On Wed, 2 Feb 2022, gene heskett wrote:
Date: Wed, 02 Feb 2022 14:43:07 -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 1:57:33 PM EST Peter C. Wallace wrote:
On Wed, 2 Feb 2022, Thaddeus Waldner wrote:
> Date: Wed, 2 Feb 2022 01:39:29 -0600
> From: Thaddeus Waldner <thadw...@gmail.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
>
> <emc-users@lists.sourceforge.net>
>
> To: Enhanced Machine Controller <emc-users@lists.sourceforge.net>
> Subject: [Emc-users] Stepper PID
>
> ????Hi,
>
>I have a pi4 running the 2.8.2 iso. I have it connected to a Mesa 7i96
>and from there I????m driving small stepper motors with tmc2209
>????stepstick???? drivers. I think my step rate at max speed is around
>8khz
>
>I get around +-70us? Max latency.
>
>I????ve been having an issue with what I think is latency which makes
>the steppers sound like they have bad bearings. Raising the servo
>period to 2ms made it worse. So I tried a faster servo thread and
>discovered the issue pretty much goes away with the servo period at
>250us. At that rate I start running into joint following issues. 5A I
>then learned that with the servo period at 1ms, if I lower the
>stepper PID P parameter to 100 instead of the 1000 set by the
>configuration wizard, the noise goes away completely and the steppers
>run buttery smooth.
>
>I have a few questions:
>1) what are the implications of running the PID stepper with p=100?
Worse following error
2>) why is servo thread jitter even making into the stepper pulse train
with a
>Mesa Ethernet card and no communication errors? Do I have anything
>misconfigured?
The problem is that the PID loop makes bogus velocity corrections
because of position sample time jitter (which may be as high as a few
hunderd usec on RPI4 Ethernet)
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
With no previous guidance, I set my 7i90 with SPI interface at -50 u-
secs, should I raise that?
Its probably OK as SPI has less added jitter than Ethernet.
200 usec is probably overkill but it needs to accomodate
the worst case base-line wander.
set hm2_7i76e.0.stepgen.timer-number 1
These should reduce the stepgenb position sampling jitter to a
fraction of 1 usec.
>Thanks
Peter Wallace
Mesa Electronics
Thanks, stay well Peter.
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, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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Mesa Electronics
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