque diagramms the x is pps that are Pulses Per Second - right?
so at 200pps the stepper makes one revolution 2000pps 10 revolutions......
is that right?

My machine will need 200 Pulses to go 2,5mm so I would need 1333 pps to move my gantry 1 Meter per minute - what do you thnik is that too slow?
How many pps are normal to deal with (for jogging)?

[ger21]

Using 2:1 reduction to spin steppers 2x faster is generally a bad idea. The reason, is that steppers lose torque as rpm's increase. In some cases, a stepper spinning twice as fast can have less than half the torque. The result being, that using a gear reduction can actually decrease torque at higher rpm.

A Gecko G540 uses 1/10 microstepping, so there are 2000 steps/ motor revolution.

With direct drive, to move 1 meter, you have 20 turns of the screw, times 2000 steps per revolution, = 40000 steps/meter divide by 60 seconds, = 666.66 steps per second. So yes, with 2:1 reduction, you are correct.


What kind of machine are you building?

[MaxTheModder]

Yes I know the torque will really suffer under my 2:1 reduction.

To your example:
I really dont believe that microstepping is something to trust on (for resolution increase) In my mind microstepping is only used to make the operation smooth but you cant rely that 1/10 microstepping will increase to a 10 times higher resolution.

With 2:1 belt reduction I REALLY have 400 (full)stepps per revolution and these are REALLY accurate. It will also double to torque on the screw - that means at higher stepper rpm and a torque drop of 50% my screw still has the full power of the motor.
The only thing that will suffer is the moving speed (twice as slow)

I will be milling Aluminium on my machine so high feed speed isnt very neccary (and even not possible)

And the great thing on a belt reduced system that I can change the pulleys and belts easily to my needs - I can change them to 1:1 or 1:2 If I need higher speed (just would have to buy new belts for 30€ for 1:1)

Maybe i am talking bull**** - infact I am noob (at the moment) so please correct me if I am wrong

What reduction do you think would be best for me (without reling on microstepping)

grz MX

[ger21]

It will also double to torque on the screw - that means at higher stepper rpm and a torque drop of 50% my screw still has the full power of the motor.
The only thing that will suffer is the moving speed (twice as slow)

It's very possible the torque will drop more than 50%.
Imo, direct drive is the way to go, and cheaper than having to buy belts or pulleys.

You might want to ask Hemsworthlad, he uses his machine exclusively for aluminum.

http://www.cnczone.com/forums/diy-cn..._finished.html