> > > For controlling position I believe you are thinking of what's called a
> > > "stepper" motor. It is also "brushless", but has many more poles
> > > allowing for relatively precise positioning.
> > 
> > Servos in HDD are also "brushless", position quite precise under PID.
> 
> Very true, but I wouldn't consider them "motors" per se, which is what
> the thread was about.
> 
> A brushless motor isn't very good for positioning since it doesn't have
> a great deal of "holding power" at stall. I'm sure you could devise some
> PID system to turn a brushless motor into a pseudo servo, but frankly a
> stepper is just so much easier I don't really see the point.
> 
> TTYL

Sorry, I can't see your logic here. Most (all?) modern CNC machining centers use brushless motors to drive the ballscrews. Holding a 10,000 pound part against a 5k rpm cutting tool driven by a 30hp motor and maintaining 0.0002" accuracy is certainly one of the more demanding positioning applications I can think of.
http://www.haascnc.com/details_HMC_HS.asp?ID=37#HMCTreeModel

Of course they cost ~$0.5Million. 

-Denny



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