On Friday 30 June 2017 10:12:31 Les Newell wrote:
> OK, this is embarrassing. It is noise and it has always been there.
> Anyone got any spare crows for me to eat? :-[
>
> > Do you have and raw-write encoder filter tweaking stuff in the hal
> > file: The bitfile may have changed so the address is no longer
> > correct (plus newwer version of the driver let you set these as hal
> > pins)
>
> You are correct. I had another trawl through the original hal files
> and found something that looks suspiciously like it tweaks the filter
> by directly writing to registers. I commented it out and the old setup
> behaves in a very similar way.
>
> As far as I can tell the problem is an earth loop between the drive
> and the computer. The drive power supply and computer are both earthed
> to the same star point but the ribbon cable also joins the drive and
> computer earths, forming a loop. I have now installed the computer I
> originally intended to use, which is a mini fanless pc powered by a
> double insulated power brick and the noise has gone. It runs perfectly
> with no filtering. The computer only has a mini PCI-e slot so I am
> using a mini PCI-e to PCI riser, with the 5I20 mounted in a separate
> frame beside the computer. If I had wanted to keep the original PC I
> probably could have fixed it by connecting the PC earth directly to
> the drive earth instead of to the star point. Earthing can be fun
> sometimes.
>
> It's ironic really. After I found the original installation wouldn't
> boot on the new computer I decided to work incrementally, doing a new
> install on the old computer then working from there. If I'd just said
> stuff it and installed the new version on the new computer it would
> have worked fine...
>
> Well, at least I have now proved you can use a 5i20 on a new computer
> using PCIE or mini PCIE.
> This is the PCI adapter
> <http://www.ebay.co.uk/itm/PCI-E-Express-X1-to-Dual-PCI-Riser-Extend-A
>dapter-Card-With-2-6-FT-USB3-0-Cable/131861478412>. They aren't
> available with a mPCIE plug so I had to buy a m-PCIE to PCIE adapter
> like this one:
> <http://www.ebay.co.uk/itm/PCI-E-USB-3-0-Express-1x-To16x-Mini-Extende
>r-Riser-Card-SATA-Adapter-Power-Cable/282475427399> just for the mPCIE
> plug and cable.
>
> Les
Les, when I have something like that, I often ask myself if it was worth
chewing thru the straps to get up and pee, last Monday morning. In
retrospect, the answer should have been no, several times now.
But I am glad you have it sorted. Is the 4 step pattern gone, or is it
the same even though it Just Works(TM) now?
>
> On 29/06/2017 22:29, Peter C. Wallace wrote:
> > On Thu, 29 Jun 2017, Les Newell wrote:
> >> Date: Thu, 29 Jun 2017 21:59:46 +0100
> >> From: Les Newell <les.new...@fastmail.co.uk>
> >> Reply-To: "Enhanced Machine Controller (EMC)"
> >> <emc-users@lists.sourceforge.net>
> >> To: emc-users@lists.sourceforge.net
> >> Subject: Re: [Emc-users] Rough motion with servos
> >>
> >>> Do you have and raw-write encoder filter tweaking stuff in the hal
> >>> file:
> >>
> >> No. For testing purposes I am running the barest minimum needed to
> >> achieve motion using a config generated by pncconf.
> >
> > If you did this before I would make sure you duplicate this
> >
> >
> > The default encoder filter is quite short even with the filter bit
> > on
> >
> > On a 5I20 its 15x30ns (filter bit on) so only 450 ns which is in the
> > range of coupled impulse noise spikes from the 7I29
> >
> > With current LinuxCNC dists (2.7 and 2.8) you can lower the encoder
> > sampling frequency by setting hm2_card.0.encoder.sample-frequency
> >
> > If you set this to say 5000000, This will result in a 15*200ns =3
> > usec filter on all encoder inputs that have their filter bit on,
> > This will limit the maximum count frequency to about 666 KHz and be
> > much more resistant to
> > coupled impulse noise from the motor PWM
> >
> >
> >
> > Peter Wallace
> > Mesa Electronics
> >
> > (\__/)
> > (='.'=) This is Bunny. Copy and paste bunny into your
> > (")_(") signature to help him gain world domination.
> >
> >
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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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