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-Adapter-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-Extender-Riser-Card-SATA-Adapter-Power-Cable/282475427399>
just for the mPCIE plug and cable.
Les
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
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