Preview wrong on my machine: Y axis is stretched

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28 Nov 2014 18:11 #53513 by DaBit
I already posted this in the gmoccapy topic, but I did not get a useful response and it is not gmoccapy related.

So, I am having problems with the preview om my machine running the real configuration. The Y axis is stretched:



This is not gmoccapy-related; when I switch the display to AXIS it shows the same behaviour.

In a simulation configuration (sim.axis/sim.gmoccapy) the preview is OK:



When I fire up the configuration of my BF20, which is a parport driven stepper machine, the preview is OK too. Of course that configuration does nothing when run on the current Mesa-driven machine, but at least it is a realtime configuration.

The machine is running Lubuntu 12.04 with 3.4.55-rtai kernel (i set that up before the Debian-based distribution became available) and a RIP build of 2.8.0~pre

I am not sure when this issue started. I only started using the machine a couple of weeks ago so it has probably been present for a long time but I just did not notice it because I did not load G code programs before.

What did I do to figure out what goes wrong?
- Tried an ATI graphics card instead of onboard (Pentium G3258/H81 chipset): no change
- Started LinuxCNC with the LIBGL_ALWAYS_SOFTWARE=1 set: no change
- Used SSH+remote-X to start LinuxCNC on a local (mobaxterm) X server: no change
- Used a backup of the oldest configuration I could find that actually controlled the hardware properly: no change.
- Returned the servo period from 130000nsec to 1000000nsec: no change
- Disabled all unnecessary RT components, including all self written components: no change.
- Changed from a 4-axis machine to a 3-axis machine: no change in both AXIS and gmoccapy
- Downloaded and compiled LinuxCNC v2.6.4 as RIP in a separate directory: no change.
- Checked dmesg for errors or related messages: none found.
- Watched LinuxCNC output on the terminal: nothing.

I am at the point that only the servoloops are left in the HAL file using only LinuxCNC-supplied RT components. Tearing those loops down is a lot of work, so I though I could better ask here before doing so...

Any idea what might cause this?

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01 Dec 2014 01:42 #53545 by andypugh

I am at the point that only the servoloops are left in the HAL file using only LinuxCNC-supplied RT components. Tearing those loops down is a lot of work, so I though I could better ask here before doing so...
Any idea what might cause this?


I don't know what the cause is, but it is almost certainly nothing to do with HAL.

Do the parts come out correctly?

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01 Dec 2014 02:19 #53548 by DaBit
Yes, milling itself is flawless and the parts come out correctly.

It is only the preview that fails. And more specific: only the backplot, only in the Y direction, and independent of the GUI chosen (although I only tried axis and gmoccapy). The 'size bars' seem correct and at the right place. It also does not matter what kind of G-code generated the backplot; CAM-generated code with only G0/G1 lines is just as incorrect as handwritten code containing a couple of arc segments or G8x canned cycles. Circles become ovals.

I do not suspect HAL either, but it is still strange that a sim config or parport config works fine, but the 6i25 + 7i77 + PID loops config does not. There is a relationship. The problem is that I have no idea how to proceed in troubleshooting at this point without firing loose bullets and hoping to hit something.

Since I seem to be the only one running into this: could it be Ubuntu 12.04 + 3.4.55-rtai kernel related? It is not a supported configuration but I am a bit hesitant to install Wheezy since things like touchscreens, glade2, on screen keyboards, etc. seem to be more troublesome to get working.

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05 Dec 2014 22:13 #53718 by DaBit
OK, I got tired of it today and decided to install a fresh Debian Wheezy next to the existing Ubuntu 12.04.
That did not solve the problem; preview stayed stretched.

Upon close review of the INI file I found this:
..
..
PROGRAM_PREFIX = /home/dabit/linuxcnc/nc_files
INCREMENTS = 10mm 1mm .5mm .1mm .05mm .01mm .005mm
GEOMETRY =    XYYZ
CYCLE_TIME =          0.0500
..
..

The 'GEOMETRY=XYYZ' was remaining from the time when I setup the machine with gantrykins. Now I use it as a regular 3-axis machine and the second Y joint is dealt with outside the kinematics.

Change it to 'GEOMETRY=XYZ' and the preview is correct again.



I think that is a bug, BTW.

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