On Tuesday 26 August 2014 06:43:28 Erik Christiansen did opine And Gene did reply: > On 26.08.14 05:13, Gene Heskett wrote: > > I have a box in the basement with 4 ea small steppers designed to run > > from a 24 volt supply, and a bunch of comparators to convert the > > induced voltages into an A/B signal, was going to use them as jog > > wheels, but the one time I tried to setup a test to see if the idea > > had merit, I found that by the time I had added enough hysteresis to > > the comparators, the minimum speed at which a reliable signal could > > be obtained was faster than I had envisioned for fine control. > > Doable, yes, practical for the job, no. > > Adding a bit of DC excitation appears to be the secret. About a > fortnight ago I stumbled across a hardcopy I'd made from out there on > the web somewhere, showing a 680 ohm resistor from each coil end to +5v > or ground, and a LM339 comparator picking off the coil emf, IIRC. > Unexcited, the generated emf was dismal (as you've confirmed), but > leapt to hundreds of millivolts (i.e. heaps) with the coils lightly > energized. Cogging (detent action) increases a bit, giving improved > jog wheel action, according to the author. > With the 24 volt rated motor, I was getting volts per felt cog. But it was ringing like a bell at the comparators output. It may not have effected the usual flip flop based direction detector as it was only one or the other line.
ISTR seeing that link, someplace in time back up the log, and thought at the time that whoever drew the drawing was perhaps not as well versed in electronics as I have been after about 65 years of this. I don't recall that I bookmarked the page, so if you can supply that URL, I'd be glad to look at it and comment again. IIRC: The effect of the 680 ohm resistor was more than likely just getting the comparator inputs off the supply rails far enough to good performance, the LM339 I was using needed its inputs pulled away from the rails a few hundred millivolts unless it was powered bipolar. One generally would do that, and I did, by putting in a bias network to split the supply voltage in the center, and a resistor from that divider then was connected to one end of each motor coil just to supply the bias to do that. By choosing which side of the comparator gets the bias r connected, then the other side gets a much larger r connected as feedback, the really low level noises are suppressed below the trigger point. This occurs due to the windings r causing a few microvolts of diffs between the inputs when at rest effectively locking the comparator output to the last state. It will of course oscillate if you get that wrong. I was at the time, trying to use some of the shacks single sided perf board for a breadboard, but that stuff is so cheap it may fall apart the first time a 275C iron tip hits it. This sort of thing should be worked out using that white plugin breadboard, then made into something useful in eagle, but I never did buy me one of those plugin solderless boards. I always considered them to be a bit pricy... > Due to a lacking round tuit, I haven't yet gone as far as you Gene, > to make one up for storing in a drawer for later. Yeah, I seem to have miss-laid my round tuit too as the years go by. In fact I haven't seen it since we moved from Rapid City in '71. I've been threatening to make some more out of much sturdier alu as that one was a hot stamped maple coin about the size of a silver dollar. I miss it too. But in all this time I have not come across any artwork I could run thru potrace to use to make it, and my artistic ability usually got me a D in grade school. > (Came back a couple > of hours ago, from a fortnight on the farm. The fences are whole again, > with no more trees through 'em, and I have another load of firewood to > get me through what's left of winter. Three local council workers > turned up on one say, to clean up the heavily wooded lane which runs > along one boundary, and dropped another tree through the fence. Still, > I can't complain that we pay our rates, and I never see them way out > there.) These guys can't lay a tree where it doesn't hurt anything? Sounds like a good teaching moment to me. I've made more than 1 6-pack of suds betting on where the tree was going to fall. I don't make those bets in a high wind of course. ;-) Making up a heat sink yesterday to put on one of Jon's pwm driven servo amps I am going to use for the spindle driver on my 7x12, I found I cannot locally buy a 4-40 screw in any length, so I think I'll re-seat it on the mill table and drop a 2 flute 1/4" mill into it to get it down to where the 1/2"ers I have will do. This mornings project I guess since I'm cooling my jets till the mailman drops a box with the amp hidden in it on the patio chair beside the front door. I went online & bought some 1.25" socket head versions, but those are in MN & won't materialize till next week. I hate waiting for pissy-assed little things like 4 screws I can't buy locally... Then, talking about round tuit's, I just heard some very uncharacteristic exclamations from the better half, emanating from the general vicinity of the kitchen sink, she had pulled open the lower door to extract a spray bottle from a small tub sitting under the garbage disposal, and found the tub 1/2 full of dirty water. Seems the disposal's shaft seal in the bottom of its grinder has gone away. Disposal sounds normal. So, saddle up and go get a new one is the days project. Damn! OTOH, thats the 3rd one I've put in in the nearly 25 years I've been here. And even with a 5 year warranty, if I could find it, it has to be 2-3 years out of warranty. The advantages of ones "Golden Years", but the only gold is in the porcelain bowl in the middle of the house. :) Thanks 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> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
