Stepper Motor Rotation Limit?

Not sure if this is the right board for this, but I'm in the process of upgrading the electronics on an old Dahlgren engraver I got for cheap. I have little experience with CNC hardware and I'm wondering if what I'm experiencing is normal, a hardware issue, or a software issue.

I'm running LinuxCNC 2.8 with a Mesa 7i96 board and a DM542 stepper driver. I'm using the z-axis motor for testing. It is an 8-wire motor which I believe is wired in parallel.

What I'm experiencing is that when I press and hold the keyboard key to move it, it will only spin for 8 full rotations and then it stops. If I lift the key and press it again, it continues to spin for another 8 rotations.

So is this normal, like a limit built into the jog function or something?

Thanks in advance!

Are you using Axis gui or are you using the test in stepconf linuxcnc.org/docs/html/config/stepconf.html

If you are then depending what setting you have at 7.1 Test area

[quote="dzawacki" post=155660
What I'm experiencing is that when I press and hold the keyboard key to move it, it will only spin for 8 full rotations and then it stops. If I lift the key and press it again, it continues to spin for another 8 rotations.

So is this normal, like a limit built into the jog function or something?
[/quote]
That is normal and it is spinning for the amount set between Min_limit and Max_limit in the ini file. for that axis.

Clive S wrote: Are you using Axis gui or are you using the test in stepconf linuxcnc.org/docs/html/config/stepconf.html

If you are then depending what setting you have at 7.1 Test area

Axis GUI

tommylight wrote:

dzawacki wrote: What I'm experiencing is that when I press and hold the keyboard key to move it, it will only spin for 8 full rotations and then it stops. If I lift the key and press it again, it continues to spin for another 8 rotations.

So is this normal, like a limit built into the jog function or something?

That is normal and it is spinning for the amount set between Min_limit and Max_limit in the ini file. for that axis.

Got it, I'll play with those settings so they're specific to my machine. Do those limits function similar to a limit switch with the caveat being that if you're in the middle of the bed, you'll still run off the edge?

It sounds to me like your were jogging in an increment mode rather than continuous mode, no?

Yeah, the software implements "soft limits" but they don't really do you any good if the machine doesn't know where it actually is. If you home first then the machine can use the soft limits effectively. Or if you even have a "parking spot" that you know the coordinates of and you can accurately tell the machine where it's at the soft limits would work then.

dzawacki wrote: ..............Do those limits function similar to a limit switch with the caveat being that if you're in the middle of the bed, you'll still run off the edge?

Yes.
There is a very simple solution to having the soft limit switches working at power up when the machine is not homed:
Add G0 X0 Y0 Z0 to the end of every gcode you run, that way the soft limit switches will be valid and prevent hitting hard stops.

this G0 X0 Y0 Z0 is only working if the HOME G53 is at that Location

You can use a User Mcode that calls a GO_Home or END_Programm Subroutine

like M120 User Mcode
o<endFile> call

filename endFile.ngc)
o<endFile> sub
G53
G0 z#<_ini[JOINT_2]HOME>
G0 x#<_ini[JOINT_0]HOME>
G0 y#<_ini[JOINT_1]HOME>
o<endFile> endsub
M2

DONT forget to set FEATHER VALUE to get read access
linuxcnc.org/docs/2.7/html/remap/remap.h...i_file_configuration