Re: good results and sync gapsl

From: 	Peter Electric[SMTP:elekessy-at-macquarie.matra-dot-com.au]
Reply To: 	elekessy-at-macquarie.matra-dot-com.au
Sent: 	Sunday, August 10, 1997 5:55 AM
To: 	Tesla List
Subject: 	Re: good results and sync gapsl

> Peter,
> In order to use a DC sync motor, you would have to build a speed
> and phase servo circuit using speed and phase feedback to control
> the motor.  I was thinking of trying this...the advantage is you could
> control the phase of the sync-gap electronically rather than needing
> a mechanical phase adjustment device...but it's still probably easier
> to just use an AC sync-motor.  (I don't know if these hard drives have
> a a built-in servo?)
> BTW, you can modify a regular induction motor to create a sync-motor
> by grinding two flats onto the armature of a 3450 rpm motor, or 4 flats
> onto a 1740 rpm motor.  (if you have 50Hz AC, these rpms will
> be different...2950, and 1450 rpm, I suppose).  The flats can be ground
> using a milling machine, or by drilling numerous holes into the area to
> be removed, and then filing (use a large file) the excess away.  It's a
> lot of work if you do it by hand...but it can be done.  The two flats
> should be parallel, and of equal size to keep the motor balanced.
> You'll have to use a larger motor than normal because the modification
> causes the motor to lose some of its power.  I am able to use a 1/10HP
> motor because I'm using a small, light rotor, but if you're using a heavier
> rotor, you may need a 1HP motor.   The flats should be 1/2 as wide as
> the armature dia for two flats, 1/3rd the dia of armature for 4 flats, if I
> remember correctly (I have this written down somewhere from when
> I did my experiments).  Be sure not to cut 4 flats onto a 3600 rpm
> motor...you'll lose too much power...and the depth of cut will be very
> critical.
> Coiling for today and tomorrow,
> John Freau

John, thanks for the detailed info on modifying induction motors. I may
have a go at this if I get some time. Some years ago, I used to travel
to various overseas countries fixing Telex machines amongst other
things. They all had a beautifully made 1/2 HP synchronous motor in them
and we threw out dozens of the things over the years. If only I had kept
a couple...

Cheers, Peter E.