[GreenKeys] Machine speed and VFDs

[Jim Haynes]

There's a thing called the "hysteresis synchronous motor".  If you look at
the motor in a Teletype machine you'll see that the speed is marked 3600
RPM and that the rotor appears to be a solid piece of metal.  It's been
a long time since I had to take the AC machinery course in EE school, and
I don't think that kind of motor was covered, but I can assure you it is
a real synchronous motor, not an induction motor that has some slip.