Noob pulling hair out: X-Axis travels 2X distance, prints 2X length

I bought a Prusia I3 kit from China and have everything working short of the final tweaks with the exception of the X-Axis travel and I can’t seem to find a solution to save my life. Strikes me that this should be an easy fix and the answer may well be staring me in the face, but I’m tapped and any suggestions at this point would be EXTREMELY helpful.

Basically, it is traveling twice what it should and printing twice what it should. When I tell it to move 50mm in Repetier, it moves 100mm. When it has moved 200mm to the edge of the plate, both Repetier and the LCD on the machine show 100mm on the display. Prints are exactly twice as long as they should be along the X-Axis and prints start at the far right of the 200mm wide plate instead of center. Here is what I have checked so far:

1) Configured and reinstalled firmware three times, from three different sources. Checked firmware thoroughly, line by line, using multiple web sources for guidance. Has the same travel scales and limits set for the Y-Axis that works perfectly. The one positive thing out of this mess is I’ve really gotten to know that script! Repetier configurations appear correct and re-checked multiple times.

2) Endstops are good—it homes perfectly.

3) Moved the extruder to the far (what it thinks is 100mm) right X-Axis and took the motor and belt off. Continued to move to the full 200mm in Repetier and then reinstalled the motor and belt and homed. Tried moving again with Repetier and still the same problem—it moves 100mm when I tell it to move 50mm, etc.

4) Entertained the idea that maybe it was accidentally set for two extruders, but this is definitely not the case.

5) Switched wiring for X and Y Axis just for peace of mind, at which point Y began behaving as X was, so it is not a mechanical problem with the X-Axis motor.

Probably tried a couple other things I’m not thinking of right now, but I’m about out of gas and nothing on the web is jumping out at me. Like I said, it seems like this one should be easy……..

no mention of electronics... which is where the issue lies

Most board have a bunch of jumpers to set micostepping on the stepper driver. On ramps its under the Polulo modules

Sounds like you have a missing jumper (or bad solder joint on the jumper pins, or on pololu module, or even missing metal from inside the jumper)

Most are configured for 1/16 micosteping, but if one jumper is missing or not working the axis is set for 1/8 micostepping and moves twice what its ment to.

Edited 2 time(s). Last edit at 08/24/2015 11:24PM by Dust.

Probably Dust is correct, but it could also be a misconfiguration in the software... it sounds like your X axis is set to exactly twice the steps/mm that it should be. See the Prusa Calculator

It’s a MKS GEN-2Z V1.1 board. And thanks for the input!

OK, so let’s be sure we are speaking the same language here. On this board what I would call a stepper driver or controller is pinned to a set of risers next to where the cable to the motor would plug in? If we are on the same page, then to troubleshoot what do you suggest? All I can think of is to pull the driver and inspect it for soldier bridges or missed soldier joints. Maybe swap it with the Y-Axis to see what happens and see if I can isolate it that way? These were already installed on the board when I received the kit.

Some pretty tiny soldier points on these things. Safe to assume it isn’t worth attempting repair if I actually see something or isolate it to that stepper driver? I work on vintage electronics as a hobby but generally don’t mess with stuff that small if I can avoid it--too easy to bridge joints.

If you have not identified the problem and you are desperate to print some beautiful things, then a quick fix would be change the steps per mm for your x-axis in firmware by a factor of two.
But I also think the problem is most likely the microstepping. If you remove the stepper drivers for the x axis and y axis on your MKS GEN-2Z, they should both have
three jumpers below. If they do, remove them and put them back, and if the problem remains look for bad soldering or missing pins. If not, then replace the missing jumper and you
should be on.

Not knowing that board it looks like there are jumpers for the steps under the drivers.
Below are settings I found.



Microstepping

MKS Gen contain a row of 3 jumpers.

with DRV8825

1 2 3 step mode
0 0 0 Full step (2-phase excitation) with 71% current
1 0 0 1/2 step (1-2 phase excitation)
0 1 0 1/4 step (W1-2 phase excitation)
1 1 0 8 microsteps / step
0 0 1 16 microsteps / step
1 0 1 32 microsteps / step
0 1 1 32 microsteps / step
1 1 1 32 microsteps / step

with A4988

1 2 3 step mode
0 0 0 Full step
1 0 0 1/2 step
0 1 0 1/4 step
1 1 0 8 microsteps / step
1 1 1 16 microsteps / step

Yeah, I follow you. I looked at a picture of the board with nothing on the risers and see the jumper pins you guys are talking about--not going to be able to get into it until tomorrow or maybe later this evening if I have a second. Thanks for the tips!

Well, I suspect we are on the right track, but no closer to fixing this thing. Looked like one jumper was loose and faced a different direction than the other two (not that it should matter), so I adjusted the tension on the pins a little and put it back in and did the same with the other two. Still the same problem. Switched out the stepper driver with the Y-Axis stepper driver and still no change, with the Y-Axis working fine with the former X-Axis driver, so that factor is now ruled out.

I then began to take out jumper pins from the X-Axis to see how it reacted and and got more of the same on each configuration. It was doing the same thing with one jumper, two jumpers, no jumpers and, of course, the three that it is supposed to have. Shouldn't the jumpers affect the travel?

Soldier joints look good on the mobo, as well. Any other ideas? I suppose maybe swapping the board is starting to loom as an option, but I'm stubborn about this sort of thing.....

What are the actual values of the steps per mm section in configuration.h? Does it work when you half the numbers?

You could try measuring the MS1 MS2 and MS3 pins on the stepperstick if they read about 5V. If not, then there's your problem. These pins are pulled down by default, so if nothing is connected to these pins the pins read as low (GND).
stepstick

Next step is to find out if the jumpers have a good connection to the ms1..3 pins. It could be a via that's not connecting properly. You could try to find the tracks on the board and solder a wire in the vias but it would be easier to swap the board.

Thanks! That worked, but I don’t understand why. It crossed my mind to try that on Saturday and I talked myself out of it because I didn’t see what difference it would make—and still don’t. Clearly I don’t understand this aspect of the settings properly. This is what I had:

#define DEFAULT_AXIS_STEPS_PER_UNIT {80.5,80.5,405.6,80.5}

Changed it to:

#define DEFAULT_AXIS_STEPS_PER_UNIT {40.2,80.5,405.6,80.5}

Since X and Y travel approximately the same distances shouldn’t the steps per mm be the same? When I halved the X steps per mm, it travels the whole 200mm and the prints I kicked out were in spec.

So can I limp along as it is or does this identify a hardware issue? No time to bench test any hardware until the weekend, but I want to keep this thread open until I get this hammered out.

Check the x stepper motor degrees per step on the sticker. It may be 3.6 degrees per step instead of the assumed 1.8 degrees. If it's 1.8, then check the pulley number of teeth and belt pitch. Finally measure the stepsticks ms1..3 pins to check the microstepping. Microstepping is a trick to get the motor to turn in smaller steps than it is rated for in factors of 2, 4, 8, 16 and 32 depending on stepsticks. If all else checks out, it could e that microstepping is stuck at 8 instead of 16.

See Triffid hunter calibration guide for the formula to calculate the steps per mm. Your 80.5 seems odd though. Usually it's 80.
triffid hunter calibration guide

You’re right—it should be 80. As for the motor, it is supposed to be 1.8 deg—what are the chances that I was given a 3.6 by mistake? None of them have any markings. If that is, indeed, the case then I imagine it’s a good thing I didn’t install it on the Z.

I’ll do the other tests tomorrow.

=You can attach the y stepper motor to the x port and see what it does, or connect the x motor to the y connector. If the x motor displays the same behavior then it's highly likely it's a 3.8 degrees per step motor. If the y motor displays the same behavior on the x connector it's probably the microstepping.
Be sure to turn off all power to the board when swapping motors.

Edited 2 time(s). Last edit at 08/28/2015 02:02AM by imqqmi.

I got it--thanks! Bad jumper--should have noticed in the first place but I built the thing on my coffee table with not the greatest lighting. No metal clip on the inside--just plastic!

Glad you've found the problem!