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

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