On Sunday 13 December 2015 14:39:19 Ben Potter wrote:

> > > When going through my testing for this the first time I cranked
> > > all 4 settings up to 10,000 - the problem still occurred. After I
> > > tried inverting the output I slowly stepped them back down - for
> > > my G540 I settled on 700/700/2000/2000.
> >
> > The Gecko 540 is not in the charts of our wiki, darnit. What is
> > there
>
> isn't even that fast. See:
>
> Yeah, I've thought about adding it a couple of times - but would want
> to do some more... intense testing before adding my timings there.
>
Note that those setup and hold times are relative to the riseing edge of 
the (step?) pulse, and the next line is not so specific, but I expect it 
needs to be checked by a dual trace scope for both 
conditions                                                                  .
> > <http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Stepper_Drive_Timing>
> >
> > I take it you do not have any opto-isolation in those 3 paths.  That
> > 700
>
> ns is pushing an opto's ability to switch that fast.  The BoB I used
> was all opto, and I was warned about its speed by someone (Steve
> Stallings?) on this list.

> I don't recall which channel now, but I had to remove one of 
> > them
>
> and jumper across it. I think there are probably faster opto's about,
> but what I saw on the scope just wasn't up to getting the job done.
> All the loads that
>
> > BoB see's are already isolated, so I wasn't terribly concerned about
>
> losing one stage of isolation.
>
> I have no additional opto-isolation in that path - I believe that the
> G540 uses fast opto's on all the parallel port pins (from the manual,
> I'm sure there was a post on cnczone detailed the choice of isolater
> somewhere)
>
> To clarify, the figures I gave were in the format
> DIRSETUP/DIRHOLD/STEPLEN/STEPSPACE.
>
Thanks for that , so it would have been DIRSETUP/DIRHOLD that I was 
concerned with.

> Gecko give their recommendations on timings for the drive here:
> http://www.geckodrive.com/geckodrive-step-motor-drives/g540.html
>
> Those indicate 2000 nS for '0' on-time, 1000 nS for '1' on-time, 200
> nS for direction setup and hold. So it looks like I'm just within
> their recommendations on step length.

And that gives you far finer tools to tune with than software stepping 
ever will.  There may better interfaces than the 5i25, but for us 
stepper people, its the cats meow.  Not bulletproof on its inputs, I 
didn't have a good enough grounding setup wrapped around my G0704, and 
apparently blew the input I was using for a probe.

I don't know as Peter could tell me which chip to replace to rescue it. I 
AM a C.E.T. and in my dayjob before I retired in 2002/6/30, I could have 
done it easily, but at 81, my hands aren't as steady as they once were.

> I'm hooked up to a 5i25 instead of a parport though.
>
> > All my drivers are just 3 types, 2M542's, 2m860 and Pico pwm-servo's
> > for 2 of the 3 spindles at my place.  And I'm not pushing any of
> > them that
>
> fast.  But because of that slow BoB, ISTR I am running dir setup and
> dir hold about 1.5x longer than the wiki shows for the LeadShines.  So
> my experience is not > with a wide range of drivers, but I will no
> longer consider opto-isolated BoB's because everything I have is
> already isolated. Best BoB IMO, 10ns response times, but its been
> taken down, is the cnc4pc C1G that I have 2 of.  What he > is selling
> now is NOT the versions I have. Everything on mine has an led tally,
> which simplifies troubleshooting considerably.
>
> > Also, generally, where you have the choice of commonizing the +
> > terminal
>
> of a driver loads input, you are far better off doing that, and having
> the BoB pull it to ground as the pulldown in most TTL circuits is much
> more robust. > Having the reverse setup, where the - terminals are
> commonized, is generally NOT a good idea due to a lesser amount of
> pullup power to light up the opto in the drivers own input.
>
> I've gone to using mesa cards for pretty much all my interface as far
> as possible, I've had odd issues with Gecko and Leadshine drives, I've
> managed to work around them so far. The industrial drives I have used
> have generally behaved better. Since the machines I'm converting seem
> to be getting larger, I thankfully get to use servos more than
> steppers these days.
>
> The one I haven't tried yet, but would be curious to see if anyone has
> comments on is the Argon or Ion from Granite Devices.
>
> Ben

I can't comment based on experience with them so I won't, Ben.  Other 
than to say that 98% of the opto stuff out there, will need a pulse in 
excess of 1 microsecond on, and often pushing 2 u-s to turn off. I 
understand there are some Gas based optos about, but they'd have a 
serious effect on a BoB's price.  One could turn a $15 BoB into a $100 
BoB pretty fast.

However, one must bear in mind that when looking at it with a scope, we 
are watching the voltage, and in opto stuff, voltage doesn't mean near 
as much as actually measuring the current.  Why?  Because when the 
driving led in the opto goes out, which it might do at 1.85 volts or   
as high as 2.4 volts, the load is gone, leaving the voltage to decay 
toward (which ever rail its headed for) at a very leasurely rate.

Thats a fancy, CMA way to say the scope is lieing to you.  So I tend to 
look at the decay with an eye toward seeing if I can define that point 
where the down (up?)ward curve changes to a slower rate, then make 
the "on time" timing measurements to that point. That can be a difficult 
point to define even for me, and I've "had a scope probe in one hand" 
for 64 years. 64 years ago it was a 5mhz Hickock, today I have 100MHZ 
dual trace analog, and 200mhz dual trace digitals to go poking around 
with.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Some mill pix are at:
Genes Web page <http://geneslinuxbox.net:6309/gene/GO704-pix>

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