Super slow velocity issues....

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26 Mar 2017 22:17 #90318 by nigel-tufnel
I am having issues with my Y-axis homing using AXIS but not my X-axis homing. The issue is that once it hits the Y-axis limit switch and starts to very slowly step out of the limit, AXIS thinks its moving but there is no actual movement. I've traced it back to the Y-axis cannot make very slow movements (below ~2in/min). The X-axis can make slower movements. Is there a variable that controls the minimum velocity or does this sound like stepper driver issues? Any suggestions on where to look would be appreciated. Thanks

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26 Mar 2017 23:59 #90324 by tommylight
In the ini file under the joint 1 for Y axis there are several enties for homing, below the home_search_velocity is the one you should change named home_latch_velocity.
By default it is set very low.
Is there any particular reason why Y axis will not move at lower speeds ? That is not how it should be, on all the machines i can move any axis at an extreemly low speed.

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27 Mar 2017 00:38 #90326 by nigel-tufnel
Thanks for the response. I'm aware of the home_latch_velocity and I increased that as a stop-gap measure.

There is no reason that I am aware of why the Y axis should not move at lower speeds. I was hoping someone has some ideas.

I forgot to mention the following hardware in my original post:
-1.8deg stepper (x10 microstepping)
-Mesa 5i25/7i76
-Gecko 202 stepper driver

Thanks

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27 Mar 2017 08:21 #90336 by rodw
Replied by rodw on topic Super slow velocity issues....
I saw a post recently from PCW where he said the Gecko 540 struggles at low velocities and your stepper is a very close relative..... try increasing the step length >5,000 was something he said...

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16 May 2017 00:20 #93244 by nigel-tufnel
I contacted Gecko about this issue and they said it didn't sound right and to send back the drive for evaluation. I sent the drive back but they indicated "no problem found". It still exhibits this behavior.

Anyone else have any ideas on what might be causing this? (again I'm using Mesa 5i25/7i76)

RodW - can you elaborate on how/where to change the step length? I didn't see anything that look like it in my .ini file. I fear editing with the Config wizard again because I have custom tweaks to my hal and ini files I don't want to risk.

I wanted to do one last attempt at fixing before buying a new stepper drive that may or may not fix the issue.

Thanks.

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16 May 2017 02:30 - 16 May 2017 02:36 #93248 by rodw
Replied by rodw on topic Super slow velocity issues....
[quote="nigel-tufnel" post=93244}

RodW - can you elaborate on how/where to change the step length? I didn't see anything that look like it in my .ini file. I fear editing with the Config wizard again because I have custom tweaks to my hal and ini files I don't want to risk.

Thanks.[/quote]


In your ini file under each joint but mine will be waaay tooo short.
DIRSETUP   = 500
DIRHOLD    = 500
STEPLEN    = 1500
STEPSPACE  = 1500

But review this

linuxcnc.org/docs/2.7/html/motion/tweaking-steppers.html
Last edit: 16 May 2017 02:36 by rodw.

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16 May 2017 02:39 #93249 by rodw
Replied by rodw on topic Super slow velocity issues....
Also after reviewing the thread again and what Tommy said, review your homing setup. Here's mine
HOME_OFFSET = 45
HOME_SEARCH_VEL = 0 
HOME_FINAL_VEL = 100
HOME_USE_INDEX = NO
HOME_SEQUENCE = -1
See
linuxcnc.org/docs/html/config/ini-homing.html

Running a 7i76e

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11 Jun 2017 19:12 #94411 by nigel-tufnel
Thanks Rod. I increased the STEPLEN value and I was able to make slow movements. However, this one axis is not as smooth as the other axes at slow speeds so it seems like there is more options for tuning. Below are my settings before increasing the STEPLEN.

DIRSETUP = 1000
DIRHOLD = 5000
STEPLEN = 500
STEPSPACE = 4500

If I increase the STEPLEN, do any of the other corresponding variables need to change accordingly? I'm using a Gecko G202. www.geckodrive.com/g202.html

Any suggested values appreciated. Thanks

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11 Jun 2017 21:39 - 11 Jun 2017 21:39 #94418 by PCW
Replied by PCW on topic Super slow velocity issues....
Unless the settings are limiting your maximum speed there's usually no reason not to use longer step timings
in addition, long direction setup and hold times have very minimal effect on performance so

DIRSETUP = 20000
DIRHOLD = 20000
STEPLEN = 5000
STEPSPACE = 5000

is a good starting point that will work with almost all drives.


Note the this will limit you to 100 KHz maximum step rate
Last edit: 11 Jun 2017 21:39 by PCW.
The following user(s) said Thank You: rodw

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