[syntheticlight (OP)]

Hello all.

I have a house fan running in my room. Earlier today it ground to a halt - i opened it up and took it apart in the hope that i might be able to fix it (i could).

I'm no mechanic nor engineer (maths student), so my terminology will be bad. I noticed that the drive shaft (the metal rod, at the end of which is the fan, right?) turned via an electro-magnet.

[diagram=385_0]

Item 2 is a side view of the thing which slides into item 1 (which is a cross section of a cylinder thing). The little white bits around the inner-diamater of item 1 are a beautiful representation of pieces which had been cut out of the metal. First of all - why is it designed in this way, with bits cut out?

Second of all, and my main question; since the thing turns perfectly well with these bits missing, is there a minimum amount of the inner diamater of item 1 which must remain intact for the system to work? Be it a percentage of the inner diamater, or a percentage of the surface area of the inner-area of the cylinder. My instinct tells me that it should run with maybe 3, equally spaced thin strips intact, with the rest lowered.

I'm hesitating to use the term "surafce contact" - for there is no contact whilst in motion, right? Like those maglev trains.


Apologgies for my horrid drawing skills and ineffective descriptions. Hoping someone knows what i mean.

Thanks.

[RD]

The cut outs could be for the windings: the coils of wire which produce the magnetic field.

 [ Invalid Attachment ]

http://en.wikipedia.org/wiki/Induction_motor

[syhprum]

I think that the most likely type of motor to drive a small fan would be a single phase shaded pole type where a suitable phase shift in the magnetic field to produce rotation is produced by a shorted single turn winding on the stator.
The slots in the rotor carry single shorted turns that react to the rotating field generated by the stator, you could make a motor with only these windings on the rotor and no magnetic materiel but it would be very inefficient.
I notice that the three phase motor the illustration of which RD has supplied uses no magnetic materiel in the rotor, this is purely diagrammatic no real life motor would be built like this.