Random motion and lost steps after upgrade

andypugh wrote:

I think it is unlikely that the changes to LinuxCNC are the cause of this:

linuxcnc.org/2016/07/31/LinuxCNC-2.7.6/
linuxcnc.org/2016/09/08/LinuxCNC-2.7.7/

Can you check that you are still using the right kernel? (uname -r command)

Good idea, but it is still RTAI:
3.4-9-rtai-686-pae

I'll make the next days some tests
a) with the up to date set up I just use a toothpick as "cutting tool" to prevent further costs (have a tool length sensor; So I need something as a dummy)...Let's see if the error is in any kind reproducible
b) if it still comes up I switch back to 2.7.5 and retest. Let's see if the error happens there, too.

What are you ferror settings?

On all achsis I have FERROR = 1 and min = 0.25
(the standard according to the doc seems to be min = 0.01 but I'm not sure anymore if/why I had changes this. Was years ago...)

Is this ferror only applicable for servos? I have regular stepper motors.
I'll post my hal/ini tomorrow. It is now midnight in Germany.

If those are mm and the problem is real that suggests the error is in the trajectory planner

The step generator is effectively a velocity mode servo system

Yes, all settings are for mm in my ini/hal. Attached is now a backup of the config as tar.gz
The problem seems only to be the Z achsis; X/Y work fine.
Z achsis is adjusted to be 0 at the ground and then with positive values the higher you go. Means you typically mill between 0 and 20 mm.

I'll make some tests with 2.7.7 now to see if I can enforce a wrongdoing.

sorry, but I've been really busy the last few days to reply back! anyway, I've done everything that i could think of, used two different computers, onboard and off board parallel ports, and even a complete re-install and scratch hal and ini's all to no avail. in the end, i just ended up downgrading down to 2.6 and all works well, just no JA homing

I haven't really had the chance to put it through it's paces, but so far all seems to be on track. I even did a complete re-install from the 2.7 wheezy image and upgraded to 2.8pre and the problem still would not go away. soon as i rolled back to 2.6 on lucid, everything seems to work great. maybe my computer hates wheezy, i know i do!

The acceleration and velocity profiles can be quite different with the new vs old trajectory planner. Have you tried running 2.7 or 2.8 with the new planner disabled?
In your ini file under the [TRAJ] section find ARC_BLEND_ENABLE = 1 and change it to 0 That should revert the trajectory planning back to the old system. See if that might make a difference for you. It is possible that your config settings for the Z are borderline enough that the higher performance of the new planner pushes them over the edge.