Y-Axis can't find zero right

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Toby
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Re: Y-Axis can't find zero right

Post by Toby » Mon Apr 21, 2014 12:42 am

jsc wrote:What I am interested in is if it ever stops short when you are not using the Home Y button, just when it is commanded to do a long y axis travel move.
Michael correct me if I'm wrong, but I think the answer is it never stops short on a direct G1 Yxxx command, only on a G28 home command. In terms of the GCode Jin suggested, what is being described is this behavior:

1. On the home command the bed stops short and marlin thinks it is at y=0, though the end stop is not tripped.
2. When he then puts in G1 Y250, it goes to 250 but overshoots, and has to be stopped by emergency cutoff to save the steppers. Makes sense given 1.
3. On the G1 Y0 command the bed moves all the way to endstop. (That could be odd but given the disconnect in step 2 maybe not.)

So it seems to depend on the home command getting to marlin, where something funny happens during the execution. My plan is to have a look at the code for homing and see if I can get a sense of what might be going on, but anyone interested and more familiar with the marlin source, go for it.

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MichaelH
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Re: Y-Axis can't find zero right

Post by MichaelH » Mon Apr 21, 2014 1:15 am

Hi Toby,
sorry I didn't attach the GCode in first place, I fixed that.
jsc wrote:
What I am interested in is if it ever stops short when you are not using the Home Y button, just when it is commanded to do a long y axis travel move.
Y-Axis move test.rar
Y-Axis move test
(161 Bytes) Downloaded 211 times
Michael correct me if I'm wrong, but I think the answer is it never stops short on a direct G1 Yxxx command, only on a G28 home command. In terms of the GCode Jin suggested, what is being described is this behavior:
Yes I have to correct you because it does stop with a G1 Yxxx command as well.
The GCode attached is the one I used for jsc's suggestion.

Michael

Toby
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Re: Y-Axis can't find zero right

Post by Toby » Mon Apr 21, 2014 6:36 am

MichaelH wrote: Yes I have to correct you because it does stop with a G1 Yxxx command as well.
The GCode attached is the one I used for jsc's suggestion.
Did I also misunderstand the earlier result that if you put the bed at y=250 and jog by increments to y=0 then it does not stop along the way? If that was right, then does there seem to be some minimum travel distance needed to get it to stop early?

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MichaelH
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Re: Y-Axis can't find zero right

Post by MichaelH » Mon Apr 21, 2014 10:47 pm

Hi Toby,

No you didn't misunderstood at that time.
But I tied again after the the last attempt with 30 mm steps and it happened again I can't get any lower in order to get a clear result.
I don't know if it just didn't happened last time. :cry:

Michael

Toby
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Re: Y-Axis can't find zero right

Post by Toby » Tue Apr 22, 2014 8:21 am

Hi Michael,

Okay that's good to know. I've got the Marlin source and have started poking around in it to see what makes sense to try next. So far it doesn't look too complex, but I haven't tried making any changes and recompiling etc so I'm not sure what that entails. Theoretically your problem has got to be traceable. There's nowhere for it to hide at this level.

Toby

Toby
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Re: Y-Axis can't find zero right

Post by Toby » Tue Apr 22, 2014 5:24 pm

Michael, No surprise that your firmware shows Y=0 when the bed stops early. From a first scan through the firmware, it appears to set y=0 the moment you Home, so it's going to show that no matter what actually happens.

Next thing is to look at how the motion control works- again just from a first scan through the firmware it appears it sets it up in a buffer and then reads the buffer to perform the moves. So maybe there are multiple items in the buffer on a long move and for some reason sometimes one or more get discarded? Just guessing to have something to look for while I'm learning my way around....

Have you tested homing in X the same way and found no problem with that?

Also, another test might be helpful: In S3D try setting the Movement Override dial to different settings before doing your Y-home test. It's on the lower right of the MCP. Like set it to 50%, do your test. Set it to 150%, do your test. Maybe try really slow like 10%, or as fast as possible like 200%.

Actually you can go even faster: Send the command M220 S300 to set the speed override to 300% for example. Up to you to decide how fast you want to go to see if it has any impact on the homing behavior.

Toby
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Re: Y-Axis can't find zero right

Post by Toby » Wed Apr 23, 2014 8:30 pm

Ok i've got everything working with my being able to modify and install firmware. This is baby steps of course but i'd never done it before so i took my time. now it is reduced to c-programming in the firmware and i can go to town on that. If you still want to pursue this investigation I'm pretty confident we'll be able to locate the problem. it may take a few iterations but as long as i can program them computers are a lot dumber than me lol.

one thing is that i use marlinv24r2 which is different from your version, and unfortunately in the c files I might want to modify there are slight differences between the two. i suspect that for our purposes in locating your homing problems the differences don't matter and we can ignore them. but if we proceed we'll want to check that beforehand.

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MichaelH
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Re: Y-Axis can't find zero right

Post by MichaelH » Thu Apr 24, 2014 12:14 am

Hi Toby,
Yes I'm still investigating whats going on, I have no clue about C programming i'm not much of a help there.
Right now I work with Josh on the Heated Bed trouble.

I tried what you mentioned there is no trouble with the X-Axis works fine. The Y-Axis I tried 100 to 1000 in 100 increments and then up to 15000 in 500 increments and it stop's over and over again speed doesn't matter.
I also played with the dial in different setting same game. I confident that there is something wrong with the board.
An other thing I tried I switch the connectors from Y and X at the RAMBO and guess what Y runs fine and X has touble. :?: :?: :?:

I keep you in the loop.

Thanks again.
Michael

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MichaelH
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Re: Y-Axis can't find zero right

Post by MichaelH » Sat Apr 26, 2014 9:55 pm

Update with good news! :D

I'm up and running again. It looks like that jsc was dead on with his EMI thread in an earlier post. See here

I did some troubleshooting with Josh and his explanation made the difference, :idea: because I separated the wires and still had the same trouble but he said I need to twist them.

:!: This is Josh's post to me.
We found an issue with the Y endstop about a year ago, that manifested when a small harness change was made. Basically, when the Y stepper motor is powered, the square wave signal that the electronics use create a lot of noise, which can be transmitted to other wires; with the Y endstop wires running along the Y motor wires, that's where the noise normally went, which caused the Y endstop to "activate" sporadically, by confusing the RAMBo. We caught it quickly and fixed all the ones we knew about - yours may have been before the harness change that made the issue more apparent? Either way, yes, I think that twisting the Y endstop wires together (and maybe even the Y motor wires while you're at it) should remove the early Y endstop activation.

Thanks for all the help!
Michael

@ Toby: I'm still interested in what you can figure out with the motion control.

Toby
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Re: Y-Axis can't find zero right

Post by Toby » Sat Apr 26, 2014 10:30 pm

Very tricky. So basically the y-endstop was being activated, but as soon as the bed stopped moving the false activation signal went away? That would explain why the firmware said it wasn't activated when you queried the endstops after it had stopped.

Glad you got that fixed. Had we gone the firmware route what we would have found (eventually) is that the y-endstop was closed and then immediately opened for no apparent reason. That might have pointed to the cause, but all in all this was the faster way to go.

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