Re: Rotatry Gaps motors

Tesla List wrote:
> >From rodney-at-johnxt7.anu.edu.auMon Jun  3 22:26:39 1996
> Date: Tue, 4 Jun 1996 08:35:13 +1000 (EST)
> From: Rodney Davies <rodney-at-johnxt7.anu.edu.au>
> To: Tesla List <tesla-at-poodle.pupman-dot-com>
> Subject: Rotatry Gaps motors
> Hi all,
> I was talking to a couple of friends of mine in Canberra about motors
> used for gaps, and was pointed out a rather important thing.
> If the motor is running under synchronous, the coil should
> experience "spluttering output". Our mains power works at 50Hz here,
> therefore our synchronous speed is 1500rpm. The way I've been told to fix
> this problem is by grounding 4 flat edges (about 1/4" deep) onto the
> rotation shaft of the motor. The motor should then, as it is approaching
> the synchronous speed, make a "lock in" sound. This should then set the
> coil running with a continous output.
> Has anyone else experienced problems like this?

> Comments? Suggestions?
> See ya's later...
> Rod

  My small (3KVA) coil uses a modified 1750 RPM (60 Hz) motor running
synchronously at 1800 RPM. Indeed, to get synchronous operation, you
cut four 'flats' on the armature to provide 4 phsycally defined
magnetic poles. However, the depth of the flats are important. If you
do not cut them deep enough, the magnetic poles will not be adequately
defined, and the motor may or may not lock in. If you cut them too
deep, the motor will loose a great deal of it's power.

  Incidentally, this same technique works on 3450 RPM motors as well,
only you cut two flats instead of 4.

- Brent Turner