On Sun, 2012-12-16 at 01:39 -0500, cogoman wrote: > On 12/15/2012 04:23 PM, Ben Potter wrote: > > I've got a machine with much the same limit (1200 line) - which is somewhat > > frustrating at times. I couldn't figure out a way to (easily and cheaply) > > convert it over to linuxcnc without replacing the existing drives and > > resolvers - which made it a rather more time consuming and expensive task > > than I was willing to undertake. Oddly enough, there was a post from Tim > > James earlier today about a conversion chip which looks like it may allow me > > to use the original resolvers - bringing the pain of conversion down to > > tolerable levels. The other option would be to upgrade the controller to a > > TNC 151 or 155 - but they seem to be rather rare these days. > One option on the wiki (but well hidden) is a 3 channel resolver to > quadrature converter using an arduino and a power op-amp. It uses a > 2KHz excitation frequency, while the Pico Systems board can use up to > 10KHz. The Pico board goes up to 60000RPM, while the arduino probably > can't go near that. Still if it can handle 6000 RPM that would be > pretty good. The Pico board gives 4096 counts per revolution versus 1024 > for the arduino. The aduino can serve 3 channels at one time. If the > new 32 bit arm arduino can do the same sort of thing, it should be able > to keep up with a 10KHz excitation signal, but that would require a > significant amount of dev time. > Here is a link to the wiki entry. > > http://wiki.linuxcnc.org/cgi-bin/wiki.pl?ResolverToQuadratureConverter
Interesting idea and gives you three channels. However there is another issue here. Basic resolution adequate for servo control. The good news is that the resolver is probably geared to the servo shaft maybe a 3:1. So, making further assumptions.... 2:1 gearing to the ballscrew and 4 tpi ballscrew gives 1024 * 3 * 2 * 4 cpi. = ~25000 cpi. If true that is not bad. I've worked with systems as low a ~5000 cpi and they were a bit iffy on control. Realize that 5000 cpi will probably yield control to sightly better than 0.001" which is OK for most hobby machines. Anything better is pure gravy. In brief having lots of counts makes the pid happy. Hang in there. (enough rambling for one morning). Dave > I found it by searching yahoo with: > > site:linuxcnc.org arduino > > and then looking for resolver to quadrature converter. > > If you decide to try this, you might try breadboarding the circuit > using the ardweeny from the makershed > > http://www.makershed.com/product_p/mksb012.htm > > and the lm272, but you would probably save in the long run by just > building it the way the wiki page shows. > > ***** thanks Andy for the documentation on this! ***** > > > As to the motherboards, I was just referring to how a motherboard > that many find works extremely well, sometimes doesn't work well for > another. I would expect a reasonable choice of motherboards with 2 > different models should be guaranteed to get one that will work well for > LinuxCNC. > I've heard of Monday and Friday cars. I wonder if there are Monday > and Friday electronics. I was looking at some android cell phones that > my wife and I are getting, and when I sorted the comments by date, the > people who commented Dec 10 of this year seemed to have phones that > locked up often. Going back just 3 days from that and everybody seems > to be gushing about how good they are. I hope we don't get Monday or > Friday phones! > > > ------------------------------------------------------------------------------ > 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-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ 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-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
