uccnc kernel speed

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uccnc kernel speed

Postby b-rad » Sun May 05, 2019 2:18 am

Ok I know this is probably something that has been asked and I have seen some responses on the forum but still a little unclear. I am using a uc400eth with uccnc and just want to make sure that I have the kernel frequency set right. Just not sure how to calculate this as some examples I have are with mm. I am using imperial. Any way my steps per inch are 10,162.77772. This even seems high. I have built a couple of machines in the past but always left mach at 25. This is a machine that I bought that had a handheld controller that worked ok but I did not feel I had great control with it. Any way I left the yako drives with the settings it had but not sure if this should be turned down or if there is a great advantage as I do woodwork for instruments and not metal machine work.

Thanks
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Re: uccnc kernel speed

Postby Robertspark » Sun May 05, 2019 6:53 am

Please provide all your machine information.

To work out what minimum kernal speed you need you would need to know:
- Each axis steps per unit?
- Each axis maximum velocity (rapid federate)?
- Each of the stepper drives maximum step rate (100-200khz)?
- Do you have any encoders for each of the axis?
What encoder resolution are you running (pulses per revolution)?

50khz to 100khz is normally sufficient setting if you don't have encoders ... May require higher if you have encoder feedback. 100khz for cheaper drives.... 200khz for midrange drives as maximum step rate.
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
UC400eth, UC300eth, UCCNC v1.2110, Neuron Lite
UCCNC v1.2110 Macro Manual
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Re: uccnc kernel speed

Postby beefy » Sun May 05, 2019 6:57 am

Rob, we were replying at the same time. You beat me to it.

This is the wording from the manual:

Kernel frequency: The maximum frequency what the UC100 device should output can be defined
with this setting. The selectable options are 100kHz, 50kHz and 25kHz.
This parameter defines how many pulses per second the controller should produce. For example
with the 100kHz setting the maximum steps per second is 100 000 which means a 10microseconds
total time period for each pulse. With the lower frequencies the signal period is longer which makes
the setting better suite of drives built with low performance (slow) optocouplers.


If I am interpreting the above correctly, it seems the slower kernel speed will give a longer step pulse width. If your drives are capable of operating reliably on very short step pulse width, maybe you can just set the kernel speed to 100 hHz and not worry about it. Or if your maximum step pulse frequency is not very high you may be able to go for 50 Khz or even 25 Khz and have the added security/reliability of longer step pulse widths. You will need to calculate the maximum step pulses per sec by multiplying your steps/inch by the maximum inches/sec an axis will travel at. However if you have 3 axis all going at max speed at the same time I'm not sure how that affects things.

I once had a Leadshine drive that required me to set the step pulse width to 8 microseconds in Mach3. My Gecko drives would work with 2 microsecond width.

I'm not sure but my guess is that if you set the kernel frequency too low, and UCCNC cannot give the required steps/sec at max speed, an error message will pop up on screen. But like I say that's just a guess. I'd try setting the kernel speed to its lowest of 25 Khz, then using MDI to run all axis at once at rapid speed and see what happens.
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Re: uccnc kernel speed

Postby Robertspark » Sun May 05, 2019 7:55 am

Also if you are concerned about the steps pre unit, please provide:
- the leadscrew pitch for every axis
- any belt drive, or gear drive ratio for every axis
- the stepper motor steps per revolution (200 normally.... Very old drives can be different)
- the drive micro steps setting for every axis.

Eg
I have one machine I am building now that has leadscrew pitches of 4mm / turn, is belt driven 2:1 and has standard 200 steps per rev stepper motors with 10 micro steps setting

10*200*2/4 = 1000 steps per unit (mm)
1000 * 25.4 = 25,400 steps per inch
Rob
Einstein ― “If you can't explain it to a six year old, you don't understand it yourself”
...working my way through the 1000+ ways things don't work to find the one that does
UC400eth, UC300eth, UCCNC v1.2110, Neuron Lite
UCCNC v1.2110 Macro Manual
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Re: uccnc kernel speed

Postby ger21 » Sun May 05, 2019 10:54 am

I'm not sure but my guess is that if you set the kernel frequency too low, and UCCNC cannot give the required steps/sec at max speed, an error message will pop up on screen

I believe that UCCNC will just automatically reduce your maximum velocity settings if you reduce the Frequency.
Gerry
UCCNC 2017 Screenset - http://www.thecncwoodworker.com/2017.html
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Re: uccnc kernel speed

Postby ger21 » Sun May 05, 2019 11:00 am

Ok I know this is probably something that has been asked and I have seen some responses on the forum but still a little unclear. I am using a uc400eth with uccnc and just want to make sure that I have the kernel frequency set right. Just not sure how to calculate this as some examples I have are with mm. I am using imperial. Any way my steps per inch are 10,162.77772.


Generally, you just need to set it high enough to allow the maximum speed you want to achieve.
25Khz is 25,000 steps per second, or 1,500,000 steps per minute.
1,500,000/10162 = a max speed of 147ipm at 25Khz.
50Khz will allow a max speed of 294ipm.
100Khz will allow a maximum speed of 588ipm.

Note that your motors will determine the actual max speeds. Kernel Frequency just determines the maximum steps per second UCCNC can send.
Gerry
UCCNC 2017 Screenset - http://www.thecncwoodworker.com/2017.html
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Re: uccnc kernel speed

Postby b-rad » Sat May 11, 2019 5:12 am

Ok so I have it set to 50 but I am stalling some times. Not sure why, I never had this issue before I changed over from a dsp controller. any thoughs?
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Re: uccnc kernel speed

Postby ger21 » Sat May 11, 2019 10:39 am

What kind of drives do you have, and what microstep setting are they set to?

Are your velocity and acceleration settings the same as in your DSP? perhaps you have them set higher in UCCNC?

Does it stall if you set it the kernel speed to 25, or 100Khz?
Gerry
UCCNC 2017 Screenset - http://www.thecncwoodworker.com/2017.html
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Re: uccnc kernel speed

Postby b-rad » Sat May 11, 2019 5:04 pm

ger21 wrote:What kind of drives do you have, and what microstep setting are they set to?


They are yako drives ykc2405m-b3 and are set to 2000 steps.

ger21 wrote:Are your velocity and acceleration settings the same as in your DSP? perhaps you have them set higher in UCCNC?


Velocity is actually a little lower in uccnc set to 200. The dsp was 230 acceleration on uccnc is set to 10 not sure what it was on the dsp.

ger21 wrote:Does it stall if you set it the kernel speed to 25, or 100Khz?


It does stall on 100 and have not tried 25 yet as this does not match with the settings. 50 was a better fit. I can try that though
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Re: uccnc kernel speed

Postby b-rad » Mon May 13, 2019 1:05 am

So changing to 25 did not help at all still stalls. It also lowered my velocity to 140 which makes sense. Not sure what to do now
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