Re: spindles powered by REGULAR AC induction motor

Hi,

That reminds me of the of the first "supersonic" step motor I
encounterd.

There was a time that Escap was promoting its disc step motors. These
were size 34 step motors that used a ceramic magnet discs for the
rotor, generally inferior motors but they did feature very low
inductance.

Because of the low inductance and very low rotor inertia these were
very free reving motors, so I decided to find out just how fast they
would go.

I was using a precursor of the G201; a drive that was eqipped with an
opto that would pass 5 MHz, but in all other respects like the
present drive.

I accelerated the motor to 240,000 full steps per second when BLAM,
the motor jumped 6" on the bench and seized.

I autopsied the motor, the ceramic rotor was gone. All that remained
was ceramic sand and deep gouges (1/8") in line with the plane of the
former rotor in the aluminum housing.

Working things backward afterwards, at that speed the tangential
velocity of the rotor reached 1,100 fps, or the speed of sound.

Maybe I like to think I heard a sonic boom just before the motor
blew. Can't be sure though.

By the way, that's 72,000 RPM. Who says steppers can't go fast.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, Jon Elson <jmelson@a...> wrote:
>
>
> Carlos Guillermo wrote:
>
> > Peter -
> >
> > I regularly take my Bridgeport 1720-rpm motor to 150%, but I have
> > no idea what the limit is. I'm also tempted to take a smaller
> > motor and crank it slowly up to 600% speed to see what happens.
> > (I'll take Jon E's approach and hide under the bench, of course)
>
> While overspeeding a 1725 RPM motor up to 200 % is not likely to
> cause an "uncontained disassembly", (as the jet engine manufacturers
> call an "engine explosion"), taking any motor to 6 times its rated
> RPM sounds pretty dangerous. A 1725 RPM motor would reach
> over 10,000 RPM and a 3450 would go over 20,000 if they could
> follow the frequency. Since most inverters go to constant voltage
> about 100%, the motors would lose rotor excitation and level off,
> or possibly spin down and just stop when driven much above 200%
> but only 100% voltage. If you had an arrangement (like a
transformer)
> to supply 6 x voltage at 6 x frequency, then the motor would either
> have an insulation breakdown, or the dreaded uncontained
disassembly.
> The latter, you DON'T want! I'm not joking, a bench won't save
> you, unless it is more like an armored bank vault! Bursting the
> rotor of a modest 60 Hz 1/2 Hp or so motor at 10 - 20 K RPM
> would be something like setting off an artillery shell inside your
house.
>
> Oh yeah, there was a story in the paper about two years ago. An
> aircraft instrument technician in the St. Louis area was killed by
an
> aircraft gyroscope that blew up! I'm guessing he fired up a 12 V
> gyro on 28 V by mistake, and it overspeeded! Now, this thing has
> a rotor weighing about a pound, and it was presumably only going
> twice its rated speed!
>
> Jon