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). 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
