Stepmotor vs brushless DC servo

On Fri, 17 Aug 2007 23:11:13 +0000, Everett X. Wang wrote:


I prefer to use commutated (regular DC, or brushless with appropriate
sensors) motors for highly inertial loads. With steppers you either have
low enough inertia that you can just start stepping, or you have to ramp
up you acceleration.
 The problem is that this ramp has to be completely open-loop -- and I'm
never happy with that.

So if it were me, I'd go with the brushless motors.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
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Tim Wescott wrote:

A stepper tightly coupled to an encoder with as many steps as the motor
(or a multiple of that) can be driven just like a brushless motor with
Hall-effect switches. the dividing line is a bit arbitrary. Bypass the
hall effects, driving the coils directly from logic and a typical
brushless motor can be driven like a three-phase stepper.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

On Fri, 17 Aug 2007 23:24:28 -0400, Jerry Avins wrote:


Granted.  But then you're back to something commutated.  It solves the
problem at the cost of more complexity, which is exactly what I was
recommending.

Out of curiosity: have you done this?  I can see how it would work, but
you'd pretty much need a microprocessor with some clever start-up code.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html