On Wednesday 02 October 2019 23:41:38 Brent Loschen wrote:

> On 10/2/2019 7:18 AM, Gene Heskett wrote:
> > On Wednesday 02 October 2019 00:36:41 Brent Loschen wrote:
> >> <https://www.ebay.com/itm/Mini-Peristaltic-Pump-Head-With-Tube-Smal
> >>l-F
> >> low-Stepper-Motor-OEM-Package/273419600046?hash=item3fa91400ae:g:h1
> >>MAAO SwMdZbe77a>
> >
> > I sorta went crazy, ordered two kits of telescoping brass tubing to
> > help make better, smaller nozzles. I can solder up a 1/16 od, and
> > redrill it at #80 to get an even smaller tip. Then off this link,
> > which takes a short nema 42 motor with a 10mm shaft (no way do I
> > have a motor that big), but I did find a 12 volt rated peristaltic
> > that looked usable at $6.32/copy. So since even the silicon tubeing
> > has a limited lifespan in service of only a year or so, I bought 4
> > of those. But they're in china, so a Nov 1 estimated delivery date.
> > Spit.
>
> If you check out the mechanical drawing of the pump in the link above
> (last thumbnail to the right), it appears to have both 31mm and 47mm
> c-c mounting holes which match  NEMA 17 and 23 steppers respectively. 

The only mech specs are  at the bottom of the page, and say a nema 42 
with a 10mm shaft to drive it.  But thats usually a smaller nema 34, the 
two 34's I have have 15mm shafts, but are 960 and 1600 oz-in motors, and 
still way too big physically, adding considerable weight to the gantry 
if mounted there.  I think I can pwm over at least a 10/1 ratio using 
the ones I've bought. SW is cheap, even a nema 23 is 35+ bucks, and 
weighs 10x what these do.  I may be wrong, have been before, but you'll 
see it here when I am.

> Not sure why they reference a 42 motor which has a larger bolt pattern
> (89) than the overall dimensions of the pump (57)!
> Although it would be nice to have adjustable spring tension on the
> pinch arm to accommodate a wide range of pump tubing, it's hard to
> beat the price ($13 delivered) for a 6 roller pump.  Precise speed
> control of a stepper should be a lot simpler than to PWM a DC motor. 
> Would it be possible to treat that pump/stepper as a joint and set the
> RPM via feedrate in Gcode? 

Yes and no. We can name the signal anything that doesn't clash with LCNC, 
and set its speed in gcode, but I suspect it would involve some pyvcp to 
set the speed if we want to vary it from the gui. By useing one of the 
motion.analog i/o's to get it into hal.  Set up an on cycle just long 
enough to move the pump 2 or 3 degrees, and leave it off for a pyvcp 
interval. With a hard enough bang, the on time needn't be more that 2ms 
I'd think. 10 such pulses a second ought to be smoothed somewhat by the 
hose to the mister, giving a reasonably continuous mist at the nozzle.
I have some power fets to do the switching with as that cycle speed would 
destroy a relay in short order.  Need more wet, bang it 100 times a 
second.  Using a stepper driver in a mesa card, ought to simplify it 
somewhat. I can imagine 2 or 3 ways to skin this cat using these itty 
bitty pumps.

The biggest problem is over coming the drag to get it moving. But I've 
got 12 volts at 5 amps to play with. I'm useing some, maybe 1.5 amps now 
with the air valve and 3 other relays, should be enough left to move the 
motor. hal code is not a problem, I just have to write it, but banging 
the motor hard enough for 2 or 3 mili-secs is.  These particular pumps 
have silicon hoses, so ought to last a couple years, maybe more at a 5 
seconds per full rotation speed.  And that might actually be fast for 
this. From the bubble speed I'm seeing creeping thru the hose with the 
current lashup, I'd guess a rev in 20 secs.

Thanks for the feedback.  But what I'd like to see in a short nema 23 
driving a pump about this size.  That I could probably use.
> Brent
>
> > Now if I can write hal code to allow enabling a PWM module to drive
> > this for speed control, at the same time the m7 is on, and some more
> > pyvcp to dial the speed via controlling the pulse width, I should be
> > set better than I am right now. Enough air pressure to keep the work
> > area clear, and just enough fluid to cool things without soaking the
> > neighborhood.
> >
> > The stepper drive is a nice idea, and I may yet pull one of the
> > 225's off the remains of the hf and put it on this 6040's z drive. 
> > OTOH, unless I start doing a lot of 3d woodworking, this is fast
> > enough. Famous last words...
> > ==========
> > Speaking of PWM, is it possible we (meaning LCNC) have a means to
> > detect the rise in back emf as the motor starts to turn, effectively
> > pulsing the motor so it has enough power to overcome roller
> > friction, but would them turn it off after 2-10 degrees of rotation?
> >  Should make a much more controllable low flow speed control.
> >
> > Somehow, I doubt we could turn it off and sample the back EMF with
> > one of a 7i76's 12 bit A/D's fast enough to make that work, and the
> > docs don't say how long to a valid reading, but can you tell me,
> > Andy or Peter?
> >
> > That way I could use a solid 12 volts to bang it with, detect that
> > the motor is moving, extending the pwm's off time for speed/flow
> > control and that should allow flows that hardly wet a finger.  Or
> > have I let my imagination out to play w/o a chaperone again?
> >
> > Won't be the first time, and I hope not the last. :)
> >
> > Thanks.
> >
> > Cheers, Gene Heskett
>
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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)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>


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