Yes, I had a stepper system run backwards when pushed too hard. I believe it was a combination of accel and start frequency being too aggressive. However, the backwards motion was NOT smooth or at commanded speed- slow and noisy is what I remember. Jeffrey did not report, though, that his backwards motion was anything but normal except direction-wise. So, I'm thinking this isn't the case here.
Glenn -----Original Message----- From: emc-users-boun...@lists.sourceforge.net [mailto:emc-users-boun...@lists.sourceforge.net] On Behalf Of Gene Heskett Sent: Tuesday, July 07, 2009 7:30 AM To: Enhanced Machine Controller (EMC) Subject: Re: [Emc-users] Weird EMC2 tuning issue (direction reverses intermittently) On Tuesday 07 July 2009, Andy Pugh wrote: >2009/7/5 Jeffrey Pease <jpe...@peasej.com>: >> One mysterious issue I've seen that I'm trying to figure out is that >> very, very rarely, a movement command to the milling machine will >> make an axis move the correct distance in the INCORRECT direction. > >Is there any possibility that this is a mechanical problem with the >motors? I am wondering if they can get into some form or resonance when >pushing the step rate too far, such that they start stepping backwards? >Note that I don't even know if this is possible/ Yes it is, particularly when using a driver that can't microstep. Resonance can build up to the point where its actually turning backwards due to the magnetic spring action, and it could find it easier to keep on turning backwards, having overshot the center. I have not personally observed that in my machine however, cuz if it skips a step, mine just locks in place and sings. Dampers will help to squash this, allowing considerably higher speeds. The dampers should take the form of loosely coupled weights that can slip and therefore absorb the resonance motions. Mine are built from a steel spool with one flange removable and adjustable, with alternating layers of sheet rubber whose center holes are a drag fit on the spool hub, and large fender washers that are free to turn on the spool hub. The removable flange is adjusted so that the stack of washers/rubber is snug but can be turned in place when the motors are powered up & locked. This works well for microstepping drivers such as the xylotex I use, allowing about 2x speed increases but probably needs a more mathematically based design for stuff running at half or full step. They can be see at <http://gene.homelinux.net:85/gene/emc> -- 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) The NRA is offering FREE Associate memberships to anyone who wants them. <https://www.nrahq.org/nrabonus/accept-membership.asp> Celebrate Hannibal Day this year. Take an elephant to lunch. ---------------------------------------------------------------------------- -- Enter the BlackBerry Developer Challenge This is your chance to win up to $100,000 in prizes! For a limited time, vendors submitting new applications to BlackBerry App World(TM) will have the opportunity to enter the BlackBerry Developer Challenge. See full prize details at: http://p.sf.net/sfu/blackberry _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Enter the BlackBerry Developer Challenge This is your chance to win up to $100,000 in prizes! For a limited time, vendors submitting new applications to BlackBerry App World(TM) will have the opportunity to enter the BlackBerry Developer Challenge. See full prize details at: http://p.sf.net/sfu/blackberry _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
