Setting up a gantry with 4 joints and 3 axes

I have a gantry that I am trying to set up as a 4-joint, 3-axis machine so I'll be able to easily home and square the two motors on the Y axis. I've been scouring the documentation to try to figure this out and have run into a wall. I'm asking this on the stepconf section because I used that wizard to make my current profile, and hope I can use it for this change as I don't have experience editing config files directly.

I gather that I need to:
* upgrade my version, (but I can't tell to what version)
* start the new version of LinuxCNC, at which point a script should update my configuration to joints/axes format
* do some editing of the configuration to define and link the two Y-axis joints

So far I have updated to version 2.7.12 and 2.7.12-23-gade72db (with the AXIS interface). After booting both versions I checked my config directory and the .ini file was unchanged, which made me think the script hadn't updated for joints/axes mode.

QUESTIONS: Am I using the right version? If so, how do I get at the joints/axes functionality? Am I posting in the right forum section?

Thanks very much!

--Abe

The correct version for the updated gantry configuration is "Master" aka 2.8pre. It is unreleased and "caveat emptor" -- but several contributors are using it every day just fine.

I'd suggest you update as described here: forum.linuxcnc.org/9-installing-linuxcnc...l-current-master-2-8

Then read through a recent similar journey here: forum.linuxcnc.org/39-pncconf/34051-2-st...n-one-axis-5i25-7i76

That thread has specifics for a Mesa card and the associated config app, PNCConf instead of Stepconf -- but the outline of required file changes is the same. You create a 4-axis XYZA configuration in Stepconf, then make manual edits to convert the A axis to the 2nd "joint" of the combined Y-axis. All the details and caveats are in that discussion.

Thank you! I just installed 2.8pre and we'll see where that takes me...

Just be aware that as of 48 hours ago, master branch had a regression in the homing using the axis GUI. If its not working for you then change to the Gmocappy interface (which is editing one line in the ini file.)

I will post up a minimalist config I created for Chris Morley using Mesa hardware. Chris knows about it so I am hoping its been fixed by now. (but I compiled from source, so the deb install might lag behind this.)

Interesting you mentioned "one line" change to get Gmoccapy -- I tried that one change today (from a known-good Axis ini/hal combo) and it barked about around 20 missing items. I didn't track them all down, but I'll be trying again later this week.

I finally got a chance to try these suggestions, and now I have more questions!

DanMN:
Looking at the thread with chadrat6458, all I see in the INI file is that you moved the block for JOINT_3 up with JOINT_1, you changed two references of XYZA to XYZY, and you made sure the new Y joint was LINEAR, not ANGULAR. To configure my 2-Y-motor gantry, I also modified the .INI file with those three changes. Was there more I should have done? My INI file is attached.

I made no changes to my HAL file, which is also attached.

When I start LinuxCNC I can run the X and Z axes just fine, but only one motor runs on the Y axis. Also, the homing menu doesn't give me an option to home the Y axis.

Does anyone have a suggestion? As you can tell, I don't have a grasp of how the joints and axes are linked to each other in the INI file, and I wonder if that is the problem.

Thanks,
Abe

Just noticed the values in my INI file were different for the two Y joints. They're fixed in the attached file, which still doesn't work.

The first obvious error I see is that the HOME_SEQUENCE = lines for joints 1 and 3 (the Y joints ) should have the same negative number so Linuxcnc knows to home them together as a slaved pair.

So set them to HOME_SEQUENCE = -2

Thanks, Todd. I set HOME_SEQUENCE = -2 on joints 1 and 3 in the INI file, and now when I try to jog the Y axis it says "Homing is REQUIRED to jog requested coordinate because joint (1) in home_sequence is negative (-2)". There is still no option to home the Y axis in the Machine>Homing menu.

Thanks,
Abe

A couple of best practices I'll point out first:

1. I moved the Y-axes together in the INI file so that it's easier to scan for differences between the Y joint configurations. Trust me, you do not want differences there.
2. ALWAYS edit one Y joint and paste it whole-hog into the other Y joint config. If you make a typo and add-in/leave-out a minus sign on a HOME_SEARCH_VEL or SCALE entry (for instance) you would send the two ends of your gantry in conflicting directions. Same thing if you were playing with offsets or home position. One joint stops while the other keeps going. Giving different instructions to the two axes is bad. Groan-screech-pop-zing-cursing bad. Very bad.

As Todd points out, you must make the controller aware that Joints 1 & 3 are designated to a single axis -- and the absolutely unintuitive way that is accomplished is by assigning them both the same negative homing sequence number.