On Wednesday 12 July 2017 15:05:45 R.L. Wurdack wrote:
> [OT] But the Megabot, giant robot guys (""Make"" magazine vol 58) are
> running rtai. Don't know what for.
>
>
> ----- Original Message -----
> From: "sam sokolik" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, July 12, 2017 11:13 AM
> Subject: Re: [Emc-users] Maybe we don't need rtai anymore?
>
> > here is a shot of linuxcnc running a 30us base period. You can see
> > the jitter on this analog scope.
> >
> > http://electronicsam.com/images/matsuura/20170712_130107.jpg
> >
> > Using parport resest (5us). So theoretically you could run close
> > to 30khz with rt_preempt on this system (3rd gen i5).
> >
> > sam
> >
> > (scope isn't calibrated very good)
> >
> > On 7/4/2017 10:15 PM, Jon Elson wrote:
> >> On 07/04/2017 05:22 PM, sam sokolik wrote:
> >>> Well - I have been playing with debian stretch and 4.9.0-3-rt
> >>> kernel. I booted our matsuura (j1900 quad core) which with no
> >>> tweeking has aprox 100us latency. (it has been running mesa
> >>> ethernet cards with rt_preempt - no issues) Next I booted it with
> >>> some kernel line tweaks. (checking the hardware - processors 0,1
> >>> and 2,3 share cache. So I added
> >>>
> >>> isolcpus=2,3 idle=poll
> >>>
> >>> The latency on this system was phenomenal. It has been running
> >>> for hours now and still <6us
> >>>
> >>>
> >>
> >> 6 us is quite good, although RTAI can do better on some boxes. But,
> >> 6 us is probably good for most interfaces.
> >>
> >> Jon
> >>
From what I have read, that looks like at least a 25% jitter, and that,
according to what I've read, will destroy around 75% of the torque
compared to a 1 or 2% jitter. That situation limits my toy mill, the hf
little one, to 8 to 10 ipm before the x/y motors will stall. Thats fast
enough to stall the spindle motor when a 1/4" upcut tool is in it,
turning 1500 revs, so my chips are thin and sharp. That slow of course
is also hard on the tools edge, particularly if plowing alu .025" deep
per pass. I have a 5i25 to put in it, and a 42 volt supply to replace
the 28 volts feeding the motor drivers now. But to explore that movement
increase, I'd have to also swap spindle motors, putting in the one I
took out of TLM years ago.
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Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
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