Re: Servo disk motors for rotary spark gaps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

So basically they are overgrown basket wound motors, like Maxon makes. I
still don't see a reason to pick one of these for a spark gap over any other
sort of motor, unless you have these laying around. A spark gap is not a
legacy tape drive or check processing equipment and does not need instant
stop/start abilities.

I've tried for fun to mimic an 1800 rpm synchronous AC motor with a DC
motor, PWM drive, radio shack potentiometer and regulated power supply. The
AC motor was replaced with the DC one and spark gap left alone otherwise.
Surprisingly, with no feedback other than my eye, it was almost boringly
easy to maintain 1800 RPM dead on like the AC motor. Things would drift
after about 10 seconds or so, clearly even the junkiest servo system with
even a one if not a few counts per revolution sensor would be sufficient to
control a DC motor in fake sync mode.

KEN

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Monday, June 02, 2003 7:34 AM
Subject: Servo disk motors for rotary spark gaps


 > Original poster: "Scott Hanson by way of Terry Fritz
<teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>
 >
 > Ken -
 >
 > How long does the first revolution take, from a dead stop? Literally
 > milliseconds, depending on the size of the motor. Because the armature
 > consists only of a very thin disk of copper conductors, with absolutely no
 > iron core or laminations of any sort, the armature mass is a tiny fraction
 > of the mass of any conventional AC or DC motor. In fact, the motor shaft
 > itself can have more mass than the rest of the armature.
 >
 > Also, because of the lack of discrete iron poles in the armature, these
 > motors have almost no "cogging" at low speed. The lack of iron means no
 > inductive spikes during commutation, and no arcing or burning of the brush
 > and commutator surfaces. These motors require only very small brushes and
 > commutator surfaces. A 1/2 HP motor of this type has tiny brushes, and
will
 > run with hydraulic smoothness at only a few RPM with only 2 volts applied.
 > During full acceleration they can draw 50A or more.
 >
 > Lots of these motors are now available on the surplus market, and many of
 > them are equipped with high resolution optical encoders for precise speed
 > control.
 >
 > These encoder-equipped motors could be used with an external feedback
 > control circuit as an "electronically controlled" synchronous rotary spark
 > gap motor, as opposed to a modified (salient pole) induction motor that
 > achieves its synchronism internally via "electromagnetic control".
 >
 > Regards,
 > Scott Hanson
 >
 > ----- Original Message -----
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Sunday, June 01, 2003 3:43 PM
 > Subject: Re: Need a variable-speed 2hp or greater AC motor for serious gap
 > drive
 >
 >
 >  > Original poster: "Crow Leader by way of Terry Fritz
<teslalist-at-qwest-dot-net>"
 > <tesla-at-lists.symmetric-dot-net>
 >  >
 >  >  > Original poster: "Scott Hanson by way of Terry Fritz
 >  > <teslalist-at-qwest-dot-net>" <huil888-at-surfside-dot-net>
 >  >
 >  > [cut]
 >  >
 >  >  > Also, there are large number of high-performance, ironless-core DC
 > servo
 >  >  > motors (Servo Disk type) on the surplus market now (ex-computer tape
 > drive
 >  >  > or large disk drive) that can accelerate from a dead stop to over
5,000
 >  > RPM
 >  >  > in less than 1 revolution. This type of acceleration can destroy
 >  > couplings,
 >  >
 >  > How long does this first revolution take?
 >  >
 >  > KEN
 >  >
 >  >
 >
 >
 >