Vertical Machining Centre Retrofit with Chinese Servo Drives Build Thread (NZ)

hey tom

since you answered my other question so fast and since you have been doing this before I have another quick question here.

I am using step dir chinese servo drives and the drives are "smart" eg they close the loop with the servo motor/ servo drive loop.

these drives like most of yaskawa copies can output the encoder pulses to a external controller in my case mesa 7i76 spindle encoder input.
I have checked and the drive outputs standard 5 v differential signals suitable for the mesa to read.

my only question is how do i connect up at the mesa end. I have 3 pairs of differential signals from the servo drive. A B Z. Since this comes from the servo drive not a standard encoder I assume the signals get powered from the servo drive and I leave the 5v and ground unconnected on the mesa encoder inputs?

just a little bit stuck here. been trawling the forum for hrs trying to find a definitive answer

regards

Andrew

this is a general call for help now.

I am need some positive confirmation here about what I need to connect.

just to refresh everyone. I have 5i25 and 7i76 mesa cards. 7i76 is powered from a 24v dc powersupply for the field IO.

currently the jumpers are setup to supply the 7i76 5v logic power from the 5i25.

I am trying to connect this encoder signal from my servo drive into the spindle encoder input in the 7i76


as you can see the servo powers the encoder so I think I don't need the 5v from the mesa card.

Now what gets me confused is the grounding of everything.

question 1: Do I even need to use a ground with differential signals

question 2 if I need to connect the ground what in my servo drive do I connect it to?

I want to avoid any grounding loops and am a little confused

I will make up a big diagram soon showing how everything is connected.

regards

Andrew

1 No, just use the shield from the drive but do not connect the other side of it, meaning the shield is connected only to the drive, the Mesa side should not be connected to anything.
2 encoder shield.
And you will need another Mesa board, something like 7i85X , but not sure exactly, so someone else might chime in.

hey tom

so just to clarify

I already have the cable shield grounded to the servo drive connector case to reduce interference.

does that mean that I can just connect the 3 differential pairs up (so 6 wires in total and I am good to go) So the encoder differiential pairs don't need a ground also?

and also what about the 7i76 logic 5v power from the 5i25? will that be ok for now as is. I know eventually I will need to get a separate 5v powersupply so I don't put too much load on the pci slot with 5 encoders running..

All I want to do for now is connect each axis up in turn, to the spindle encoder in the 7i76 and then use the encoder feedback in halscope to know what I need to set the Pid loop in the servo drive to. then I will remove the feedback and tune the next axis and so on...

I should have a 7i89 mesa card (this has 5 encoder inputs on it) coming asap once I can get it shipped from america. and I will get a 7i84 also for some more IO pins as I need about another 20 IO pins for buttons and such.

regards

Andrew

Becksvill wrote:
does that mean that I can just connect the 3 differential pairs up (so 6 wires in total and I am good to go) So the encoder differiential pairs don't need a ground also?

Yes.

Becksvill wrote:
and also what about the 7i76 logic 5v power from the 5i25? will that be ok for now as is. I know eventually I will need to get a separate 5v powersupply so I don't put too much load on the pci slot with 5 encoders running..

The encoders are powered from the drive, so no load on the Mesa boards for that.
And that combination of Mesa cards should do just fine, just do not forget to order a cable with headers for the 7i89.

thanks Tom

Ok I will try that tomorrow and report back.

then I will go through your wonderful servo tuning tutorial and try to work it out without too much hand holding

and then I better get some more photos up here:)

regards

Andrew