On Friday 07 December 2012 12:24:15 EBo did opine: > On Dec 7 2012 9:35 AM, Gene Heskett wrote: > > 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 disagree. You can get better/faster results in a given piece of > hardware, but for low speed general applications stepgen is perfectly > fine. I would ask the question how fast can we realistically expect the > general solution to work, and how much can the specialized hardware buy > me (for a given cost). > Those too are valid questions, with very iffy answers for the hobbiest like me. The improvement probably would be appreciated, but in nearly 10 years of having the basic machinery, I have only re-couped maybe 10% of their original cost. And those jobs were so simple I could have cranked them out with hand cranks.
> EBo -- > > ------------------------------------------------------------------------ > ------ 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! Don't abandon hope. Your Captain Midnight decoder ring arrives tomorrow. 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
