Re: Servo controllers for table top machines.

I know what you mean.:-) I really mistrust "magic numbers" unless I
know where they come from. That's why I "roll my own".

Start with the 2 definitions for power:

746 Watts = 1HP
1 HP = 550 ft-lbs / sec

Imagine a motor that has a 1-foot radius winch with a cable wound on
it supporting a 550 lb weight.

What RPM must the motor turn at to lift the weight 1 foot per sec?

> RPM = 1 / 2*pi = 0.159235 revs/sec = 9.554 RPM.

What is the torque on the motor?

> 550 ft-lbs = 105,600 in-oz

What is the motor power?

> 1HP = 746 Watts

Since power equals RPM times torque then:

> 105,600 in-oz * 9.554 RPM = 746 Watts
> 1,008,902 = 746 Watts

> or Watts = RPM * in-oz / 1352

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, John Dammeyer <johnd@...> wrote:
>
> Hi,
>
> I'm always a bit confused when I see magic numbers without the math
behind
> them.
>
> So here are the conversions,
>
> From http://www.zeroggraphics.com/Portfolio/Torque-Conversion-Chart.pdf
>
> 700 oz-in is the same as 3.64 ft-lbs
>
> From http://en.wikipedia.org/wiki/Horsepower
>
> HP = Torque (ft-lb) * RPM
> ---------------------
> 5252
>
> So we have 3.64 * 500
> ---------- = 0.347HP
> 5252
>
> Also from the same link,
>
> 1 HP is equivalent to 746W
>
> Therefore 746W/HP * 0.347HP = 258W
>
> John Dammeyer
>
>
> > Subject: [CAD_CAM_EDM_DRO] Re: Servo controllers for table
> > top machines.
> >
> >
> > > I was under the impression I could just bolt on the brush type servo
> > > motors directly to the ball screw end, similar to the way my stepper
> > > motors are connected currently.
> >
> > No... You can't (unless you're looking to burn your brand-new
> > servomotor down in 5 minutes or less).
> >
> > Rule #1: Servomotors are not step motors.
> >
> > --------------------------
> > Typical NEMA-34 step motor: Develops 700 in-oz of torque out to 500
> > RPM for a power output of 260 Watts. The motor gets too hot to touch
> > (perfectly normal) at 7A and 80VDC.
>
> >
> > Mariss
>