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Weird issue with stepper

Posted by silby1383 
Weird issue with stepper
September 20, 2011 03:39PM
I am just about done with my prusa build, however I have run into a snag. I am fairly sure I have a short somewhere in my wiring and was hoping somebody could give me some pointers.

I am running CAT5 from the steppers to a Male DB25 connector. My housing has RAMPS and power supply and cooling fans with a female DB25 connection. On the back side of the db25 I connect up all of the motors and endstops.

Because of this complex wiring (nightmare) I was hoping some tips could help me pinpoint where the problem would be without destroying too much (Pulling pins is a PITA!).

Problem, one stepper moves perfectly in one direction. In the negative direction (towards home) it stutters. If I do minus 10 steps it will only go -3 or -4 and stop. There is no buzzing or anything like that. I have full continuity between the connectors on RAMPS to the motor for all 4 wires.

Here is what I have tested:
1) Stepper motor is fine - I have plugged in the y axis from RAMPS into the stepper motor and it works fine.
2) stepper driver is fine - when I connect y or z to it it runs fine.
3) endstop seems to be fine. If I plug it into Y or Z it will stop those carriages without issue.

I am fairly confident it is somewhere in the X wiring. However what I cannot figure out is why this would only happen when running the motor in one direction. it makes me think that it is somehow related to an endstop.

Any thoughts would be greatly appreciated!
Re: Weird issue with stepper
September 20, 2011 04:03PM
Does the endstop on that axis function correctly, i.e. does it stop the axis moving one way?

It seems like the endstop signal is floating or picking up noise somehow and is intermittently stopping the axis. Could also be a bad ground on the endstop.

Re: Weird issue with stepper
September 20, 2011 04:19PM
If you plug the Y stepper into the X axis (on board) does the issue persist?
Re: Weird issue with stepper
September 20, 2011 04:38PM
Nophead - yes, the endstop does function correctly, ie, if I can engage it while it is traveling in the negative direction it will stop immediately.

Marnargulus, - When the Y stepper is plugged into the X it works fine.

It really seems as if it is the cabling for the x - however it doesn't make sense that the problem is only in the negative direction. I assume both stepper coils are used in both directions?

Thanks for your help!
Re: Weird issue with stepper
September 20, 2011 04:55PM
This sounds like a grounding issue, or an on and off short (where is shorts every once in a while). Does this happen at all speeds, or only higher speeds (Higher power = more potential for arcing)? Does the machine/wiring move around when you run the machine (if so try isolation everything above the machine so as few of the pieces move as possible).
Re: Weird issue with stepper
September 20, 2011 05:21PM
Yes the both coils are used in both directions. The only difference is the phase of the signals relative to each other. If it doesn't work in one direction it must either be a mechanical problem, or the endstop signal, as that is the only thing that affects one direction only.

Re: Weird issue with stepper
September 20, 2011 06:23PM
Thank you guys for your assistance. I will do some more troubleshooting tonight. I suspect that the end stop wire is probably shorted with the motor wire, that is probably why when I used a different motor wire it went away.
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