Re: Why gecko drives don't support DC brushless servo ? do they ?

Thanks Jon, for your detailed information. I wish to minize the
efforts needed to enjoy the power of CNC machining, so in the
beginning it is better to be heading in the correct direction. So
the final decision is to get start from Gecko drives and DC brush
servos.

Regards,

Horace

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:
>
> Horace, T.L.Ho wrote:
>
> >Gecko G320 G340 all said they are for DC brush servo motor. Why
can't
> >they be used to drive DC brushless servo motor ?
> >
> >
> >
> So-called DC brushless motors, like on computer fans, only go one
way,
> and have
> elctronics in them to commutate the coils in the proper sequence.
So, they
> are not reversible, and not designed to go at low speeds.
>
> Permanent magnet brushless servo motors have been called by many
names.
> They used to be called DC brushless, but this caused confusion,
because they
> are NOT actually fed DC. In truth, they are permanent magnet
synchronous
> AC motors. The generally have three phases, and therefore the
motor has
> three power wires. This should be the first clue that you can't
hook
> them to
> a Gecko 320/340, which provides motor power on two wires.
>
> Since the motor drive is required to do the commutation for these
> motors, the
> drive needs to know motor shaft position. This is generally done
with 3
> Hall-effect sensors built into the motor, or sometimes in the
encoder.
> (There are also sensorless drives, and other drives that integrate
the
> commutation
> signals with the encoder signals in non-standard ways, like
Yaskawa.)
>
> The typical brushless servo motor therefore has 3 motor leads and
usually
> 5 hall sensor leads (3 signals + power and ground). This does not
> include the
> encoder signals.
>
> It would be theoretically possible to build an outboard
commutation
> controller
> that could adapt the Gecko 320/340 for brushless motors. it would
have
> 6 power transistors and control logic, and be approaching the
complexity of
> the Gecko itself. Some motors were made like this for specific
> retrofits with
> existing motor drives until the brushless drives were available.
>
> Rutex makes a line of brushless drives, as well as Copley. AMC
sells a line
> of Copley drives under their label.
>
> Jon
>