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Controller(pulse) frequency
« on: February 10, 2009, 02:45:52 PM »
How do I determine the proper controller/pulse frequency?  The manual seems pretty vague when it come to this setting in my opinion.  I also need help with the max step frequency for each axis.  How is this determined?

Thanks

Tom
1986 Hurco SM1 Stock ElectroCraft Servos and encoders, Larkin Viper 200 drives, Smoothstepper, CNC4PC C23 BOB, Dura Pulse GS3 VFD, Mach 3

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Re: Controller(pulse) frequency
« Reply #1 on: February 10, 2009, 03:24:48 PM »
Controller frequency will depend greatly on your computer, probably best at 2KHz but if you have problems withthe SS running out of buffer then go lower, if your computer has good communications you may find 4KHz will work fine for you, it does on all my machines but I tend to just run them at 2KHz anyway.
 As for the max step Frequ, set that to the setting just above what you require, eg if you have 20,000 steps per unit and rapid at 200IPM then that would be 20,000 x 200 = 4,000,000 per minute / 60 = 66.666 KHz so choose 128KHz as that is the next above. For any axis that is not being used choose the lowest.
Hood
Re: Controller(pulse) frequency
« Reply #2 on: May 13, 2009, 12:47:25 PM »
Hood,

I know this from some time ago but I just saw it.  Doesn't the acceleration and responsiveness of the the servo system increase with pulse frequency? I don't have a SS but when I increase the pulse frequency 2 or 3 times what is required for the max speed on my servos using the PP I don't see much rougher operation and am able to set a higher usable acceleration. If your required pulse frequency is less than 100K using the PP, what advantage would you get by upgrading to a SS, other than a more stable pulse stream?

Steve

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Re: Controller(pulse) frequency
« Reply #3 on: May 13, 2009, 04:18:22 PM »
I think Art has always recommended that you set the kernel to what you need and no more for the parallel port, why I am not 100% sure.
It seems strange that you get better accel if you set it faster than you need and I have not found that to be the case, maybe for some reason your computer is putting out cleaner pulses at a higher kernel.

I have found most of the parallel ports I have had in the past will mostly only be happy at 65KHz or less, 75KHz and 100KHz  have been unreliable, having said that I have been wanting to use the full kernel when in these modes due to the servos being capable of running at them.

As to whether there is a benefit to the SmoothStepper if you dont require a faster pulserate then that will depend, it certainly puts out a much cleaner pulse and often a difference in the motor can be heard even with the same pulserate as the PP had. Another benefit is it takes the pulsing away from Mach and leaves the computer to do the number crunching so freeing up resources, whether or not you will see a benefit I cant say. Some people can get better rapids and accel with the SS but if your PP is putting out a good enough pulse then you may not see any difference.

Hood
« Last Edit: May 13, 2009, 04:20:03 PM by Hood »
Re: Controller(pulse) frequency
« Reply #4 on: May 14, 2009, 11:31:58 AM »
Thanks, Hood.  I think Art's recommendation is based on keeping the load on your computer as low as possible and I fully understand that.  Do you see much degradation in your servo motor operation (smoothness) when you increase the SS pulse rate beyond the minimum required? I also am mindful of the fact that many servo drives, like Geckos are limited to 250KHZ until the G380s come out. So dialing up anything beyond that on SS would have unpredictable effects.

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Re: Controller(pulse) frequency
« Reply #5 on: May 14, 2009, 11:46:36 AM »
My servo drives have a max of 10MHz so they shouldnt have a problem with anything the SS can output :)
However during the Beta testing I am sure Greg said to keep the frequency for each axis to what you need and no more as it would waste resources in the SS so I have always done so.

Hood
Re: Controller(pulse) frequency
« Reply #6 on: August 08, 2009, 12:08:29 PM »
Hood
I noticed this back when it was first posted but thought it might still be right in application, now I'm not so sure. I crunched your numbers as above and see that your decimal point is to be 3 places further to the right ! or 66666.666 does this change things. I get a bit confused on these conversions ? I got to thinking of this when I had my SS stop and go offline for buffer error. I got to looking into the settings and trying it with a backed off setting. My pc is running in the 3gig range with very strong vid and ram. I was surprised that it had problem when run at 1ghrz and 64khrz. My servo settings are 20,000 x 110vel or by your math = 36666.666 or ? This is where I loose it ! What is the rest of the conversion or is this a simple displacement of decimal point ? as shows above ?
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  Don

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Re: Controller(pulse) frequency
« Reply #7 on: August 08, 2009, 06:24:42 PM »
My deciamal is 3 places to the left as I was saying in KHz, your 66666.666 is Hz.
For your settings 20,000 x 110 = 2,200,000 pulses per minute, divide by 60 to get per second (Hz) so  that  is 36666.666Hz, divide by 1000 to get KHz so that is 36.66666666666KHz
Hood
« Last Edit: August 08, 2009, 06:57:52 PM by Hood »
Re: Controller(pulse) frequency
« Reply #8 on: August 08, 2009, 07:12:45 PM »
Thanks, I thought that might be the case but wasn't sure
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  Don