Hybrid Connectors Was Re: availability of composite multiconductor cable?

> The real problem is unfiltered PWM outputs on commodity motor

drives.

> I have had no problem with noise on the encoder or tach signals on

my

> servo system. But, I put a very effective output filter to remove

the

> high energy pulses on the PWM output to the motor. (I used shielded
> cable for the tach and encoder, anyway.) but, I run all the cables

parallel

> without any problem. Probably you can't do that with Gecko or Rutex
> drives.
>
> I used round circular plastic connectors from AMP. They have a

large

> choice of these in the Digi-Key catalog. I used some 27 pin

connectors

> with all the same size pins, rated at 5 Amps/pin. But, they do

have some

> with wide blade-like contacts in some positions, so you can have big
> ones for the motor and smaller for encoder, limit switches, etc.
>
> Jon

I took a clue from the commercial units I have seen (and salvaged for
parts) and decided to mount the motor drive (Gecko340's) cards in
close proximity to the motors they drive on the machine. This did
several things to reduce noise. The encoder signals run 5 inches on
unshielded wire. The 60VDC for the Gecko's is filtered before and
after the trip up to the driver cards so no nasty high current PWM
runs down long wires. The wires between the GECKO's and the motors
are #16 twisted pairs; once again about 6" long (unshielded). The
step and direction signals are buffered in the controller cabinet by
a Sound Logic Card and travel up the same bundle as the DC feeds and
the table limit switches. They are the only wires that are shielded.
One big AMP military style connector does all of the feeds.

Since the inputs to the Gecko's are opto isolated they have a fairly
high level of noise immunity provided the driven end is low
impedence. Even running a high frequency arc-start plasma unit I
have no issues with false pulses, crosstalk or other noise related
issues. If you don't want to transmit noise don't build antenna
wires for high current square waves.

Something to consider.