excellent basic motor info

[Boltz]

Hi, I found this link, and when it comes to motor types and control I think it's the best info I've found yet...

http://openbookproject.net/electricC.../AC/AC_13.html

However, I am a complete and total NOOB, so if somebody who *does*, in fact know a lot about motors could take a peek, I would appreciate it.

I'd been having some trouble grasping the difference between brushless dc (trapezoidal back EMF) and brushless ac (sinusoidal back EMF), and I think I've finally got it.

Still trying to figure out why Multicam chose 8-pole motors instead of 6-pole for my machine.

-Jim Hart

[Al_The_Man]

Here is a good link that shows BLDC commutation.
http://users.tinyworld.co.uk/flecc/4...otor031102.swf
The difference is that in a BLDC two phases or conductors are fed at a time, simulating a DC motor turned inside out. The 3 phase sinusoidal has current fed to all three conductors phase shifted at 120 electrical degrees apart.
An 8 pole motor is superior to a 6 pole in that there will be 4 electrical rotations per mechanical rotations in a 8 pole compared to 3 in a 6 pole.
In spite of many concerns that a BLDC possess coarse positioning at low rpm, I am using them with a Galil card direct drive to a B.S. with 2500p/rev encoders and can position within one pulse.
Al.

[Boltz]

Okay, so if 8 pole is superior to 6 pole, how come they're so rare? Everything I see is 6 pole.

-Jim Hart

[Al_The_Man]

I wouldn't say they are rare, just depends on the brands you are looking at.
I am using Tamagawa, Applied Motion, and converted Fanuc servo's, all 8 pole, as well as Mitsubishi also.
Al.