On 06/29/2017 10:20 AM, Les Newell wrote:
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.
Assuming the spikes happen fairly often, you should try
setting up Halscope to display velocity and trigger on where
you think a spike might reach, and then move the axis by
hand for a while and see if the scope triggers. This would
be with the drives off and moving it by hand. If you can't
see these spikes with the drives off, then you have a strong
indication of electrical noise getting into the encoder
signals. Mesa does have some adjustments to the digital
filter settings that you could try, or you may need to
change the encoder cables, set up the shields differently
(you ARE using shielded cables, I hope!) of possibly have to
go to differential drive at the encoder end, with
differential receivers at the Mesa end.
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?
I think you are on the right track.
Jon
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