Re: [CAD_CAM_EDM_DRO] Re: Question about steppers

Subject: [CAD_CAM_EDM_DRO] Re: Question about steppers

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Will" <nmbmxer@y...> wrote:
>
> I want to use a stepper to control the quardalift on my shoptask
for
> the z-axis. I know that 960 oz-in will comfortably turn the
> leadscrew, I am planning on reducing it between two and three to
one.
> That puts my torque requirement between 320-480 oz-in.

I will believe you on the torque you require if you are just talking
about raising and lowering the head, and not doing any cutting in the
process.

> The leadscrew
> is 10tpi. My question is this, if I use a stepper that is 1.8
> deg/step, .9 deg/ halfstep, can micro step it to 800 or 1600
> steps/rev?

NO. Micro stepping is used to eliminate motor resonance. The micro
steps them self's cannot be considered true positions. You can only
depend on a full or half step for position when using micro steps.

With a 10TPI screw that would be .1" lead. So .1" / 200 full steps
= .0005" per full step. Half step would be + of that or .00025 per
step.

With that said if you are trying to use the Z screw to move the head
and cut material you have other problems to deal with than
theoretical resolution. For 1 thing the accuracy of the screw is
probably .003" or so a foot. And you have backlash in your lead
screw nuts, maybe .03" to .06"

> I am trying to compare the torque needed to lift the millhead with
> the Speed/Torque curve to see how fast I can make the millhead
move,
> at least in theory. I am having trouble reading the chart. The
chart
> for the motor can be found here (it's the N 20 3451):
> http://www.clickautomation.com/PDF/items/MAE%20Express%20NEMA%2034%
> 20Step%20Motors.pdf When the chart lists steps, is that full 1.8
> deg, .9 deg, or micro steps?

First, good work on looking for a motor with a torque curve. Without
this curve you are only blindly guessing if it will really work.

Hmm, looking at that chart I can see your problem. It isn't
labeled. But most of the time the charts are full step and sometimes
show full and half step. Usually there isn't too much difference
between full and half step. Full step is usually worst case and I
would think that is what the chart is in.

For your application you would use the 60 volt curve. Gecko drives
can handle 80VDC max.

The oz-in on the vertical axis is straight forward but look closely
at the horizontal axis. It is in steps per second (telling me for
one thing that the chart is full steps, otherwise it would say
half/steps per sec). To convert steps per second to RPM take 1000
steps per sec / 200 Steps per rev = 5 rev per second x 60 = 300RPM.
For half steps the RPM would be + of this or 150RPM for 1000 half
steps. Working in full steps lets just make a quick chart.

200 steps/Sec = 60 RPM = 850 oz-in
400 steps/Sec = 120 RPM = 850 oz-in
600 steps /Sec = 180 RPM = 700 oz-in
800 steps /Sec = 240 RPM = 566 oz-in
1000 steps /Sec = 300 RPM = 480 oz-in
2000 steps/Sec = 600 RPM = 270 oz-in

I would say your usable RPM range is up to 300 RPM. Now we can
calculate your maximum speed the head can move. 300RPM x .1" lead =
30 IPM or 30 inches per min.

My father is handling all the
> electronics for this project; I'm doing the more mechanical side,
> though that is a bad reason for why I don't know much about micro
> stepping. Our needs overlap in the area of motors, I know how much
> torque and what speeds I want everything to move at, he knows what
> drivers we're using (Gecko, I think that limits me to what, 10A and
> 80V?)

Gecko stepper drivers can run up to 80VDC at 7Amps.

I'm not dead-set on that particular motor, it's just one I
> found that was cheap and had a torque curve.
> William

Well now you can make your decision on whether this motor is suitable
or not for your application. And you have the tools to use any chart
now for motor specs. And calculate RPM and IPM.

Wally






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