I wondered if that might be a problem. I'm thinking I could use a manual pulse generator to square it up at startup and have a set of home switches that could be touched off on as necessary to assure that the system is still square. If it isn't then the operation would be stopped and it could be manually squared again.
It is my understanding that the usual cause of missed steps is heavy loading of the motor. Assuming this is minimized, I think this might be a viable system. Keep in mind that this a hobby setup, so other things besides pure economics drive the decisions. Raymond Julian Kettle River, MN The things we admire in men, kindness and generosity, openness, honesty, understanding and feeling are the concomitants of failure in our system. And those traits we detest, sharpness, greed, acquisitiveness, meanness, egotism and self-interest are the traits of success. And while men admire the quality of the first they love the produce of the second. -John Steinbeck, novelist, Nobel laureate (1902-1968) On 06/12/2014 04:53 PM, Gene Heskett wrote: > On Thursday 12 June 2014 17:09:45 rayj did opine > And Gene did reply: >> A general question on using two motors in this situation. I'm using >> steppers, so I'll frame the question for them. >> >> Assuming identical motors and driver boards, is it possible to wire >> both driver boards to the same output from the breakout board. >> Example: run the wires from the BOB X-axis step pin to the step input >> for 2 drivers and the X-axis direction pin to dir input on both >> drivers? Power, watch dog, etc. wired as necessary for safe >> operation. > > Generally speaking, Not before a good, gantry is square, home has been > achieved. > > Why? Because there are going to be residual mechanical sync errors > between the two motors that will push one or both to be slightly out of > sync with the other when powered down, that, coupled with the fact that > most stepper drivers power up at what they think is the home/index > position, and the motors will turn to the nearest position from where they > are, making it possible that they are a major portion of a full step out > of sync just from being powered up. How far out of square the gantry is > depends on your gear ratio's of course. > > The ideal situation would seem to be a switch on each end of the gantry, > that when it is just closed, would stop the driver on that side while > allowing the other side to continue looking for its switch. And I would > like to see a counter that would stop it and advise the operator there is > a potential square error if it counts to 1 or 2 more than the driver is > microstepping. Something in the drive on one end or the other may have > slipped. Such a warning might save you from making 20 parts, all of which > are out of square. >> > Once this synced state has been achieved, then it might be feasable to > drop to one stepgen. But since you had to have two to home properly, you > may as well go ahead and use both. > >> 2nd question: Is there a glossary/dictionary of terms/acronyms used >> regularly on this list. I have a hard time figuring some of them out. >> I'm thinking of LCNC/machining terms, specifically. >> >> TIA > > ISTR there is a glossary in the various pdf manuals, last couple of pages > are where I'd check. > > I hope this is helpful Raymond, but someone else here may have a better > idea. I'd almost bet on it. ;-) > >> Raymond Julian >> Kettle River, MN >> >> The things we admire in men, kindness and generosity, openness, >> honesty, understanding and feeling are the concomitants of failure in >> our system. And those traits we detest, sharpness, greed, >> acquisitiveness, meanness, egotism and self-interest are the traits of >> success. And while men admire the quality of the first they love the >> produce of the second. -John Steinbeck, novelist, Nobel laureate >> (1902-1968) >> >> On 06/12/2014 03:42 PM, Viesturs Lؤپcis wrote: >>> 2014-06-12 16:52 GMT+03:00 Todd Zuercher >>> >>> <zuerc...@embarqmail.com>: >>>> I don't really have a good reason, more exploring options and >>>> thinking out loud, not really wanting to fight with the problems >>>> with gantries in LinuxCNC, >>> >>> Well, I do not see much issues with LinuxCNC regarding gantry >>> machines. So far (up to 2.5.4) there have been 2 things to watch out >>> for: 1) machine would remain in joint mode, if MDI command is >>> executed through halui from pyvcp button (this affects any machine >>> with nontrivial kinematics);. >>> 2) operator has to remember to switch to world mode after homing all >>> joints, otherwise jogging machine will cause jogging just one side of >>> gantry.. >>> >>> First one is fixed in 2.6 branch. >>> Second one is fixed by something like 30 minute (including dowloading >>> source code from git) setup routine - start by adding few lines to >>> Axis script to create hal pin in Axis GUI that switches to world >>> mode, then connect it to axis.n.homed pins through and4 module >>> (created by customizing and2 module). >>> >>> I do not know of any other gantry-related issues (just spent another >>> 5 hours with my gantry router and making some chips, LinuxCNC works >>> just wonderfully). >>> >>> Viesturs >>> >>> --------------------------------------------------------------------- >>> --------- HPCC Systems Open Source Big Data Platform from LexisNexis >>> Risk Solutions Find What Matters Most in Your Big Data with HPCC >>> Systems >>> Open Source. Fast. Scalable. Simple. Ideal for Dirty Data. >>> Leverages Graph Analysis for Fast Processing & Easy Data Exploration >>> http://p.sf.net/sfu/hpccsystems >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> ----------------------------------------------------------------------- >> ------- HPCC Systems Open Source Big Data Platform from LexisNexis Risk >> Solutions Find What Matters Most in Your Big Data with HPCC Systems >> Open Source. Fast. Scalable. Simple. Ideal for Dirty Data. >> Leverages Graph Analysis for Fast Processing & Easy Data Exploration >> http://p.sf.net/sfu/hpccsystems >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > Cheers, Gene Heskett > ------------------------------------------------------------------------------ HPCC Systems Open Source Big Data Platform from LexisNexis Risk Solutions Find What Matters Most in Your Big Data with HPCC Systems Open Source. Fast. Scalable. Simple. Ideal for Dirty Data. Leverages Graph Analysis for Fast Processing & Easy Data Exploration http://p.sf.net/sfu/hpccsystems _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
