On Friday 16 September 2016 23:46:13 Chris Albertson wrote:

> Gene,
>
> I think I understand now
>
> On Fri, Sep 16, 2016 at 6:07 PM, Gene Heskett <ghesk...@shentel.net> wrote:
> > On Friday 16 September 2016 12:06:47 Chris Albertson wrote:
> >
> >
> > Lead screw is a 1605, 40 tooth gear on the motor by way of a
> > taperloc hub I made, ditto for the 80 tooth gear on the screw, so
> > the motor is running 2x the speed of the screw.  The motor is
> > running on a 39 volt power supply, with a 2M542 driver set for 16x
> > microstepping. Motor is an 8 wire 432 oz/in, wired in series. I am
> > useing a similar if not identical, direct drive on the smaller x
> > screw, wired parallel. It doesn't move very far, maybe 4" total, but
> > its speed for in and out running a g76 threading routine is way more
> > than enough.
>
> So 200 x 16 x 2 steps per revolution is 6400.
> then 6400 x 5 steps per inch is  3200
> at 60 inches per second you are doing  380,000 steps per second
> or, that is 2.6 microseconds per step.
>
> I am very surprised at the low performance of the opt coupler in the
> breakout board
> unless it was intentional.  The signal might be intentionally low pass
> filtered
> in an attempt to reduce noise.   That would be a reasonable design
> for a breakout board.   The designer never assumed anyone would would
> run steps at 300KHz.

Not intentional at all.  The object in these designs is cheap, so they can be 
sold on ebay at a handsome profit for a 10 dollar bill. In fact, the 
elimination of the opto-isolator saves the maker the cost of them even if he is 
buying them at .17 USD a line.  But it makes the difference between a board 
that can handle megahertz pulses without them, and a board that is in trouble 
at 200 kilohertz.  Being dumb, I bought one with the opto's on it, and wound up 
tracing out the circuit and removing the opto from the pin that was driving the 
Pico pwm-servo that was running the spindle motor. It was changing the pwm's 
pulse width so much that the PID module simply could not cope with the 
resultant error.  Taking that opto out of the signal path and I now get within 
5% of the requested speed without resorting to a very complex lincurve setup I 
first used.

So look at the pix carefully, and don't click the buy button if you see a row 
of teeny little 4 pin ic's on that board, those are the opto's.

I can't buy my fav breakout board anymore as cnc4pc has disco's the C1G rev 4 
board. It has an led tally on every pin, making setup troubleshooting a breeze. 
 So I bought a pair of a $10 board that should be pretty transparent to run an 
11x36 Sheldon lathe I am converting.  But, I'll have to drag out and hook up a 
choice of scopes to verify things as I wire it up, something I'm probably a 
month+ away from doing.

There are probably 10 different firmwares that one can install into the 5i25.  
For simpler stepper machines, the prob_rfx2 firmware is probably the best, it 
gives you 2 encoders, two pwm generators, and 8 stepper drivers on the two 
ports the 5i25 has, one db25 and a second one on the 26 pin idc header along 
the top edge of the card.  You can buy a cable assembly that puts the second 
db25 in a spare slot if one can be opened up, or routed out thru a crack in the 
case, I've done both as I keep a box of cable and a bag of crimpon db25's so I 
can make my own of the length and gender I need.

You specify how many of each to use in the loadrt line of your hal file & what 
you don't use is still available as gpio pins.

> To move 60 IPS coins software I think it looks like I might need a
> direct drive
> using 1/2 steps  for 400 steps per revolution.  But I'd be at only
> 2,000 steps per inch

Not enough accuracy, half a thou per step, and at just 2 steps, noisy. 
Smoothing the stepper motion by a /8 or a /16 will make your machine much 
quieter. 99% of the stepper noise from TLM is the backlash in those two gears 
driving the z screw, and they are tightly meshed so the backlash from that 
source might be .00005". Far more in the worn screw because it hasn't a swarf 
cover and swarf has eaten out the felt screw wipers in the nut. I've had to 
raise the backlash comp in the ini file twice now and should replace that 
screw, or at least refill the nut with bigger balls.  That, having done it 3 
times already, can be a tedious job. One of the things I am doing to the 
Sheldon is to seal up the X screw to keep swarf out of that area completely.  
And I have bellows style covers on a boat someplace for the nearly 4.5 foot z 
screw, a 2505 thats 1480 mm's long. I think the pair of long bellows should be 
here next week.

The first half of the fun is building it, the 2nd half is using it. :)
I am momentarily proud of the work TLM is doing, but I'll probably push my luck 
and break something.

With a 1 hp treadmill motor in it, it has a reputation for breaking drive 
parts, but I keep replacing the weakest link with something better, so 
eventually a 10mm XL belt will turn into an anchor chain. :(

[..]

Take care Chris.

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>
------------------------------------------------------------------------------
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users

Reply via email to