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Author Topic: Stepper motors move jerky and weird  (Read 403 times)

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Stepper motors move jerky and weird
« on: May 11, 2019, 10:07:05 AM »
Hi you all,
ive just converted my mill to cnc and tried starting to use it with mach3 and I dont have any prior experience with mach3.
So I want to tell you what happened:
The first thing ive done is, using a pcie db25 card, connected an leadshine MX3660 to my normal desktop pc (i7 4770k and R9 390, so nothing special) and installing Windows 7 32 bit on a seperate partition on it.
This worked perfectly well (as perfect as can be).
As thats my primary pc and I still want to use it while cncing, ive bought a secondary pc for the cnc (xeon 1220, Quadro 2000, ecc ram) and threw the 32bit windows 7 drive and the pcie db25 card in there. This also worked to the extend of being able to connect the MX3660, but when using them the problem started:
They not only whined unbearably but they also didnt really move as I wanted them to.
To illustrate this ive made this video of the issue:
https://youtu.be/gkuvDi-UIqc
I have also scoped the outputs of the motor driver, files in the attachment.
If it helpes I can also scope the parallel port while plugged in into both pcs.

So the question:
Does anyone how to solve the issue (exept for swapping out my main with my secondary pc)?
Re: Stepper motors move jerky and weird
« Reply #1 on: May 11, 2019, 02:40:45 PM »
Hi,
while interesting to look at the motor traces are no going to help you diagnose the fault.

Even traces of the step input signals will probably not help a great deal. The timing jitter of Machs parallel port
is often 4us or so. Thus even a 'good' pulse train is going to have jitter that would render the trace un-readable.
There are scopes that record histograms of the signal under test and would be ideal but they are specialist devices
and unlikely that you have one.

Machs parallel port driver is code that runs at  kernel level 0 within the PC's CPU. Windows never anticipated that
the PC would be used that way, and the computing world looked on in amazement when Art Fennerty wrote it, all swearing
that 'its not possible'.

I think what you have happening is that some PC's run Machs parallel port well and others do not. Some old XP clunker
will do a good job whereas a powerful PC with 'muscles on it muscles' wont run at all.......and no real way to tell.
Once upon a time there was list of things you could do to improve your PC for running the parallel port, it was quite
extensive, about 40 items and took several hours to work through.  I haven't seen or heard of it for ages.

This variability of performance (of the parallel port) on different PC's is one of the drawbacks of the parallel port, and has been
with us from the get go. It must be said though, provided you were prepared to try several PC's to get a good one that the
parallel port works pretty well and for free. It was that fact that allowed Mach3 to become as popular as it has with such a loyal
user base.

One solution that you might consider is to buy an external motion controller like an Ethernet SmoothStepper. An external
controller removes from the PC the need to generate high accuracy pulse streams for which a PC's CPU is poorly suited.
An external controller would allow use of 64 (or 32) bit Windows up to and including Windows10, you could use a laptop
whereas the parallel port required a desktop. Mach running through an external motion controller is very very much
less subject to stalling or stuttering due to extraneous software/services running on the PC.

If you do want to consider an external motion controller don't buy Chinese junk, they often don't work at all, or work well
even if they work, and you wont get any manufacturers support.

Craig
My wife left with my best friend...
     and I miss him!
Re: Stepper motors move jerky and weird
« Reply #2 on: May 12, 2019, 11:58:46 AM »
Thanks a lot, if I went with an external motion controller, could you recommend one?
My wife left with my best friend...
     and I miss him!