> > 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. 


Servos also don't lose torque at speed, the faster you drive a stepper, the
less torque it has.  

Steppers aren't all that accurate anyway, (just because it says 1.8 degrees
per step doesn't mean it moves exactly 1.8 degrees), but they're close
enough for most jobs since the error doesn't accumulate.  Microstepping
improves things a bit.

Steppers are much easier to control, a driver can be as little as 4
transistors and PIC 508.

Tony

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