On Thu, 29 Jun 2017, Les Newell wrote:
Date: Thu, 29 Jun 2017 16:20:16 +0100
From: Les Newell <les.new...@fastmail.co.uk>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Rough motion with servos
Well, some progress figuring out what is going on.
I just ran some more tests using Ubuntu 16.04 with a freshly built preempt-rt
kernel and freshly built Git master. No surprise, it still shows the fault. I
took a Halscope log from the original setup. The encoder velocity is rather
noisy but no big spikes. On the new install the encoder velocity is not as
noisy but it has occasional spikes. The encoders are wired to a 7i29.
This log is from the old setup <www.sheetcam.com/lathe/old.log>
This log is from the new setup <www.sheetcam.com/lathe/spike.log>
This lathe is fitted with high resolution handwheel encoders so I also did
something I should have done much sooner and looked at the handwheel encoder
velocity. Big difference - nice clean signals on both configs.
So it looks like something funky is going on when reading encoders with the
7i29, resulting in noisy velocity estimation. I guess the velocity estimation
code has changed a bit over the years, giving the different results. The
fault has probably been there for a long time, quite possibly since I built
it. My immediate thought is noise on the encoder signals but this machine
never loses position. It will turn out accurate parts all day. Peter, any
idea how the velocity estimation can be noisy while the overall counts seem
to track accurately?
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)
Note the noise in the encoder signals can generate nasty velocity noise
without losing counts
Some time back I was involved with developing flight controllers for RC
models. They used nested PID loops. The loops worked well even though the
accelerometer and gyro feedback signals were extremely noisy. I think that
explains why my old config seems to run smoothly. The signal is noisy but
consistent so the noise averages out. On the later config the velocity
estimation ends up with spikes which are noticeable in motion.
Les
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Peter Wallace
Mesa Electronics
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