Preview wrong on my machine: Y axis is stretched

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?

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.

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:

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.