Reversing direction causes motors to jerk

I'm in the process of putting together a kit from Avid CNC (CNC Router Parts). I got everything setup and working, but one thing is vexing me. The machine runs super smooth as long as it's jogging in one direction, but every time a motor reverses, it jerks in the other direction instead of moving smoothly.

I uninstalled a motor to test on my workbench and got the same behavior. Super smooth rotating in one direction, but reversing direction causes the motor to jump. This happens both when I reverse direction immediately and when I wait a bit between direction changes.

All four motors do exactly the same thing.

I've tried a bunch of different acceleration settings from 1 up to 60 and they all behave the same way.

I've attached my current configuration file.

This is my hardware:

Linux CNC
Nema 34 stepper motors
Gecko GR214V drivers
Mesa 6I25/7I76 I/O cards

Here are a couple of videos where you can hear the CHUNK sound it makes when reversing direction:

vimeo.com/381842213
vimeo.com/381840195

This is how I have the drivers wired to the break out board:

P1 pin 2 (stp) -> 7I76s TB2 pin 3 (step0+)
P1 pin 3 (dir) -> 7I76s TB2 pin 5 (dir0+)
P1 pin 4 (+5v) -> 7I76s TB2 pin 6 (+5vp)

I tried several different timings, but they all behaved the same way. Here are two configurations I tried:

DIRSETUP = 100
DIRHOLD = 600
STEPLEN = 2000
STEPSPACE = 1000

DIRSETUP = 1000
DIRHOLD = 1000
STEPLEN = 4000
STEPSPACE = 3000

Anyone have an idea as to what the problem might be? Thanks in advance : )

Have you tried a lower acceleration?

It sounds mechanical. Like the acc eleration taking out the backlash

I’ve tried a bunch of accelerations from 1 to 60 and they all have the same jerk. Maybe I’m setting the acceleration wrong? I’ve been changing the max_accel in the config for each axis.

I don't experience a clunk with my plasma cutter with a rack and pinion drive.
I wonder if the clunk is a result of backlash in the spring loaded pinion.
When I started my build, I asked some questions about this on this thread
forum.linuxcnc.org/30-cnc-machines/31509...-loaded-pinion-drive
I don't know if it helps. But I went without a spring loaded pinion based on this thread..

Hmm, I suspect it's not a problem with the rack and pinion setup because 1. it happens to all 4 motors, even the Z-axis ball screw, 2. the motors jerk like this even when I run them disconnected from the machine, and 3. they do this no matter how loose or tight the tension is.

Is the motor current limiter set correct?

When you say "current limiter" are you referring to the Gecko drive or something else?

If you're referring to the drive, then I think I have it setup correctly, but this is my first time using them so I can't be sure.

Have you tried it with no backlash value?

Yep, I've tried both with and without a backlash value.

Time to share your hal and ini files as this is a user fault for sure.