On Friday 07 December 2012 11:04:27 Steve Stallings did opine: > .... normally a top poster here, but will try to insert > my comments in a rational place below..... > > > -----Original Message----- > > From: Michael Haberler [mailto:[email protected]] > > Sent: Friday, December 07, 2012 3:22 AM > > To: EMC developers > > Subject: Re: [Emc-developers] latency histogram comp > > > > Jon, > > > > Am 07.12.2012 um 04:37 schrieb Jon Elson: > > > Michael Haberler wrote: > > >> sorry for what maybe sounds like a dumb question, but > > > > having read the Proctor/Shackleford paper on the influence of > > jitter on steppers which basically say: "all it causes is a > > loss of torque on the order of 10%" (given the figures at the > > time the paper was written), > > > > > That's a bit dismissive of Fred and/or Will, a major RT > > > > stutter will > > > > > cause more > > > than a 10% loss of torque. > > > > this is the way I understood the gist of the paper, and I > > found that a quite interesting summary > > > > not being a native speaker: can you fill me in what you > > consider "dismissive" about that? > > Not to address the issue of "dismissive" or not, but just to > consider the information provided.... > > The paper being referenced can be found here: > > http://www.nist.gov/manuscript-publication-search.cfm?pub_id=824455 > > In the data cited in this paper the motor speed was 15 revolutions > per second (900 RPM) with the motor running in half step mode. This > required 6000 steps per second or a 166.66 microsecond step period. > The stated jitter for the results of less than 10% torque loss > (actually 7.6%) was 3.6 microseconds. This is a jitter of 2.16%, > so the loss of torque in percent is approximately 3.5 times the > percentage of jitter timing. I have not checked out the derivation > of the formulas in the paper, so I will use this as a rule for > rough approximation. > > Many systems used by LinuxCNC and Mach3 users push the timing much > harder to try to get higher speeds. Jitter of 25% is not uncommon > in some software only schemes. This can result in a torque loss > of about 87.5% which is enough to produce results like those Jon > cited in his Sherline experiments. > > The motor in the NIST test case was run at a speed that allowed the > motor to produce 50% of its holding torque. This is a reasonable value > for industrial use. I only wish we could get most users of LinuxCNC > and Mach3 to accept such assumptions when setting up their machines. > > Regards, > Steve Stallings > www.PMDX.com > This is quite informative Steve, thanks. It also sends a rather powerful message that we really ought to consider that step generation is a hardware job. Then that boils down to who has the needed number of step generators on their boards, and at what price. And how do they interface. The atom boards are only 1 slot pci-e boards, so we have to choose carefully.
So, who does make suitable 2 and 4 channel step generation boards? Neither version of the smooth stepper would appear to be usable with linuxcnc, so what is out there? > > > I did an experiment a LONG time ago when I > > > > > > developed the first hardware step generator for EMC(1) in > > > > 2001. I was able > > > > > to improve the top speed of a Sherline mill by a factor of > > > > about 5 by > > > > > creating much smoother step pulse trains than the software > > > > step generator. > > > > > I don't know the latency that machine had, but it was not terrible. > > > > what I'd be interested in: was that a consequence of the > > capability to generate more continuous frequencies or a > > consequence of less jitter (which was the point in the > > original question)? > > > > -m > > > > > Jon > > ------------------------------------------------------------------------ > ------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free > Trial Remotely access PCs and mobile devices and provide instant > support Improve your efficiency, and focus on delivering more value-add > services Discover what IT Professionals Know. Rescue delivers > http://p.sf.net/sfu/logmein_12329d2d > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! Class, that's the only thing that counts in life. Class. Without class and style, a man's a bum; he might as well be dead. -- "Bugsy" Siegel I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
