On Monday 27 May 2013 14:22:12 Steve Stallings did opine: > <snip> > > > Arturo has finally realized that the so-called reversing > > relay lashup he > > has on the C41 is worthless because it cannot be controlled > > independently, > > instead dropping out a few milliseconds after the PWM stops. > > That will > > destroy motor controllers and may damage the PM field magnets > > when the > > controller suddenly sees a motor it thought was turning 7 > > grand in reverse, > > suddenly being put in the fwd mode with no time to brake it, > > and the analog > > from the PWM has not decayed to zero yet. > > > > I think your 106 also does this as I put a dropout delay in > > the .hal file > > for my mill, and that did not stop the controller from > > thumping the motor > > pretty hard when I issue an M5 to stop the tool from about 250 rpm in > > reverse, which I use, along with a G38.2 command to find the edge of > > something. The slowly turning bit makes a good contact (I > > have a .2 uf cap > > across the probe so it "stores" the momentary contact without > > touching the > > work hard enough to mark it) > > > > So the next run of C41's he makes will do the reverse as long > > as commanded > > from its input. > > > > FWIW, that is not a problem with the 106 when running it from > > the hand > > switches, then it works correctly, but then my dynamic > > braking there is > > resistive. > > <snip> > > I have a somewhat different viewpoint on how the interface > is intended to work. The job of the interface is to supply > control information to the motor driver representing the > desired operation of the CNC program. It is the motor > driver's job to assure that the drive electronics does > what is reasonable for the motor that it runs. Using the > direction command requests from the interface to directly > control relays that switch the high current armature leads > of a DC motor is not workable for a general purpose interface. > > The most common type of control interface for VFDs and > high power DC motor drivers is one that accepts one switch > that closes when forward run is desired and one switch that > closes when reverse run is desired. This interface must > open both switches to indicate stopping the motor. The > alternative Run and Direction (European style) interface > could accommodate holding the direction signal while stopping > the motor, but that still ignores the issue of how long the > control interface must be stopped before it is safe to > request running in the opposite direction. > > VFDs and DC motor drivers with internal reversing circuits > take care of the requirements to safely reverse the motor > in response to their command inputs without expecting the > command generator to follow any special rules. > > A special interface that accommodates reversing DC motors > by controlling a relay that reverses the armature leads > could be done, but it is not trivial due to the stored > energy and the need to brake the motor. The market share > of DC motor drives relative to those powered by VFD driven > induction motors is small and we have not addressed it > directly. > > Steve Stallings
Perfectly valid viewpoint as there are probably 10 machines using the 106 for vfd control for every hobbiest like me doing it on the cheep. However, for one off's like me, I don't have a problem putting a flip flop into the hal file, along with a time delay and probably an AND or two, with the delay set for however long it takes it to stop from wide open. Use the delay to lock out any dir change signals until its safely stopped. IOW, software is a cheap solution provided the hardware can be addressed closely enough. Using separate fwd and rev relays still suffers, or does it, since in that case, both relays would be open and the braking R's connected by the backside contacts. Lemme study up on how to wire the DPDT contacts though, that truth table escapes me ATM. Is there a sample diagram in the wiki for that? Maybe I could use the C41 in the US mode? Its been so long since I built the control box for the mill that I don't recall how I have the 106 programmed, but I'm using the fwd signal & relay to energize an ice cube, connecting the motor to the second, reversing ice cube. When the fwd relay goes off, a 20 ohm 20 watt catches the back emf of the motor, stopping it in about 2 seconds. But on the lathe, with this motor, the moving mass is 30x the mills moving mass, so a coast down from the new wide open is about 13 seconds. The new wide open is 1200 with the back gear in high & thats probably more than fast enough for me. To get the 'new' above I grabbed another piece of pcb stuff and soldered an LM317T to the middle of it, then super-glued it to the top of the power transformer so its about an inch away from the original, then trimmed a fixed R2 at 2.666k and its putting out 15.50 volts, so the C41, with a 98% pulse in, is now making 13.5 volts into the motor controller, gaining me another 25% in both gears. Looking at PID.0.error, and calling for s1200, it isn't limited, the error is floating in the general area of zero. And that motor is genuinely singing a high baritone, with its cooling fan sounding like an unintentional siren. Got the rider accessible part of the yard done, but now it can't make up its mind it its going to rain or not, I got dribbled on a couple times while making up that LM7815.5. And I refuse to weed eat wet vegetation. Besides, I should cut a rose or 3 and take them out to Dee's mothers stone. 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> There are certain things men must do to remain men. -- Kirk, "The Ultimate Computer", stardate 4929.4 A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ Try New Relic Now & We'll Send You this Cool Shirt New Relic is the only SaaS-based application performance monitoring service that delivers powerful full stack analytics. Optimize and monitor your browser, app, & servers with just a few lines of code. Try New Relic and get this awesome Nerd Life shirt! http://p.sf.net/sfu/newrelic_d2d_may _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
