Re: Going home / more stepper speed!

Jon, Mariss, Ballendo and the list,

I did some experimenting last night, got a current probe (2ma/mv
Tektronix) and looked at a motor winding's current. I can see the
triangular current waveform of the +- 2A current responds to the step
pulses. At quite slow speeds, A pair is seen (full step). Half step
shows one current pulse with a lower amplitude. faster speeds, and the
previously separate pulses merge together, forming a continuous change
from one pulse to the next. Sometimes the "sides" of the pulses are
nice and "flowing" (a little wavy), other times the motor gets a little
noisy, and I see "jags" on the sides of the pulses. No "ringing"
observed. Probably not looking the right way yet. I did notice that at
high speeds, the peeks don't make it out to +- 2v. I've got 37v from
the raw DC of a 24v 4.8a linear supply. This is with a NEMA #34 150
oz/in 2.54V 3.1A motor. an API CMD-50 stepper module drives it (100k
programming resistor). Poor match, I know! Not enough drive! I'd like
to try one of Dan's or Mariss' drives on it.

I've got one of Dan's tach's coming from Larry, and I'm able to count
the pulse rate/duty cycle pretty good with the hand held computer.

I connected up TRW/Globe dc motor to the spindle of the Sherline, and
spun it up. at full speed (old Sherline spindle), I got about 17v, with
.13v ripple. The ripple was smooth, and looked like three "traces"
interwoven together. The other little motor (disk drive) had a AC tach
on it's end. The BIG pittman was too big for the spindle test. The
small pittman had a gear box on it (not tested!). So a little motor
would work for a tach.

And I got a good lesson on how Windoz98 makes a mess of software
generated stepper pulses! Made a mess out of 'em. Couldn't get rid of
it. I had to resort to a DOS622 boot disk! But I did get 22+ Khz.

Also took a look at Henrik's stepper board layout on Eagle's newest
"freebie" board layout program. I still don't know how to run the
program. It is supposed to be able to Gcode (had Gerber before)!

Alan KM6VV


Jon Elson wrote:

>
> Alan Marconett KM6VV wrote:
>
> > Hi Jon,
> >
> > I also have a small pittman motor w/tach end. I think it was for a
> > floppy disk drive. Any better? The pittman I was originally thinking
> > about is fairly big, 1/4" shaft, 1.5" dia, 5" long, approximately. No
> > idea of specs.
>
> Well, if it is used for a sensitive speed control application, it would be
> a better class of motor than for spinning a fan, for instance. The tachs
> on most of the floppy drive motors were AC. Anyway, the best way of
> finding out is to spin it with something that runs at a constant speed
> (drill press or mill spindle comes to mind) and see if you get waves
> or a straight line.
>
> > And I'll try a current probe on a motor winding...
>
> It will take some analysis to figure out what you are seeing, but if you have
> it stepping at 50 - 100 steps/sec, you should see little wiggles after the
> steps.
>
> Jon