On Wed, 2 Feb 2022, gene heskett wrote:
Date: Wed, 02 Feb 2022 17:43:23 -0500
From: gene heskett <ghesk...@shentel.net>
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] Stepper PID
On Wednesday, February 2, 2022 5:21:34 PM EST Peter C. Wallace wrote:
On Wed, 2 Feb 2022, Thaddeus Waldner wrote:
Date: Wed, 2 Feb 2022 15:45:16 -0600
From: Thaddeus Waldner <thadw...@gmail.com>
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] Stepper
PID
I suspect that you are not using the DPLL, or that it is not setup
properly. For a RPI4 I would suggest these settings:
setp hm2_7i76e.0.dpll.01.timer-us -200
set hm2_7i76e.0.stepgen.timer-number 1
These should reduce the stepgenb position sampling jitter to a
fraction of 1 usec.
Thank you, Peter. I will check and see what the configuration looks
like later when I get home. Is there any documentation on how this
works? Also, what are the implications of increasing the dpll timer
period? If I can get away with 2ms
servo loop, should I set this to 400us?
No, the DPLL sample time setting is determined by jitter
statistics (average delay shifts = delay baseline drift),
not thread period.
If you change this value you should add it to the PID loops
FF2 parameter. This will compensate for the added delay between
the position read and velocity write. For -200 usec you would use
an added FF2 value of 0.0002 (PID values are scaled in seconds)
Peter Wallace
Mesa Electronics
Hhmm, and if there's no PID's in your config cuz you are using the new 3
phase stepper/servo's? These have encoders on the motors that don't get
fed to LCNC, only back to the driver, and among other things, the drivers
use the error they do detect to determine how much current is needed by
the motor to get there. Motors run 50C cooler.
Thank you Peter.
Cheers, Gene Heskett.
The Stepgen PID is used for most Ethernet configurations as it's more
tolerant of jitter than the built in stepgen position mode (and more tunable)
This is not related to the motor type, just to getting
the most accurate step/dir stream that is as immune to host
servo thread jitter as possible.
Peter Wallace
Mesa Electronics
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