Super slow velocity issues....

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

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

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...

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.

[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.

But review this

linuxcnc.org/docs/2.7/html/motion/tweaking-steppers.html

Also after reviewing the thread again and what Tommy said, review your homing setup. Here's mineSee
linuxcnc.org/docs/html/config/ini-homing.html

Running a 7i76e

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

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