High-quality 3-phase inverter drive methods for turntables (rectangular waveforms)

[newvirus2008]

...I have used these motors to replace both the Premotec and Thorens with excellent results. When driven by a 3 phase sine wave drive there is very good torque with little vibration, certainly a lot smoother than either of the original motors.

The driving waveform suitable for a motor is determined by the shape of the back emf generated by it. For example, the methods shown in this thread are meant for true synchronous (open loop) operation of motors with sinusoidally-distributed stator windings, that often result in sinusoidal back-emfs.

http://www.vias.org/feee/c13_motors_08_02.html
http://www.ece.umn.edu/users/riaz/animations/3phasewdgs.html

However, the term BLDC has become very common these days and some motors labelled 'BLDC' might actually have sinusoidal back-emf like PMSMs. This maybe easily verified by running the machine as a generator at constant speed and checking its generated voltage waveform on an oscilloscope.

 

[ralphfcooke]

I've just tried testing the back emf of one of my Nidec motors, here's the result.

Combined with 'oilite' sleeve bearings, these motors do look pretty good.