Inches Per Second - spinning a stepper is fun, but rapid'ing the CNC world's "mine's bigger than yours" comparison.

 

IPS. Wouldn't that be based on the diameter of the gear at the end of the stepper shaft?
Or is IPS based on a standard gear size?

I have not tested this IPS, but from math.....does the following make sense?
(Driver at 1/8 step. Motor 200s/r or 1.8deg. Gear Perimeter 2.25")
So each full turn of the shaft, the motor travels 2.25".

With a STEP signal of 60Khz...
60Khz/(200 steps/rev) = 300 Turns in 1 sec...

So if my stepper is turning 300 times in 1 sec....
And my travel distance in 1 rev is 2.25"
Thats 675"... Somethings wrong?
That's 56'


I'll have to try it out?

Again with the IPS.
Is that based on a standard step signal, or gear size?

I just feel there are too many variables to compare IPS.

 

It's assumed that the stepper(or servo) motors are already installed in the CNC setup, and the measurement is relative to the machining head. At some point steppers will start to torque-out(i.e. miss steps) and it can't be used above that point. It's not supposed to be a serious question...

 

inches per second, cm per second.

 

Oh OK.
Hey I'm newbie....just learning the ropes.
The gantry that is driven by these steppers is not allowed to run past 5"/sec. That is a spec'd concern from my customer.
I know it's going 5"/sec.

(Looks slow to me)

End user is happy & he likes the smoothness.

Thats all that counts I guess.

Thanks guys

 

no, you aren't getting 675 ips. you probably forgot the threads per inch of the lead screw. Lets says its 12 tpi, then you would be seeing 60ish IPS which is pretty good. I suspect loading or resonance will kick in somewhere.

 

I have driver in similar configuration... with 8 diodes
http://www.2a.pl/~mark/cnc/a3977/ster3977-22-d.png

I'm using byv27....
but with 31dq10 is better... or 1n5822


my driver is work... with 3A... constantly with 2,8A (and BIG radiator)
but when motor in motion some faulty steps will accur ...
with smaller current too

probably... its problem with noise

my project description:
http://www.pminmo.com/phpBB/viewtopic.php?t=64
http://www.cnc.info.pl/viewtopic.php?t=1783

 

Thats good stuff you have there.

You should try seperating the grounds at the Allegro.
Let the Allegro join the grounds internally.
Made a small difference for me.

 

I make it... for me too

---
now I will tray strait connection form STEP -> to A3977

 

A little update.
With a little help from the folks at Allegro, I found the best thing to do was adjusting the RC components while scoping current on one of the motor windings.
The default components for the RC fromAlllegro is 30K & 0.001uF.

By messing around I found that having a 10K & 0.01uF gave me the best run for my money. REF is set at 2.2V & PFD at 3.1V.
According to Allegro, the 10K & 0.01uF I have chosen are in range for RC values, but since my motor is a little big (10mH), it has all worked out.

Scoping. I was scoping motor windings with locked rotor.
Zoomed right in on flat portion of the STEP, and adjusted the PFD for expected sawtooth waveform.

Motors are back to being a little noisey. And thats because the end user had asked me to cranked up the torque. And as the formalua goes, I get 2.2V for the REF. As I turn down the ref, and thus lowering torque/holding power, the noise slowly dissapears.
My end user will have to determine what sort of torque he wants....and put up with the noise.

I believe we may solve this audible noise problem by giving away a free radio with every purchase!

 

Remember, the noise isn't a bug... It's a feature!

 

???

Rt=10k & Ct=0.01uF=10nF => Tblank = 14us & Toff=100us

in datasheet

0.7us < Tblank < 1.2us
30us < Toff < 46us

 

MarkComp77,
I've taken a screen shot of my engineering report for the project binder.
Here you will see I have scoped a motor winding.
Rotor locked.1/8" step.
Your looking at a step.

Motor is 10mH..

Attached Images

ss.JPG (56.8 KB, 28 views)

 

It IS! There've been a couple of times where the existance/absense of that barely audible, high-pitched hum has made me stop, think for a second, and take a second glance at the cutoff switch - just in time to prevent me from doing something stupid...

 

on yours "Attached"...

??10A??
is It current of A3977 ?

---
PFD=3.1V

in datasheed =>
mixed decay
0.21Vdd > PFD > 0.6Vdd
and if Vdd=5V =>

1.05V > PFD > 6V
i use 2V...

but if you select PFD=3.1 => slow-decay



--
small question:

stepper with BIG inductance (10mH)
need bigger Tblank => bigger Ct ?

i use stepper with 3.6mH....
http://www.2a.pl/~mark/cnc/4a2.jpg