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strange intermittent problem
« on: August 24, 2011, 06:53:51 AM »

I've just run my new lathe retrofit for the first time and there seems to be a problem
this is not the first machine I hve run Mach 3 on..  so I thought I knew what I was doing (famous last words !)

25Khz kernel  on a 3 gHz pentium 4 desktop machine with 1 Gig of ram running xp
set to always on, with no anti virus, network connection etc.

generic 5 axis breakout with CW8040 drivers on 4A steppers at 75Volts

when jogging at full speed on full travel of the axis as a test, 19 times out of 20 no problem at all
but every now and again the axis stops and the same kind of noise as a stalled motor is heard.

If this was on one axis, i would suspect a mechanical problem, but it happens on boths axis at about the same frequency at different places
if I take my finger off the jog momentarily, and reapply, the axis moves normally again

I have checked stuff like power supply voltages under load, and I only lose a volt or two

I have tried changing the step and direction pulse lengths, and I have tries increasing the kernel speed.

I have run the axis backwards and forwards by hand and they feel nice and smooth

any thoughts as to what to try next ?

Re: strange intermittent problem
« Reply #1 on: August 24, 2011, 07:26:35 AM »
Your motor tuning might be right at the critical point.
De-tune them by about 10-20% and see if it helps.
Re: strange intermittent problem
« Reply #2 on: August 24, 2011, 08:23:15 AM »
Thanks Russ,

I tried at 150%  current speed and 50% current speed and the symptoms were the same..

I went through the full optimisation steps and the problem is the same.

I have to go out for a while, but when I get back I will try without microstepping (set to 1/5 currently)

Its odd that it affects both axis equally, and with virtually no load on the axis

I may try a scope on the output of the breakout board, see if it changes during the stall..

Its probably something very simple


Re: strange intermittent problem
« Reply #3 on: August 24, 2011, 09:38:53 AM »
Could well be mid-band resonance....
Ray L.