Re: [Emc-users] Drive Tuning

[gene h. <ghe...@wd...>]

On Saturday, April 28, 2012 02:10:14 PM Joachim Franek did opine:

> see chapter 4ff Rigsby_James.pdf:
> http://uwspace.uwaterloo.ca/handle/10012/5325
> 
> Joachim
 
Wow!  That is quite a dissertation.  Contains way more math than this tiny 
brain ever had to learn since electronics is fairly simple despite being 
largely invisible until somebody turns on the light. :)

I liked the 2 conclusions arrived at, first being that X speed is the 
limiting factor, while ATM, x is the weakest motor on my toy as its an 
escapee from the H&R catalog, a 52 oz/in 4 wire that I am running at about 
an even amp ATM.  Direct coupled to the back end of a 10mm metric screw 
which is a nominal 20 tpi, it is currently being hit with accels of around 
9 in the ini file, and seems quite capable of 30 ipm despite a lack of a 
back shaft and damper.  The hand crank is still on the front and I'd guess 
it peaks at 1000 rpms.  Just a blur.

From his comments on under load frictional torque, I now think it will skip 
steps or freeze if asked to move with cutting forces applied when making 
metallic swarf.  However, it is quick!  I can sub an 8 wire 425oz/in in 
that position, running it in parallel 4 wire mode by cranking up the 
current, one of them is presently running z, wired in series with about 
2.35 amps and can do 32 ipm w/o a damper.  The controller can do 4.2amps so 
that seems doable if 350oz/in is enough, but can that 425, a triple stack 
nema 23 turn that fast?  TBD. The downside is that it will add at least 
another pound of weight/mass located with its CG about 6" to the rear of 
the carriage, making the front gib tension a lot more critical to keep it 
from tipping back and up off the only V way it has when no downward cutting 
forces are present.

The other conclusion is that without a true bipolar drive to the spindle 
motor, treating it as a C drive servo, and a complete gear it down redesign 
for lower speeds, I'll never be able to do something like those table legs 
even in miniature (for a music box or clock...) on this 7x12.  Reality 
strikes in force. :(

Question:

NURBS, now that I've read an explanation of what it is when you folks throw 
around a strange acronym, does however look like it promises both speed 
increases and higher tracking accuracy.  So how do I bring that into play 
in the trajectory planner, bearing in mind I'm on the 2.6.0-alpha channel 
with this machine?

I also plan on removing the compound slide and making or buying a tool post 
of the correct height mounted directly on the cross slide, to get rid of 
all the flexure under load the present setup has.  I have a QC setup now, 
but that thing seems to be made out of wet spaghetti painted black as its 
all alu.  Because the much older 'lantern' style tool holder doesn't have 
the offcenter, hanging way off the edge of the slider, forces all these QC 
things impart, that seems to make a lot more sense to me.  But then I'll 
have to make several if I also want to do any drilling.  I've done that 
before, and can show a boring bar 5/8" in diameter and 10" long mounted on 
that puppy already, which is how I made the motor mount for my rotary 
table. ;)  Its also how I ripped the threads out of the top of the compound 
and had to replace it after doing that job.  I needed a bag of shot to 
drape over the far end of it too. :(

A final question:

I am going to make the caster wheel variation of the resonance damper, and 
it appears there are quite a few thoughts on achieving the correct coupling 
'looseness' for best effect.  Some are using frictional losses, allowing it 
to actually turn on the shaft, some are viscous but ultimately rigidly 
pinned allowing it to be used as a handle to turn things, and some I've 
read about have cross drilled holes in the rim with big lead buckshot, one 
per hole, which I assume are intended to have some 'rattle room' for the 
shot as opposed to just using it as rim mass.

So, does anyone have any pix or drawings of one that you know to work well 
on Nema 23 motors?

I tried one of mine, the stacked fender washers & rubber dampers on my z 
yesterday, but its steel core to hold all the fender washers & rubber added 
enough rotary mass I had to cut the accels in half on my Z to stop the 
stalling, which wasn't exactly what I expected.  So the rim heavy caster 
wheel seems like the lessor of a rotary mass evil to me.

Comments?

Thanks & Cheers, Gene
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