Print starts promisingly, then drifts over max pos

Hi
I just finished my CoreXY printer that I run with 3Drag controller and Marlin. I have tried some dry runs on it and both the files tried start to "print" nicely but after a minute or so the printer stalls for a second and soon after that everything goes wrong. The endstops are not working and the printer tries to push through them making the belts slip on the pulleys (thankfully instead of braking everything). When I configure the controller board's Marlin, I see with the command M119 that the endstops work correctly. I have them set up as NC to avoid problems with loose connections and such, but it does not help a lot since for some reason the endstops just stop working when printing. Homeing works perfectly, and so do straight G-codes. Measurements are correct and I have margins on top of the max positions, but the machine calculates movements totally wrong and basically ignores the settings. I swapped the controller board and reflashed it with the Corexy configuration (I have 2 printers, the other is cartesian) to see if it is a hardware problem, but the same results.

I tried to upload the firmware with the newest Arduino IDE and that caused everything to be messed up - even the display was showing crazy stuff. Do you guys know a version of Arduino IDE that you have been able to upload a properly working CoreXY-Marlin on your board?

Any advise is appreciated.

Thanks!

Well I learned that the endstops are off on purpose when printing, so that's not an error even though I find that to be wrong, exactly because of stuff like my case. Othervise the problem remains unsolved.

I had similar problems at one point, turned out that one of the stepper pulleys was slipping.
(Caused by the stresses of calibration with bad end stop setup, and I hadn't put flats on the shaft)

Get a fine marker and put a line on the pulley and shaft then you can quickly see if this is the problem.

Have a look at the other endstop post in this section - it explains disabling 'endstops only for homing' - config.adv.h etc.

Printer stalls sounds like driver skipping perhaps -Its hard to diagnose which motor is at fault with corexy. Driver current? Acceleration? Slipping or skipping would cause a shift in position

Arduino IDE? Not Marlin you mean?

I've had no joy with the last two attempts to install new Marlin - Today and a month ago. Getting a blank screen and no comms to Pronterface. I'm sure I set it up same as previous.

Am using one from 7 Feb 15 ok but there has been some corexy additions (endstop homing issues fixed) since.

Not had a problem with the Arduino end, old or new.

-a