UCCNC Max Speed?

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UCCNC Max Speed?

Postby drxlcarfreak » Fri Nov 09, 2018 4:44 pm

I just got my Teknic Clearpath motors up and running last night. It looks like I reached a limitation of the software. When I had the resolution at 3200 steps/rev which equates to ~3259 steps/inch on my machine, I tried upping the jogging velocity to 1000 IPM, it let me apply fine, but when I jogged, it reached a maximum of 874.4 IPM, which is 47,500 steps/second. When I lowered the resolution to 1600 steps/rev, I was then able to up the jogging speed until the servo reached voltage saturation. Granted, I don't need to go that fast, I just wanted to see how quickly I could get them to go on my machine, but I am curious just to understand how the software works better, is there a set limitation of steps/second per axis?
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Re: UCCNC Max Speed?

Postby ger21 » Fri Nov 09, 2018 5:26 pm

The Kernel Frequency setting. Your options depend on which motion controller you are using.

Do the Clearpath servos have electronic gearing? If you are maxing out the pulse frequency, electronic gearing will let you go faster.
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Re: UCCNC Max Speed?

Postby drxlcarfreak » Fri Nov 09, 2018 5:50 pm

Ahh, that makes sense. I think I dropped it to 50k or 100k before to try and diagnose issues with my previous stepper setup. I am using the UC300ETH, so I shouldn't have an issue upping it to 300khz, right?

I think so. I have options to set the servo to 6400 steps/rev which is 1:1 down to 800 steps/rev which is 8:1. Upping the electronic gearing basically reduces the amount of counts per rev, but also the resolution, right?
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Re: UCCNC Max Speed?

Postby ger21 » Fri Nov 09, 2018 6:55 pm

Since there is no 300Khz setting, yes, you may have trouble. Try 200 or 400Khz. :D
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Re: UCCNC Max Speed?

Postby drxlcarfreak » Mon Nov 12, 2018 3:49 pm

Haha whoops! That worked! Awesome, thank you! I am now cruising at 3259 steps/inch at 1300IPM. Once I got them tuned correctly, these new motors are awesome! Granted it may be due to the new nema 34 pinions I put on, but I actually had to turn off my backlash compensation. There is no measurable (at least to me) backlash at all.

Dumb question, is there any reason not to max out the kernel frequency setting?
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Re: UCCNC Max Speed?

Postby Robertspark » Mon Nov 12, 2018 4:47 pm

drxlcarfreak wrote:Dumb question, is there any reason not to max out the kernel frequency setting?


none really if you have fast servos and steppers that can accept high speed inputs.

It normally comes down to the optoisolators within the drives (and breakout boards if you have or use one).

Extract of my leadshine AM882 drives below (its what I had to hand)..... whatever you drives you use will have something similar
Attachments
2018-11-12 16_43_59-AM882m_20100221.doc.png
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 v1.2106, Neuron Lite
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Re: UCCNC Max Speed?

Postby cncdrive » Mon Nov 12, 2018 5:24 pm

Low end drives with cheap slow optocouplers can't handle 400kHz, not even 200kHz and often not even 100kHz.
Usually chinese drive manufacturers put slow optocouplers into the drives, because they are cheap and it does matter if they put a $0.5 optocoupler or a $0.05 optocoupler when they make 100 000 drives a year. Then that is a big difference in cost and in their profit.
And in most drives it does not matter much if you use medium to very high resolution and stepper motors can't rotate very fast, because on high speed they loose torque and so using slow optocouplers is kind of understandable.

Mostly servo drives can handle 400kHz, because servos can have high encoder resolution and therefor using fast optocouplers is an advantage or maybe I can say it is a requirement. :)
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