On Wednesday 15 July 2015 02:22:06 Marius Alksnys wrote: > On 07/15/2015 08:59 AM, Gene Heskett wrote: > > Trying to learn something here, I see the use of several of the ddt > > modules, which appear to be used for detecting the slope, or change > > velocity, its output. > > > :) No, these ddt and hypot are not needed here. They where used to > : trace > > velocity - just for testing, derived from TP testing config, which > tracked max acceleration of each axis and had nice side panel: > http://wiki.linuxcnc.org/cgi-bin/wiki.pl?NewTrajectoryControl
Lots of stuff there I'll have to study. Hopefully that will be in the printable pdf's at some point after 2.8.x is declared usable for all. I had to switch to it because the 2.6.x stuff had turned into a crashomatic on both of my atom board. I've found that the 2.8.0-pre's have been usable, and rock solid stable. I do have a bit of trickery in the hal for the spindle servo, a bias so the creep speeds were similar in both directions, but stop is off, no servo so it coasts. Yesterday, when I was trimming that sleeves in .05mm increments, hoping I didn't end up making 2 pieces out of it by cutting thru the sides of the 2 thru holes for its mounting bolts, that I could click stop then get a much faster stop by reclicking the fwd button, but its creep speed (about 5 rpm) was backwards! Stop it again, and click fwd a second time, and its normal, creeps fwd. Unforch, I think that also wrote a fini to that plastic drive timing pulley, so I find I now have to ask for 500, get about 475 that drops to 350 when shaving .05mm of alu from a nominally 38mm bore. But I have not found a timing pulley maker that can make for that old style belt, that number of teeth and a 9mm shaft bore, that doesn't want $200 for it. I have looked at the other choices in smaller machines, and NONE of them have drive parts capable of surviving a full cut of steel at their rated and advertised swing. Or the horsepower to do the cut at that swing. Needing some fresh brushes for the toy mill, I just bought 3 belts and 5 more of those pulleys along with some QC tool holders so I can have more tools premounted, all from LMS. I have plans to ditch the jackshaft and the backgear, and use a polygroove pulley about 6" in diameter directly on the rear of the spindle. Which should result in a machine that can actually remove half a mm of metal from any diameter the toolpost can reach. This S.O.B., as shipped doesn't have the power or drive to cut steel above .75" in diameter. So the 7" swing they gave it is pure bull shit. With sharp enough tooling, it might be able to cut balsa at a 3.5" radii, but I'd have to see it do it. Yeah, I am P.O.ed and tired of replacing $4.65 bits of plastic because I can't buy a suitable metal version... > > OTOH, I haven't any experience with velocity driven servo's, and if > > I were to do a servo driven machine, I would automatically use > > position desired, and position feedback to achieve the desired > > result, a near vanishing position error. > > > > Where can I learn how a velocity servo achieves the positioning > > accuracy that allows it to do as good, or perhaps even better, > > working accuracy compared to a position servo? Surely there is a > > tut on this? > > Yes, having velocity and position loops increases trajectory following > accuracy and eases PID tuning. If you have only torque or PWM mode > servo amplifiers, then you can create velocity pid in LinuxCNC. It > should track axis velocity (you can use encoder-velocity output or ddt > here), directly control the amplifier and get command from position > PID. Velocity PID might have only Igain non-zero. > This helps a lot in certain setups. So you were subbing the ddt outputs for an assumed perfect encoder on the axis output. Makes sense as a troubleshooting tool. > What I found: > http://www.anderswallin.net/2008/04/x-axis-test/ > http://gnipsel.com/linuxcnc/tuning/servo.html > http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Tuning_LinuxCNC/HAL_PID_Loops > http://wiki.linuxcnc.org/cgi-bin/wiki.pl?PiD These I have seen & studied before and have arrived at PID settings that seem to work. But I'd be the first to say they may not be perfected. Thank you Marius. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Don't Limit Your Business. Reach for the Cloud. GigeNET's Cloud Solutions provide you with the tools and support that you need to offload your IT needs and focus on growing your business. Configured For All Businesses. Start Your Cloud Today. https://www.gigenetcloud.com/ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
