Re: Gecko G420's question

David Eldredge writes:

"Gentlemen," -- loosely speaking in my case

"Does anyone know what type of feedback the G420's are
expected to use?
Hall effect or encoder?"

As I recall, they are Hall with encoder. In my
collection of drives and motors there are: Halls,
Halls with encoders, Halls with encoders with some
kinda absolute track, encoders with simulated halls,
and resolvers.

When you use Halls with encoders, there are two
approaches. The first is to commutate the motor as if
you just had the hall signal and use the encoder to
keep track of your error. In this sense, the drive
doesn't know if the Hall is about to signal to go to
the next phase or not, it just does the commutation
with the feedback. My guess is that this is how the
Geckos will be. Other drives require that they know
the encoder counts and then use sinusoidal
commutation. I like to think of a brushless motor as
a stepper motor with a very small number of steps per
rev, even though Mariss says it's not true. You can
get them to step, but you will hate yourself in the
morning. The way I look at it a stepper motor
requires commutation, a dc motor does it thru
mechanical means.

"Will the G420s save money on servo motor cost? I
understand the
benefits of eliminating brushes and commutators, but
are there many sources
of motors for them? "

Brushless took over the machine tool and robotics
market sometime in the mid-1990's and thus they are
the wave of the future. Ebay has a regular supply of
brushless motors. I would say that high quality
brushless motors are more numerous on ebay than high
quality dc motors, but I don't really look that hard
for the DC motors. New brushless motors cost at least
$500, but all the other options are also
breathtakingly expensive if you buy them new retail.

I skip the question about making them.


"How about some more discussion on what this new
development will bring
to the hobbiest CNC guy."

The Gecko drives make brushless motors available to a
person that just wants to go out and buy a drive. The
competition costs $500 - $1000. The motors rarely go
for more than $100 on ebay, and almost never go for
more than $200. Obviously, it's still high end, and
it is considerably more involved subject than DC
motors or steppers.


Eric




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