Re: stepper vs. servo

Ray,

A bit more:

A stepper is just a syncronous motor run using square waves (At the
fullstep resolution). In other words, the square waves are as close
as you can get to a sine wave using only on and off.

When you go to 1/2 step, you add another level of current control,
and the input waveform gets another step, and is a little closer to
the sine wave ideal. As you go up in microsteps, you keep refining
the input waveforms by adding steps/levels towards ideal sine waves.

At some point, you're back running a synchronous motor with sine
waves...

Ballendo

P.S. Our typical steppers will run just fine at 72 rpms, using a
capacitor on one coil, and fed by 60 cycle ac. (infinite
microsteps<G>)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Raymond Heckert" <jnr@a...>
wrote:

> Has anybody ever designed a micro-stepping driver that outputs
> approximations of sine/cos to two adjacent coils. I understand

that you

> develop max torque at any rpm, up to the max (which is higher than

the

> square-wave input). Is this true? How much would it take to

develop,

> assuming no one already has? BTW does anybody know anything about

Don

> Lancaster's (tenaja.com) Magic Sine Waves, and if they can be

applied to

> this application.
>
> RayHex
>
> ----------
> > From: Jon Elson <elson@p...>
> >
> > Given the Gecko 320 as the driver for the servos, I think there

are a

> > couple of significant advantages over steppers. First, the

servos are

> > usually capable of a greater speed range, while steppers rapidly

lose

> > torque at higher speeds. With servos, you rarely have to worry

about

> > resonance issues. You don't say whether you will use belts, rack

and

> pinion
> > or leadscrews to drive this machine, but the servo will likely

provide

> > smoother motion, and be less perturbed by some backlash in the

mechanics.

> > Steppers can go wild when rack and pinion drive is used, and

rattle the

> > gears
> > something awful. Finally, if you lose a step with a stepper

drive, you

> > won't know it until you measure the finished part. With the

gecko 320,

> > it won't allow small errors to build up, and will fault if the

drive

> binds
> > up or crashes. This can be sensed by the computer and cause it

to stop

> > all axes.
> >
> > Jon