Re: re:Sanyo "Step-Syn" Stepper Motors

cnc4me writes:

>How do motors run with the modified half step. Did you notice a big
>differance in resonance and torque. Can you compare it to
>microstepping in smoothness.

Not sure if you're asking what is modified 1/2step, or just how does
it do?

Modified 1/2step is not micro-stepping, but it's as close as you can
get to it without actually varying the the phase current(amps)
relationship(s).

What it is, is in one of my previous posts.

So, to answer:

BIG difference between full step RESONANCE and (plain)1/2 step.

BIG difference between plain 1/2 step TORQUE and modified 1/2 step.
The empirical(real world) difference was that the machine(s) could
run more reliably to higher speeds.(for a given motor/machine combo).

I'm a microstep virgin.(please, be gentle) Haven't found the NEED to
use 'em. And until recently, pretty pricey stuff. (thank you Mariss)
I really wish Geckodrives would make a divide by 4 version of his
stepper drive. Probably will try the pulse-averaged version.

Micro-stepping is a good thing, but we don't talk much about its
pitfalls(in perception, not the drive). Slapping a micro-step drive
on one of our machines where a 1/2 step drive was DOESN't really give
us that many more steps(usually). Microstepping was developed for the
extreme low friction electronics mfg. machines where the torque used
to move the slide is minimal, and constant.

What happens in our end of the spectrum is that lots of these micro-
steps get "eaten-up" by the friction-stiction of our ways/slides.

Why? The actual torque change in a micro-step is inversely related to
the number of microsteps per step.

In full step, we have coils 1 and 2 on, 100% power to each. At the
next step, we turn coil 1 off, coil 3 on. This 100% change creates
the holding torque of the motor,AND creates the force to rotate the
motor.(100% in each case)

With micro-step, it's a little different. Lets start at the same
place, 2 coils on, both at 100%, and we'll assume 10 microsteps per
step. Now when we want the first microstep, we take the 2nd coil to
90%, and the 3rd to 10%. We still have 100% HOLDING TORQUE(90+10),
BUT our "rotate the motor" torque is only 10% of holding torque!

So, IF we didn't overcome the friction/physics of our axis/slide we
don't move! At the next step(assuming we didn't move) the force is
20%, and the next, 30%, until we have built up enough torque to
ACTUALLY move. Then the process repeats. And if our machine loads
change and are "seen" by the motor,it WILL be an "uneven" repeating.

Keep this in mind when you're planning your "machine resolution". The
"actual" steps per inch(SPI) may not match the "theoretical" SPI.
BTW, the same thing CAN happen with 1/2 and full step, it's just not
as likely, since the rotational torque changes are greater, and we
usually get "close to right" on the motor size.

Another thing to be careful of if you're counting on those microsteps
is that most drive/motors are not matched so that the microsteps
actually divide the full step evenly! Electrical Amps don't always
match gaussian distribution!(motor magnetic characteristics)

The reason we all like microstep is that there is less "ringing" of
the motor since each step movement is across a smaller distance.
Think of running vs. walking. Strides are bigger, and its harder to
stop on a dime. Which is what we're asking the stepper to do.

Less "ringing" means less resonance, and smoother drives. But do keep
in mind what I've mentioned above.

Hope this helps.

Ballendo