On Saturday, February 21, 2015 10:22:15 AM Erik Christiansen wrote: > On 21.02.15 09:27, Gene Heskett wrote: > > The disadvantages are that they will continuously burn from 25% to > > 50% of their running power even if being driven by smart controllers > > that can reduce the drive when they have stopped. And the discrete > > steps they make, which with smart controlers can be subdivided by > > microstepping, look like a prob lem but in the world of flying > > swarf, not terribly important. > > And even burning that power, the torque to hold a 1/16th microstep is > only 10% of the full step holding torque, if I caught all of what was > said in a LinuxCNC youtube clip I looked at last night. (It was in > German, and it's a while since I used mine.)
True, so when I want to really calculate, I use an error that is at least 1/3 rd of a full step as the worst case. But I've not calculated that recently, since I put ball screws in the mills xy table drives. They, being faster will make that a sloppier tolerance. > > But unless the current mapping in the controller is exactly matched > > so that a 1/8th step is exactly 1/8th step, there will be a cyclic > > positioning error. Miniscule, its less than .001" at any point when > > direct coupled to a 5mm per rev ball screw. Best match I would > > guess is when the motor is being run at exactly its nameplate > > amperage. With commonly available stepper drivers having a dip > > switch current setting that typically changes in 10 to 15% > > increments, this isn't as easy to as it should be. > > On a 3D printer, free of cutting forces, I figure microstepping would > be OK at constant velocity, but rubbery under strong acceleration. At > least it's only full steps that you can permanently lose. One of the reasons I, as a general rule, do not set accels to more than 50% of what it tests that it can do. So I can definitely hear it doing its "whee" as it starts up for a G0 move. > > Thanks for reading this far, stay warm guys. We're collecting more > > white stuff this morning. > > There's been an awful lot of it in some states, we hear. Once it's deep > enough, mebbe just tunnel through it to the workshop. (I spent an > afternoon skiddooing at Whistler, years ago, on 7 meters of snow.) > We don't have that stuff here. We just need a way to stop dumb parents > from broiling their infants in cars. (see sig) We have that same level of idiocy here. Unfortunately for the children so trapped. I am in West Virginia, and have nominally 10" on the ground. But I learned to drive in a bad Iowa winter 65 + years ago, so 10" isn't a big problem for me. I might have to put my "West Virginia Cadillac" (a 99 GMC 3 door pickup with 4wd) in 4wd for 6 feet to get out of the drive. We're about out of milk & some onion buns + Dee needs her daily crossword fix from the paper, so I will be out in it in another half hour. > Erik 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> ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
