1 Topic by Rincewind

  • Rincewind
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Topic: On motors skipping steps - another insight

Hi all,

I wanted to share the experience I recently had with a motor skipping steps/layers shifting.

I have a solidoodle 2 that worked perfectly when attached to a computer, everything calibrated, smooth action. When attached to a different computer (a tablet, through a USB OTG interface), the print would work fine for a while, and then start skipping steps (in the Y direction, in my case). And they were not one or two steps either, sometimes a complete movement in the Y would be ignored and for a diagonal move, only the X component would be executed.

It took me some time to track down the problem: it was not mechanical, it was not the serial communication... In the end it turned out that the problem was with the USB voltage.

Apparently, the OTG interface had a voltage supply a bit higher than 5V, and this was shifting the references throughout the Sanguinololu board. In fact, the Y trimpot voltage was 40mV higher while connected to the tablet than when connected to the PC.

In the end, I solved the problem at the root by cutting the 5V supply from the USB as suggested here.

I think that adjusting the trimpots would have also worked, but that would have meant a readjustment every time I changed the computer driving the SD, which I didn't want.

This is NOT the only and not even the most common reason for layer shifting, but I think it was worth sharing because it was a tricky problem. And I guess the take-home message is: the trimpot voltages can change when connecting the Solidoodle to a different computer.

2 Reply by op7ical

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Re: On motors skipping steps - another insight

This is very good to know.  We should compile a list of problems that cause layer shifting / skipping.

So far, I know of:
-Belt tension too tight or too loose, or uneven
-Inadequate lubrication for guide rods
-Set screws on pulley collars loose
-Stepper drivers overheating; require cooling
-Trimpot voltages incorrect (either stock, or caused by USB voltage variations)
-USB communication dropouts due to physical connection, software, or baud rate mismatch

3 Reply by jjcuff1

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Re: On motors skipping steps - another insight

The USB issue and sleep mode (which I turned off in my laptop) I think causes some. When I hit space to wake up (even though machine is still running and HDD is set to no sleep in MAC) the printer still pauses then  resumes. I bet this could easily cause a mis step

I also noticed you have to set the trim pots with the PSU power plugged in NOT JUST the USB power I found out it makes a big difference.

And I also noticed after all my fixes above, I still had shifts. I realized I might have a small clog in the nozzle. I heated up retracted the filament then pushed out burned plastic with a guitar string. And the next print when fine. I think the clog was causing the filament to come out at odd angles and either shift or drag across layers especially small ones

Simple fixed but immediate difference.

SD2 owner- Surestepr, filament holder,QUBD servo and heaters, glass bed
Print for fun and for parts for my sports cars
current car is 88 IROC

4 Reply by Rincewind

  • Rincewind
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Re: On motors skipping steps - another insight

op7ical wrote:

This is very good to know.  We should compile a list of problems that cause layer shifting / skipping.

Thanks for the list. I think it is very important. I was also thinking about something along these lines

-USB communication dropouts due to physical connection, software, or baud rate mismatch

This I'm not sure. A baud rate mismatch would just make the printer fail connecting, and an error in the serial communication would be detected by the firmware with a line number of checksum mismatch.

I don't think it can cause skipping steps. Or do you have a different experience?

5 Reply by op7ical

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Re: On motors skipping steps - another insight

This I'm not sure. A baud rate mismatch would just make the printer fail connecting, and an error in the serial communication would be detected by the firmware with a line number of checksum mismatch.
I don't think it can cause skipping steps. Or do you have a different experience?

That's true, I guess it shouldn't skip from that error.  However, I have accidentally interrupted power to the machine once, and the print was shifted by a distance proportional to the time in which it lost power.  This is a different problem, but it may be some use in rare occurrences.

6 Reply by Rincewind

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Re: On motors skipping steps - another insight

op7ical wrote:

That's true, I guess it shouldn't skip from that error.  However, I have accidentally interrupted power to the machine once, and the print was shifted by a distance proportional to the time in which it lost power.  This is a different problem, but it may be some use in rare occurrences.

Ah, actually this situation is very interesting because there is a very logical explanation for it: the electronics stays powered by the USB but the motors don't move because they need the 12V. So from a firmware point of view, the machine is still printing fine, except it's not.

7 Reply by Rincewind

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Re: On motors skipping steps - another insight

I created a wiki page on this: http://www.soliwiki.com/Motor_skipping_steps

8 Reply by tealvince

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Re: On motors skipping steps - another insight

Rincewind wrote:

I created a wiki page on this: http://www.soliwiki.com/Motor_skipping_steps

Excellent!  And should the procedure and circumstances where one might want to isolate the Sanginololu from the USB power be mentioned here as well?

9 Reply by Rincewind

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Re: On motors skipping steps - another insight

tealvince wrote:
Rincewind wrote:

I created a wiki page on this: http://www.soliwiki.com/Motor_skipping_steps

Excellent!  And should the procedure and circumstances where one might want to isolate the Sanginololu from the USB power be mentioned here as well?

Good point! I will add it (as soon as I finish compiling the list of compatible hardware I'm working on ATM smile )

10 Reply by jefferysanders

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Re: On motors skipping steps - another insight

I've waited long enough to do this myself...for me the issue potentially kills my connection to the printer anytime someone changes the ceiling fan speed in my office...derp fail.  I never thought about it just throwing errors in the stepping, but now you've brought that effect to my attention, I'll just fix that trace before my next print...a easy fix.

11 Reply by lawsy

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Re: On motors skipping steps - another insight

I've had y shifting issues on and off when running the printer from the Pengpod. Tonight I've severed the 5V line from the USB as per the link (option 2) and so far the test print is ok.

Thanks to all for posting the resources here and on the wiki.

lawsy's Website