Re: formula ?

Hi Ballendo,

I really did just make an experiment.

the manual set-up that I ran for years would see table travel with
less than 5 pounds of weight on a string and a pulley. Actually more
like 3 pounds.

Now for this test, I can put a bucket on a string and fill it with
water. and since I need to pull on the leadscrew (too thin to push)
I can run the table and lift the bucket.

Assuming the most power if available at low speeds, I should be able
to lift quite a large weight.

one thing I have not done. (Seems once you exceed your spec's you
stop checking)

If I run these VEXTA (5v 1.5a) NEMA23 steppers on a Gecko running at
around 65 volts, I should be able to exceed 5,000 Torrecelli pressure
on the leadscrew and although it may only be about 0.01 Poncelet, it
should lift a 3 slug bucket at around 0.05 knots.

So my question is really basic. Since I can only lift a 3 slug
bucket 0.003 Furlong, do I just repeat with additonal weight until
the stepper starts missing steps? or do I need to use the higher
power, slow steps and not try for a higher speed? Or should I do
both and see what I can get out of high speed and low speed in
seperate trials?

At this point I am glad you asked. Since I will be switching to a 1
inch leadscrew haveing this set of data will allow a valid
comparrison with that new ACME screw.

questions, questions.

Dave

--- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:
> Hello,
>
> And don't forget to de-rate that figure by the friction of your
12/13
> allthread drive...
>
> Maybe 30% efficient (if that), so now you're at 153 lbs. Hmmmmm...
>
> You know, I'm a bit in favor of the "Mariss" approach myself; that
is
> to use an experiment in addition to the calcs.
>
> I wonder what the "real world" result will be if you put a "fish
> scale" on the driven part of your system... Run it slow, and let us
> know, please. (I'm guessing less than 100 lbs actual)
>
> Okay, that might be a big fish scale<G> but even some workout
weights
> and a rope and pulley will give us some idea of where "reality" lies
>
> Hope this helps,
>
> Ballendo
>
>
> --- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> > dave_ace_me wrote:
> >
> > > Hi Jon,
> > >
> > > great explanation. I couldn't get the concept that the lead of
> the
> > > screw was part of the circumference part of the equation.
> > >
> > > OF course that makes sense, a 1/2-5TPI 1/2 screw or a 2"-5tpi
will
> > > still move the table one inch for 5 revolutions. so the actual
> > > diameter or circumference of the screw is not important.
> > >
> > > I noticed that we rate steppers in oz/in but power in inch/lb.
> > > Can I assume that 16oz/inch is the same as 1in/lb?
> >
> > I believe this is correct. There are so many torque measurement
> units, its
> > a mess. N-M, N-cm, gm-cm, oz-in, lb-ft, .........
> >
> > > That would make a 50oz/in stepper 3.125 inch/lb. Fits close to
> your
> > > 10 inch /lb value. Yours seems to be 150oz/in.
> > >
> > > so my 50in/oz at 2:1 is 6.25 in/lb on the leadscrew. The 13tpi
> > > (0.0769"circumference/0.02448dia/0.012243radius) then 6.25 /
> 0.012243
> > > = output force
> > >
> > > 6.25 / 0.012243 = 510 pounds of force. That kind of force
will
> bend
> > > the noodle of a leadscrew I am using.
> >
> > Yup, sounds good. but, remember, stepper ratings are good at
zero
> speed,
> > only. They drop off very rapidly as speed increases.
> >
> > Jon