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Skipping steps

Posted by martenjacobs 
Skipping steps
May 11, 2013 02:35AM
Hi all,

This is my first post on this forum so please be patient with me smiling smiley.
I've built a Prusa Mendel, it's sort of a i2/i1 hybrid, as I understand the i2 has no lower thickplate and mine has, and also some of the rods in my build were not the exact sizes as mentioned in the assembly instructions, but I made it work, I'm also using an aluminium heated bed, which did not stick at all at first, but thanks to the magic ABS juice I found on this forum it does now (I may be upgrading to a glass bed at a later stage because this one is not completely flat, but it's fine for now). I've even added cooling to the PEEK part of my J-Head to ensure it stays rigid.
So now it's now running rather nicely on a Sanguinololu with the Repetier firmware.

There is, however, one issue left that's keeping me from printing anything other than a jumbled heap of ABS: when attempting to print, the X and Y axes start fine enough but very soon they start veering off. For a second or two, there is no movement from the axes, but the firmware seems to be unaware of this, throwing off the position. After a while I've even noticed the axis can start hitting the sides of the machine, causing the belts to jump, which is unpleasant. I've already done some things to fix it, but have been unsuccessful.
My motors are all Kysan 42BYGH4803 (http://www.kysanelectronics.com/graphics/1124030.pdf), so according to the Sanguinololu page on the wiki, my Vref should be 0,6V

In order, I tried:
    - Improving the Vref setting on the Pololus (they're now all between 0,598 and 0,602 on my cheap multimeter, which is about the best I can do with the tools I currently have)
    - Lowering the microstepping from 1/16th (which was the maximum for the Sanguinololu) to 1/8th
    - Lowering the feed rate on both axes (to 200mm/s)
    - Turning off microstepping altogether (this caused the machine to vibrate way more than it did before)
    - Lowering the feed rate even more (to 40mm/s)
    - Lowering the acceleration (to something like 10mm/s^2)

Can anyone tell me what's the next thing I can try?

Thanks in advance!

Re: Skipping steps
May 11, 2013 05:48AM
0.6V seems too high for Vref unless you have heatsinks and a fan on the Pololus. They may be getting too hot and shutting down until they cool again.

Try 0.4V.

Edited 1 time(s). Last edit at 05/11/2013 12:53PM by nophead.

Re: Skipping steps
May 12, 2013 05:54AM
@nophead: Thanks, that made all the difference!
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