Ethercat Latancy

Hi Guys,

Not sure where to post this,

When using Linuxcnc as a ethercat master, Does latency of the hardware it is running on become a factor?

I know with say ethernet breakout board you can get away with a bit of latency due to step generation being done on the board rather than through the software,

But since Ethercat is processed through the software is it dependent on the Latency of the hardware or because it is only sending out packets of data for the slave devices to read latency is not a issue?

Thanks Tom,

My understanding is that the Linuxcnc system is that motion controller or ethercat master, I hope someone can clear that up for me.

LinuxCNC requires real time (low predictable latency) and ability to meet the thread
invocation rate for the servo and possibly base threads. This requirement is
independent of the type of external hardware. Smart external hardware typically only
uses the (slower) servo thread so its easier to meet the latency requirement than simple hardware
(GPIO or parallel port) that requires a base thread to generate steps/read encoders etc etc.

Good day.
And what is the recommended maximum value for the latency test? To make the servo drive work properly?

My lineup:
MB: H81M-P33
drivers: ASD-A2-0721-E

  The latency test shows around 18,000 ns for the servo thread. Is it high value?

Thank you for answer.

Thank you for your response.
So do you think the EtherCAT servo won't hiccup?
I tried it on ASRock A320M-HDV R3.0 and there was a problem (drives hiccupseed).
But on ASRock A320M-HDV R3.0 the latency was 40,000 ns.
That's why I'm afraid.

Thank you very much.

For Ethercat latency,

There is a difference between using servo's (pid) or steppers (pulse).

When using steppers, you can use a ethercat stepdrive 50v 5amp. I don't recommend the usage of the bechhoff stepdrive's because of cost's and power. Usage of chinese drives 80v 8amp's give more power if needed, cost's are less.

This will result the step pulse generation is done by linuxcnc. If you compare the parport output with a ethercat output. The parport
can move your machine for example max : 12000mm/min, the ethercat will do it max : 20000mm/min.

Setting up the ethercat steppers can be quite difficult, but i have examples that will work quite good.

For servo's, the servo drive will only go to a position. The drive get's PID (destination info from linuxcnc) and will go there..

I will use servo's (pid). Delta driver ASDA A2-E and 750W Delta servo motor ECMA-CA0807RS with absolute encoder.
Is it difficult to switch servo to position control?
Sorry to ask stupid questions.

It is a pity that this list is not updated.
wiki.linuxcnc.org/cgi-bin/wiki.pl?FixingSMIIssues
Or do you know about a more current list of chipsets?

Very thanks

If you use delta servo's you can find existing examples on the net with google. I have seen them in the past.

I never used servo's on ethercat, but you can put the ethercat cable into the servo drive if the drive is ehtercat compatible.

An other way is to use the step-dir signal on the servo drive if available. (works good, but ethercat straight into the servo drive is nicer).

If you use pid, you don't have to worry about latency. Use the hybrid debian with linuxcnc, you can download it at this site.
Debian is basic, but very stable, with nice performance.