X and Y Axis skipping problem

Hi all

Pretty new to all this. I have a Prusa / Wade / Sanguinololuoloulo and I'm using Sk39 and Repsnapper.

I've been printing for a couple of weeks and I'm now starting to get reasonable print quality but I have an annoying problem with skipping X and Y axis.

Every now and again I hear a short scream/grunt from a stepper (like it's gone overspeed/overtorque) and the print misses one entire Gcode instruction (or that's the effect). So if I'm building a hollow cube and I get this, the build will continue but displaced by 1 width or 1 depth.

It isn't missing a step or number of steps on the motor, it's missing all the motorsteps for that G1 move. It appears the firmware is demanding the wrong speed for that move and the stepper is stalling for the entire move.

It's not the Gcode generation, I checked that. It's not the Axises themselves - they are smooth running and need a lot more resistance to stall the motor.

It's a random effect, sometimes it won't do it but usually it will at some point during the print, sometimes 2 or 3 times. I've tried different Duty Cycle settings between 0.25 and 1, no difference. I've tried different feed rates and higher print speeds seem to improve it a little but prints are then rubbish. Sometimes it's X, sometimes Y but not at the same time. Not sure if it's happening with Z or E axis as it's not apparent if it is.

I'm at a complete loss and pulling out what's left of my hair - any ideas?


Thanks

Graham

overheating of the drivers?
have you got a fan cooling your sanguino-polololus?

some other things to check out. Make sure you don';t have too much current going to the stepper. I know I had this problem when my steppers sounded like a charging camera flash.

you can also try ramping firmware like sprinter. It has a peripheral advantage of being easier on a stepper because it builds speed, taking advantage of momentum.

make sure everything moves smoothely back and forth on the rails, friction hurts.

check that the belt isn't climbing the fender washer or something similar, but it needs to be tight of course.

I ALSO recommend that you have heatsinks on the stepper drivers and a fan blowing on them.

Hmmm... very intriguing. My guess is, that since is is missing entire line of GCode, this must be a firmware issue... I don't think it has much to do with stepper drivers, as they only react to STEP and DIR signals, and that's all what they do. If you're missing entire line (which might be few hundred steps), it is definitely firmware-related.

I would
- reupload the firmware (Sprinter of course)
- if it doesn't help, try different firmware (TeaCup ?)
- take out and reinsert ATmega644P chipset, maybe it doesn't contact on one of the legs (?)
- check serial communication

Also, check the logs (in RepSnapper), maybe there is an error when sending GCodes. They're sent as ASCII text, so it happens (rarely) that one letter is lost.. usually it results in non-readable message, so firmware requests this line again. But if you're unlucky, this missing character might eat a dot in your F statement... say your GCode says:

G1 X139.4 Y50.95 Z0.19 F1440.0 E3.7836

after missing a dot in F statement it will be

G1 X139.4 Y50.95 Z0.19 F14400 E3.7836

with this feedrate, it will stall...

I am just guessing, I might be completely wrong though.. there should be checksum sent for every line of code, so these errors should not happen.

You might try to lower connection speed anyway, just in case.

i hope this helps

cheers

Przemek

test this out to see if gcode is actually missing, lower baud rate in firmware and in repsnapper to 19200baud

Had any luck Graham?

I've had endless trouble with skipping steps too - am currently looking at this [forums.reprap.org] but my hot end got into trouble before I could fully test it.

Sounds like your problem has slightly diffferent symptoms to mine but the effect is the same.

Let us know how you get on.

Thanks for your messages.

I've been otherwise preoccupied for the last few months but I'm back on the case...

I've had no progress but I could really do with some help on how to deal with firmware issues, as this is where things are pointing. I've not had to touch the firmware (Sprinter) to date, as it came preconfigured, and I don't even know how to start.

Any good 'idiot's guides' to firmware?



Thanks