Help with Shugart SA801 8" floppy with 230v 50 cycle motor...

[Tony Duell]

> I suspect there might be a reasonable degree of commonality in small motor 
> designs, but I think you're right - there's no guarantee that all small motors 
> of a given design voltage / frequency will run at the same speed... (at least, 

No, there isn't, but equally, you can't get just any speed you like.

Given that there has to be an even number of poles, you are limited to 
motor speeds which are of the form 3000/n (n an integer) on 50Hz mains 
and 3600/n on 60Hz mains. This is for a synchronous motor -- an induction 
motor will run a little slower, there has to be some 'slip' between the 
rotating magnetic field in the stator and the mechanical rotation of the 
rotor to cause the necessary current to be induced in the latter. For 
example, a 4 pole synchronous motor (on 50Hz) will turn at 1500rpm, an 4 
pole induction motor might turn at 1425 rpm or so.

> alternator frequency is dependent on RPM and pole count, so the RPM for a 
> motor is presumably dependent upon frequency and pole count)

Of course. It's pretty obvious why when you think how these motors 
actually work.

-tony