Thanks for all the suggestions. No solution yet but a quick update... The signal from the direction pin checked out ok on the multimeter so it is definitely a hardware issue. I have so far checked for bad connections leading up to the PCB and off it to the motor and they are ok.
Next step is to take the PCB out and check those connections. The driver is a "SLA7051M-LF871" chip by the way. Progress was slowed somewhat when I foolishly switched the connectors from the Y motor to the Z motor and caused a small explosion! I was thinking I could isolate the problem to either the driver board or the motor, but only managed to blow up the driver chip on the Y Board :( It turns out the 'slightly differently spec'd motors have quite different pin mappings... well at least as they have been mapped out on this DIY connector. So one driver chip down and two more on the way. This CNC stuff is actually quite fun! Karl On Mar 30, 2010, at 5:25 AM, John Harris wrote: > Hi, > Under some circumstances this effect can be produced by one > motor winding connection not being good at the driver end of the motor > cable. Usually with a long (2 mtr) cable. Can also be due to one > output of > the driver unit being bad. With power off, use an ohmmeter to check > the > winding resistance at the motor end off the cable, then look for > similar > resistance at the output pins of the driver unit, and the output > pins of the > driver ICs. If that looks good, with power on and the motor running > look > with a scope at the waveforms on all four driver outputs. The two > outputs > for one winding are different, but one output on one winding should > be the > same as one output on the other winding, and the other two should also > match. > > Also an open circuit Direction signal, with the open at the breakout > board > end of the cable can produce similar effects as suggested below. > > ----- Original Message ----- > From: "Slavko Kocjancic" <esla...@gmail.com> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net > > > Sent: Tuesday, March 30, 2010 2:23 AM > Subject: Re: [Emc-users] Random Direction Changes > > >> darcys...@gmail.com pravi: >>> Hi all, >>> >>> I am experiencing some odd direction changes on a home-brew CNC >>> machine that I have on loan. >>> The machine was apparently purchased off ebay, and all the >>> settings I >>> dug out from data sheets for the driver chips and motors. >>> >>> X and Y are working well, but Z (which has a similarly spec'ed but >>> different motor from the other two) decides to change direction at >>> random. >>> The basic behavior is that when you push the jog button in a certain >>> direction you don't know which direction it will go. >>> It will maintain it's course in that direction, but when releasing >>> the >>> button and pressing it again, it will again choose a random >>> direction. >>> Thus the problem it is very easy to reproduce. >>> >>> I am interested to hear what you think this problem may be caused >>> by? >>> I have yet to pull out the oscilloscope, but being a relative >>> newcomer >>> I wanted to ask for advise on how best to debug this problem. >>> >>> I should add that I did have this CNC set up briefly on Mach3, and >>> encountered the same issue. >>> >>> Thanks in advance, >>> >> Just check the wires again. That can be caused by bad connection of >> DIR >> signal or even replaced dir/step signal or shorted together. If you >> don't have scope then just use earphone. Connect earphone trought 10k >> resistor to direction signal and ground. You should hear nothing when >> motor moves. But must hear click when you change direction. On the >> step >> pin you should hear clear tone without clicking. That's works even >> betterthan scope!. As all interrupts are heard as clicking in steady >> signal. On scope is very easy to miss that glitch. >> >> ------------------------------------------------------------------------------ >> Download Intel® Parallel Studio Eval >> Try the new software tools for yourself. Speed compiling, find bugs >> proactively, and fine-tune applications for parallel performance. >> See why Intel Parallel Studio got high marks during beta. >> http://p.sf.net/sfu/intel-sw-dev >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > > > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
