> I would assume the motor(s) in question are being > microstepped? Yup, quarter-stepping. It's a modified Sherline controller with custom firmware that I described in my Circuit Cellar magazine column a few years back.
Given my ferror blunder, I decided to figure things out from first principles. The complete INI and HAL files are at: http://pastebin.ca/266891 http://pastebin.ca/266894 Here's my reasoning; but check to see if these values make any sense... The controller can run a bit over 8000 quarter-step/sec = 2000 full step/sec = 10 rev/sec = 0.5 in/sec = 30 in/min. That's aggressive for a Sherline, although I long ago captured the end of that Y axis leadscrew in a bushing block to keep it from whipping around. The max step rate means a 125 us period. I set base_period = 25000, giving 5 ticks per step. The controller firmware triggers motor steps on the falling edge of the Step signal, so the timing parameters in the HAL file are: steplen = 2 stepspace = 3 dirsetup = 1 dirhold = 3 I applied a 'scope to the pins of the PIC microcontroller and found the RC filters knock the rise and fall times to about 20 us. That means a 50-us Step pulse rises to full amplitude with no problem. Back in the INI file, the settings are: default_velocity = 0.0167 (slow enough) max_velocity = 0.50 (30 in/sec, at best) default_acceleration = 2 (limited by axes) max_acceleration = 4 (ditto) All three linear axes are identical: max_velocity = 0.50 (optimistically) max_acceleration = 0.5 (see below) stepgen_maxvel = 0.60 (about 10% up) stepgen_maxaccel = 0.6 (ditto) ferror = 0.015 (seems OK) min_ferror = 0.002 (ditto) In the middle of long jogs the thing actually ticks along at about 320 us/step = 3000 step/sec. So it seems EMC2 limits the velocity to 11 in/sec. I don't know why that should be true, as lots of you folks are running -way- faster than that. The max_acceleration value is experimental. Below 0.4 the motors wind up veeery slooowly, above 0.5 it produces following errors. That seems to be an unduly small range, but the raw step pulse parameters shouldn't be the limiting factor. I based the ferror values on the "under half a turn" principle, then cranked it down until I got following errors. I think these settings are sub-optimal, as G1 moves at 20 in/sec (actually much less) around a 0.5-in square produces really nice fillets on the corners: perhaps 1/8" radius. Obviously, slowing down reduces the fillets, so it's an acceleration thing. The motors are audibly winding down for the corners, so I -think- they should be able to withstand far higher acceleration, but higher max_acceleration goes into following-error territory. Perhaps this is caused by the internal PID loop tuning for the steppers? Or maybe it's just another round from my footgun? Anyhow, these settings have completely (uh, so far) eliminated the "half turn the wrong way" and "completely wrong direction" behavior, but I can still hear the motors taking an occasional hit from the bogus Direction signals at the start of some motions. I connected a counter to the Step signal and found that it always squirts out the correct number of Step pulses for either move, so the Direction signal really is backwards for a bit. When a motor takes a hit, it moves a few mils short of the command, anywhere from a fraction to maybe 0.007 in). With quarter-stepping, 0.001 in = 16 steps, so the motors really do get confused by those Direction glitches. These events are fairly rare and I did not have time to capture screen shots that provide more information that we already know. It's entirely possible the hypersensitivity could be due to an error in my controller firmware, but this seems to be new behavior with EMC2 and may be explained by the (known) Direction glitch and (supposed) motor mechanics. I'm off on an unexpected journey, but should be back by this weekend. I'll try scoping the PIC microcontroller's I/O to nail down exactly what's going on when the motor takes those hits. -- Ed ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
