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Author Topic: How to know how much khz to set in mach3  (Read 9304 times)

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How to know how much khz to set in mach3
« on: March 16, 2014, 03:16:26 AM »
First of all I'm new here and this is my first post. greetings to everyone. :)
I'm been reading a lot here about everything, but still have some questions.

My setup:

PC:

Dualcore 2600
2GB ram
500gb HD
graphic card ATI 256mb
Windows 7  32bit


MACH3 setup

Version 2,68  (With newer version I have problems wirth rapids when gcode is loaded)
V 2.68 works perfectly, but in version 2,68 the driver test in mach 3 folder is set to 25 khz and I cant change it to see how it performs under higher pulse rates.
When I change the khz in mach3 under pins and port to 100 khz and then goes to diagnostic tab under pulse freqency it stys at 94000 + - 50 khz.

I'm a metric user so under config tab a have:

select native units:  mm

ports and pins: have set to 100 khz
(the other parameters are ok everything works like it should)

Motor tuning:

steps per: 200       velocity: 1500    acceleration: 100

same is for y,z and a axis

On the x axis I have two motors so I slaved A axis.

This is the setup:

I have nema 34 1600 oz 1,8 200 per rotation
My ball bearing actuator has 5mm per rotation
Driver: DM 860A set on 1000 (I tried every micro stepping mode but with more micro step per rotation I get lower speeds and more pulses are needed for faster rotation)

every driver has its own power supply on 60v 7,8 amp

And here is my problem.
I want to go faster but  when I set the  velocity to 3000 or 4000 the motor turns ok (I tried to stop it but they are to strong) but when 2 or more axis are engaged at same time i get missing steps.
Can someone calculate theoretical speed that I can get from my setup?
Is it possible that with 4 axis one is slave at 3000 my pulse rate is to slow even in 100 khz mode?

Or do I have to buy smooth stepper to go faster?

Thanks a lot.

Regards
mike




Offline stirling

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Re: How to know how much khz to set in mach3
« Reply #1 on: March 16, 2014, 04:56:13 AM »
kernel speed required = (steps per unit * velocity in units per minute) / 60. Choose the lowest kernel above this figure. Choosing anything higher is a) pointless and b) likely to cause problems.

Depending on what type of machine you have, you may well be another victim of the bigger is better mistake. Large stepper motors are NOT good for speed. They're better at shifting large loads slowly. Smaller motors may well be the way to go if you want speed.

Microstepping "typically" should be set to 10.
Re: How to know how much khz to set in mach3
« Reply #2 on: March 16, 2014, 06:11:22 AM »
Thank you for your fast replay  :)

So I have:

(200*1500)/60 = 5000khz

and if I want to go 3000 velocity

(200*3000)/60 = 10000khz

So 25000 khz is more than enough for my spped.

Why do my motors  lose steps when running at 3000 velocity?

And not to mention they are not connected to anything yet.

Offline Hood

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Re: How to know how much khz to set in mach3
« Reply #3 on: March 16, 2014, 06:42:29 AM »
Why do my motors  lose steps when running at 3000 velocity?

And not to mention they are not connected to anything yet.


Steppers have all their torque at low RPMs, increase the RPM and torque falls of a cliff, also as Ian has mentioned, bigger is not always better, just depends on the machine and the way things are geared as to which mototr would work the best. I am a servo man, torque is more or less constant no matter the RPM and huge overhead of peak torque for short periods :) But steppers have their place, they work well as long as you work within their capabilities.

Hood

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Re: How to know how much khz to set in mach3
« Reply #4 on: March 16, 2014, 06:49:22 AM »
Just read your OP again and although you dont mention the machine type/setup/weight etc it kind of sounds like it may be a router. It seems like you may be running direct coupled and if so 3m/min would be about 600rpm which is likely top end for a big stepper, might be worth your while gearing 1:2 if possible, you may still have plenty of torque with the big motors and you will get twice the Velocity for a given motors RPM.
Hood

Offline stirling

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Re: How to know how much khz to set in mach3
« Reply #5 on: March 16, 2014, 07:54:29 AM »
when I set the  velocity to 3000 or 4000 the motor turns ok (I tried to stop it but they are to strong) but when 2 or more axis are engaged at same time i get missing steps.

This is curious. When you say "engaged" do you mean enabled or moving?

And not to mention they are not connected to anything yet.

Do you mean they're not bolted to anything i.e. sitting on a bench? If so then this can be misleading. Resonance is more likely to occur on an unmounted motor. Which also takes me back to your lack of microstepping. This is also likely to cause resonance problems.

Out of interest - do you have a link to the data sheets for your motors and drivers?
Re: How to know how much khz to set in mach3
« Reply #6 on: March 16, 2014, 08:00:00 AM »
Sorry
Yes it is a router and yes it is direct coupled

I have also smaller nema 23 400 oz and they behave the same.

Im currently running at 1600 velocity and when I increase to 3000 then it starts to miss steps.

Weight ?

It is a small router.  1000mm x 500mm. z axis 50mm

I know that the steppers looses torque with increasing speed but the motors  are not connected to anything, they are running freely at the moment.
Re: How to know how much khz to set in mach3
« Reply #7 on: March 16, 2014, 08:13:32 AM »
when I set the  velocity to 3000 or 4000 the motor turns ok (I tried to stop it but they are to strong) but when 2 or more axis are engaged at same time i get missing steps.

This is curious. When you say "engaged" do you mean enabled or moving?

And not to mention they are not connected to anything yet.

Do you mean they're not bolted to anything i.e. sitting on a bench? If so then this can be misleading. Resonance is more likely to occur on an unmounted motor. Which also takes me back to your lack of microstepping. This is also likely to cause resonance problems.

Out of interest - do you have a link to the data sheets for your motors and drivers?

Yes, when I mean engaged I mean moving two or more axis at the same time.

Yes. the motors are not bolted. It may be a problem. I didn't think about it.
I am currently running it on 60v.

Attahced I am sending you the datasheet for the driver.
Here is the link for the motor datasheet:
http://sine.ni.com/ds/app/doc/p/id/ds-311/lang/hr



Offline ger21

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Re: How to know how much khz to set in mach3
« Reply #8 on: March 16, 2014, 08:19:46 AM »
Another thing to try is this.

Go into the PC Bios, and disable C1E or EIST if you have them. This allows Mach3 to run much better on some multi core PC's.

However, most 1600oz steppers are very slow. Ebay is flooded with them, and I see this all the time. People buy them, thinking bigger is better. In actual use, a 450oz Nema 34 will often run a router at 5x faster than a 1600oz motor.
Gerry

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Offline stirling

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Re: How to know how much khz to set in mach3
« Reply #9 on: March 16, 2014, 08:41:33 AM »
There's no 1600 oz/in motor on that page. Anyway - IMHO you're making a rod for your back trying to use those motors on a small router - personally I'd switch to your 23s. You can't just say they behave the same - they're completely different motors and will need driving differently. Do you have a part number or spec sheet for them?

FWIW I use 3Nm 23s on my router which is just a little bigger than yours and I can get 15m/min rapids and 0.5G accel.