You can only *properly* diagnose PWM signal with an oscilloscope or a
digital analyser. The PWM ramp-up or ramp-down may be really short (0.5s)
for the DMM to notice.
On Fri, Sep 19, 2008 at 4:47 AM, Sebastian Kuzminsky <[EMAIL PROTECTED]>wrote:
> Eric H. Johnson wrote:
> > The run-away problem seems to be licked, at least for relatively slow
> speeds. I am, however, still getting following errors at higher velocities.
> These start to occur at about 3IPS. The motors should max out at about 12
> IPS. Max step rate on the motors should be 20 RPS * 200 steps per revolution
> * 16 micro-steps per step, or 64000 steps per second. At 3 IPS, it should be
> about 16000 steps per second.
>
> Yay! Thanks for the debugging work, Eric!
>
> Is this with the latest stepgen.c that I posted earlier today?
>
>
> > I have base period set to 25000 nsec, and servo period set to 200000
> nsec.
> >
> > I assume the following error results from position-fb getting too far
> behind position-cmd, but I do not know what needs to be done to resolve this
> problem.
>
> What are you doing in the base thread? It shouldnt be needed for this
> setup, as I understand it.
>
> I'm not sure how to approach this following problem. Matt Shaver
> reported a similar problem... I think Steve found a bug in Matt's
> stepgen config, but I'm not sure if fixing that bug fixed his following
> error.
>
> The wiki FollowingError page,
> <http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Following_Error>, suggests
> that following errors with steppers might be because ferror or
> min_ferror are too low, or maxaccel or maxvel might be too high. (BTW,
> that page has a broken picture on it.)
>
> How does emc2 decide that a following error is happening?
>
> Is it true that when emc2 interprets g-code, it makes a long array of
> points (in whatever axis-space the machine operates) and feeds each set
> of coordinates to the position-cmd pins on the controllers for the
> various axes?
>
>
> > Secondly, now that I am back to it, the PWM does not seem to be changing.
> It is either off, or what seems to be close to full on. My meter reads
> either 0V or 3.16V. I did find that a mirror must have gotten bumped,
> resulting in apparently low output from the laser. Following a beam
> alignment, laser power does look to be close to full on.
> >
> > Any ideas on how to troubleshoot this is appreciated.
>
> I think measuring a PWM signal with a voltmeter isnt reliable; it
> depends on how fast the meter is. Isn't there some simple RC circuit
> that can be placed between the PWM pin and ground to make a
> duty-cycle-controller voltage that can be reliably measured with a DMM?
> I really dont know but I think I read something like that...
>
>
> --
> Sebastian Kuzminsky
> Theo: "Julian? I haven't seen you in twenty years. You look good.
> The picture the police have of you doesn't do you justice."
> Julian: "What do the police know about justice?"
>
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