Na 17.9.2010 10:53, Andy Pugh je pisal: > On 17 September 2010 09:16, Slavko Kocjancic<[email protected]> wrote: > >> but with EMC that wil be like that 250,250,250,250, (new servo thread >> calc), 245, 245, 245, 245,.... >> I thinking to put stepgen in microcontroller as finding good PC with >> lattency under 15us is not easy. > The Intel Atom mini-ITX boards run at 8uS from a LiveCD installation, > and cost $75 > >> So base period under 20uS is not likely >> on PC but for $2 microcontroller the 5us is easy reach. > In practice, it is very rarely a problem. Loaded stepper motors very > rarely manage more than 2000rpm for reasons unrelated to drive pulse > smoothness. (at 8x microstepping that is a 20uS pulse time). > > If you want finer granularity then both the Pico and Mesa systems > offer that. The Mesa 7i43 plugs into a parallel port and offers 48 IO > pins and hardware stepgen at (IIRC) MHz resolution. More expensive > than your $2 uController at $79, but then it is already supported by > EMC2 so will "Just Work". The same is true of the Pico PPMC cards, I > believe, but I am less familiar with them. > > However, this still doesn't really help with the issue that seems to > be bugging you, that the step rate only change every Servo Period. I > am afraid that is not likely to be easy to change, as the floating > point motion calculations take time, and can only be run in the slow > thread. > > However, why not start off with your system running off the P-Port and > see if there is a genuine issue? My axes max out at somewhere around > 30mm/sec for reasons related to voltage and motor inductance, so > <calculate> that is 720rpm from the motors, or a minimum step time of > 100uS at x4 microstepping. I do actually have a 7i43 card so step > timing granularity is not an issue and did not see any improvement in > rapid speed compared to the p-port only system (I made the switch to > get more IO pins) > I had 3axis machine and work happy with 1000mm/min. But if I drive same motor/driver/machine with 555 timer and translator I can get over 2500mm/min. So EMC2 probably has too much jitter. I had 16us jitter and base at 25us. I can go lower bith base up to 21us and stall computer at 20us. As this is not production machine but just for hobby I don't want to buy new computer for that. I just pick LiveCD and measure my scrapjunk PC computers (aprox 10 of them) and pick best one. It's HP NX9005 laptop. It has some SMI related problem (probably problem with dead battery as problem dissapear when I get battery out.) So I got one (out of 10) with latency under 20us. All other are below 100us so good for servo and one is completly unusable with 6ms latency at every mouse move. ?!?
I looking to mesa for $79 and I can live with that but they doesn't support quadrature output as all my drives are not STEP/DIR but are phase drives or quadrature. And I like to complete EMC2 in way as is. FREE! Emc is Free so the some board should be free too. The one parallel port is just on limit for many machines. there are no schematics for some expander on EMC2 pages. Just commercial one. That is not right. If I complete the board then will be available with least a hex code if not source. ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
