Re: [CAD_CAM_EDM_DRO] Long cables for Gecko G340s

andy@... wrote:

> Turned out I needed longer cables for one of the axes of my flame
> burning conversion and I am running into Tom Eldregdes problems as
> covered in this and other posts.
>
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/message/27064
>
> I am confused about what I need to get this running properly.
>
> Can anyone summarize what is needed. The posts mention:
> 1. Ground the motor shield at the case.
> 2. Add a small capacitor to the encoder?
> 3. Don't ground the enconder shield?

Tom can probably give you more precise details, but the gist of it, as
i remember, was :

1. make sure the plasma torch doesn't connect at any point to the rest
of the machine. (I guess he workpiece is connected by a ground clamp.)

2. If possible, insulate the motor and encoder from the machine frame.

3. Connect at least a .1 uF capacitor across the +5 V power and ground
wires on the encoder.

4. ground both the encoder and motor shields to the ground point on the
servo drives. now, this can be tricky, finding the best point for this
ground.
These shields can be bringing significant noise currents back to the servo
drives, and you need to drain them off safely to a true ground, rather than
inject that noise into the computer signals going into the drive. Marris
would
be the best person to advise here.

Comment to your # 1. Grounding the motor shield at the MOTOR case
(you are not clear about which case you are talking about) sounds bad,
unless the motor is grounded to a good, quiet ground point. If the motor
is floating in a high noise environment, or connected to a noise source
9the machine frame) then it will couple that noise into the motor wires.

Comment to your # 3. (I think Tom found this to work, but it sounds quite
poor practice.) Having a floating shield is worse than no shield. Tying
the
shield to a high quality ground point on the device that senses the signals
is generally the best technique. If there is a separate ground for the
encoder
power output, or a ground for the +5 V power on the servo drive, that would
likely be the place to tie the shield. The motor shield may have a lot of
PWM
carrier on it, and so needs a place to dump that energy. The main motor
power
ground would be a good place for that, in general.

Jon