Backlash issues on Y-AXIS

Backlash not working anymore in LinuxCNC v2.9.x

Build my own laser CNC machine about 4 years ago, which worked fine with LinuxCNC 2.8.2.
Using an RPi 3B+, laser and 2 x L293D controllers and 28BYJ-48 steppenmotors.

After trying to update Debian to trixie the SD-card would not boot anymore, so build new one (back to Bookworm).
(Although i can get the old data from LinuxCNC of the card.)
Debian Trixie is not that RT compatible as written all over, still need an RT version to run LinuxCNC on RPI 3B+.
Pitty there is no complete RPi 3 (only 4 and 5) version of LinuxCNC available anymore?

After installing LinuxCNC v2.9.6 (on Debian Bookworm) I could not get the machine working as it did with v2.8.2.
I also changed X-axis steppenmotor with a spindle drive to make it more accurate, this works fine (backlash between 0.1 - 0.3),
but after this I still have trouble with the Y-axis (on which i did not changed anything).
Before (v2.8.2) the Y-axis had a backlash of 1.315, but now I can not get it right anymore.
It looks like the backlash is now only working in 1 direction and I do not see the backlash correction back on the motor movement.
Even if I make the backlash much bigger, just to see if is really done by the motor.
It only draws (i.e. circles) bigger, but the error stays (see IMG_4618a.JPG with BL of 1, 2 and 3)

My question is what has been changed in v2.9.x according the backlash, as I only find 'improved'.
In my case it is not improved but getting worse.
Maybe the new changes do not work with my controllers (L293D)?
And how to solve this weird issue.

Reagrds, DG 

 

It's usually best to ask before you attemp to upgrade.

If it worked with 2.8.2, stick with 2.8.2.

Why do you want to upgrade?

Newer ≠ better.

Have you set backlash in you ini file ?

Unknown:
I am very sure the .ini file was added in the first post, but I don't see it anymore?
Here again.
And yes I mentioned BACKLASH in the JOINT_1 section of the Y-AXIS, otherwise there wouldn't be any difference between 1, 2 and 3 in the picture?   There the backlash was set to 1, 2 and 3.
Why does the picture get bigger (higher) instead of doing the backlash?

langdons:
After some years I thought it would be good idea to be 'up to date'.
What I always do with all my other Linux machines here, regularly
 

Has this always been the case, usually the write function is the last one in the list.

I Tried with 'hal_pi_gpio.write base-thread' at the end of the base-thread, but it does not make any difference.
Thanks for the info anyways.

In all honesty it may be worthwhile going back to you original setup. I generally think of the PC for a cnc setup as a "black box". As along as it doing everything you want leave it that way.
But it is quite curious as to why backlash is not working as expected. Maybe raising an issue on github may get better responses. The guys that do the coding will be answering.

I hate to say this but backlash comp should be a last resort after you have exhausted all mechanical ways to reduce it.

Sorry I haven't been able to solve this issue and I wish you all the best. If you do find a solution it would be great to describe the fix for anyone else in the future. Good luck as always.

tommylight wrote:

Your ini file is a mess and very hard to follow, but:
Y axis/joint has unreasonably big ferror and min_ferror values, probably should be close to what X axis has
Backlash_speed is set at 6000 inch !!!
-
What is the drive train? Belt? Screw? Ball screw?
Since it is a laser, i would advise belt only on X and Y.

 

I not even sure if there Backlash_speed is used in the hal file, there doesn't seem to be anything related to backlash_spped or similar mentioned in the docs for motmod.