On Monday 18 February 2013 14:14:35 John Stewart did opine: > Gene; > > I purchased a tachometer from that bay store, and plotted the effects of > the pwmgen input value. > > I was very surprised to find the results linear; I wrote up my stuff on > my blog - http://cnc-for-model-engineers.blogspot.com > > It was linear, and when I request a spindle speed, it usually comes out > within 5%, many times within less than 1% now that it is calibrated > properly. > > I generally put a 2 second wait into my GCODE, because it takes a bit > less than that to max the spindle from full stop. > > (I'd give you a direct link, etc, but I can't get to the web this week > very well. (i.e., it times out) but email works.) > > JohnS. > Stuck in Turks and Cacos, > wishing I was in my workshop! Apparently, in the 250 watt motor controller (no schematics are available) in the OEM mini-lathe, the pot arm connection goes straight to the feedback summing junction in the circuit, presumably using the 10k pot as a build- out resistor, a voltage to current converter IOW.
With the LF357's output impedance likely under 10 ohms since its a gain of 1 voltage follower, it overpowers the sum junction and becomes almost an on-off switch that the PID module cannot linearize. Since the pot I took out was 10k, I took a SWAG and added a 10k to the C6 by cutting the trace to the output connector from the LF357 and cleaned up the trace enough to solder the 10k to it. First 10k value worked so well I never tried anything different. From the gui, clicking the CW start button on causes the motor to creep & jerk along slowly at about 1 rpm, and any following clicks on the plus or minus buttons run it up or down by 100 rpms/click. Above 200 revs its extremely stiff, a pony brake made of an old leather belt can pull it down to perhaps 190 rpm by the time I can smell hot leather from the belt. I don't think Arturo ever dreamed his C6 would be used inside the feedback loop of a PID controller though. :( 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! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> Beware of computerized fortune-tellers! I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ The Go Parallel Website, sponsored by Intel - in partnership with Geeknet, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials, tech docs, whitepapers, evaluation guides, and opinion stories. Check out the most recent posts - join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
