Z-Stepper Skipping

Hi All,

Making progress here but am experiencing a new problem. One of my Z-steppers is slipping when it comes back up from hitting the endstop. You can see it because the z-axis couplers end up misaligned when that quick move is made. It doesn't happen on normal z-moves, up or down. Only on the backtrack after reaching the endstop. I tried switching one side out with my extruder stepper and the problem is a bit better but still slipping a bit. My electronics are RAMPS 1.4, Repetier firmware and host.

Any ideas?

Thanks,

KDog

I'm a new reprapper, so take this with a grain of salt but... The nut holders on the x-ends that the lead screws go through are sometimes not perfectly matched with the M8 nuts thus allowing a small amount of play when the lead screw changes directions. If that's the case, then you can correct it by wrapping the nuts in one or more layers of electrical tape before putting them in the holders. You want as tight of a fit as possible so there isn't any play.

Are your Z motors connected together in parallel?

Thanks for the comments.

I think that my z-coupler must be slipping. I'll check it tomorrow and see if I can't figure out how to fix it. The M8 nuts are really tight and the couplers are completely flush with each other (no gaps) so maybe they aren't holding during the reverse after reaching the endstop.

The RAMPS board has two connectors for the z-steppers on the board. Is it worth putting the stepper wires together and onto just one connector?

Cheers,

KDog

I haven't had any problems yet with my new build. Then again I haven't actually printed anything yet, just tested the motions, calibrated, set endstop positions, etc. I do have a pretty good understanding of electronics though. Assuming the stepper drivers use a constant current source the best way to wire the steppers would be in series since the current would be equalized for both steppers (as opposed to parallel where the voltage would be equalized and the current would depend on each stepper's coil resistance). It would probably put less stress on the stepper driver as well since it would need to pass half as much current. The two connectors on the RAMPS board are parallel wired, so you'd have to hook the steppers up yourself to get it series wired onto one connector. Then again it seems to work just fine as is.

Yep, sounds like one of your couplings is slipping

I had a similar problem, and it turned out to be just lack of lubrication of the Z axis screws, bit of oil and all ok.
My Z axis motors are wired in series, Marlin.

Thanks for the comments. I still haven't gotten a chance to try things out. I'm wondering though, how exactly do you wire your steppers in series. I talked to our electrical engineer about it and he said it wasn't straight forward.

KDog

Wiring the motors is not difficult to do, for a very good diagram have a look at
[www.reprap.org]
/wiki/RepRapPro_Mendel_wiring.
Then scroll down to. "The_Z_motor_wires"
This is for the Melzi controller which only has one terminal block for both motors, it is suggested they are wired in series.
You will need just two single connector blocks, to join the motors together, or better still, do it as suggested in the text and solder and sleeve the joints.
On Ramps you have two sockets, it doesn't matter which one you use.

Thanks again.

OK, here is what I've done:

1. Put new steppers on the z-axis.
2. Put new tubing on the z-steppers and re-tightened everything.
3. Rewired z-steppers in series.

Here is what is happening still.....

1. Both steppers appear to be turning the same speed when moving up or down and while homing.
2. When the end stop (hall sensor) is tripped the left stepper turns back about a 1/3 of a turn slowly and then resettles back to the end stop about a third of a turn. The right end stop turns over a full rotation back up and then back down very rapidly an entire turn.
3. The z-screws are not slipping as I put flags on the bottom of the screws and on the top of the steppers and they are both reacting the same.

This is really strange. The electronics are located on the left side towards the bottom of the printer. Not sure what to do now.

Any help is really appreciated.

KDog

Well I would agree with you - that's really strange.
If the two motors are the same and they are wired in series, then they really ought to behave in the same way.
I don't really have any answer. Looking at a schematic I found of the Ramps 1.4 controller, the outputs to the two Z steppers are wired pin to pin, so there would seem to be no way that a different command is being sent to the two motors.
My next move would be to try and eliminate any mechanical element, by disconnecting the coupling tubes and noting the results using your flags on the top of the steppers, obviously you'll have to operate the hall sensor by hand.
Other things that spring to mind is the drive voltage to the steppers, is it sufficient (hard for you to know) Is the current limit (if there is one on Ramps) set too low, Steppers can do odd things with incorrect drive, and one may have slightly different thresholds to the other, but your symptoms don't really come into the normal odd category.
Good Luck.

Hi,
I'm experiencing almost the same problem. In fact I have an Orca v042 and during the 3 first layers, the Z stepper dosen't work! it skips them, then gets back to work normally starting from the 4th layer.
any suggestions?
kindest regards

Not sure why you would want to connect them in series when the ramps board is designed to wire them both together(in Parallel)

That's a very good point, Series connection would actually need a higher voltage drive, It's easy to loose sight of what did and didn't work previously. if changing from parallel to series made no difference, then put it back. You may well have done something else since that would make a difference.

Easy enough to put the steppers back to parallel. The idea to decouple the steppers is a good one. I'm going to check that out next session...am a little afraid of what to do if that doesn't work! Can there be any interference from any of the other wires, motors, etc., that could case this behavior? I have an extra stepper driver that I can try as well.

Thanks again for all the ideas.

KDog

Any chance of a video of the problem occurring?

Thanks for the support while I worked through this frustrating issue. I swapped everything back to how I had it when I first discovered this problem. Problem was still occurring. Tried swapping out driver boards, didn't do anything. Finally swapped out RAMPS with a spare that I have for a new printer I'm working on....problem is gone. Still not sure how this could be caused, even by a bad board. But tired of working on it now so guess I'll just keep on going with the new board for now. Any more ideas?

KDog

ops nvm ...

Edited 1 time(s). Last edit at 03/07/2013 05:12AM by redreprap.

sheck626 Wrote:
-------------------------------------------------------
> I'm a new reprapper, so take this with a grain of
> salt but... The nut holders on the x-ends that
> the lead screws go through are sometimes not
> perfectly matched with the M8 nuts thus allowing a
> small amount of play when the lead screw changes
> directions. If that's the case, then you can
> correct it by wrapping the nuts in one or more
> layers of electrical tape before putting them in
> the holders. You want as tight of a fit as
> possible so there isn't any play.

I found my nuts had quite a bit of play, which I think could cause a big problem as the z rods only turn a little each time. If the head is raised and dropped for each layer this could cause significant backlash.

After reading your comment I tightened the fit using masking tape. Unfortunately I tightened both nuts, which caused the rods to lock. I now just have the bottom nuts tightened, and hope it will make an improvement