MESA stepper cards.
- Moronicsmurf
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11 Jan 2017 19:48 #85621
by Moronicsmurf
MESA stepper cards. was created by Moronicsmurf
When running a stepper card like the 7i76E or the 5i25+7i76
What latency value is the important one.. Base thread or Servo thread??
Cuz i'm thinking that the latency shouldn't matter to much if you run an external card - guessing im asking you really need a crazy good latency value when running mesa boards?
What latency value is the important one.. Base thread or Servo thread??
Cuz i'm thinking that the latency shouldn't matter to much if you run an external card - guessing im asking you really need a crazy good latency value when running mesa boards?
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11 Jan 2017 19:55 #85622
by PCW
Replied by PCW on topic MESA stepper cards.
Normally you only run a servo thread and you cannot run a base thread with the Ethernet cards
Servo thread jitter will cause some velocity noise if more than say 100 usec latency
if this is an issue you can use a firmware config with a DPLL module and enable it
All Ethernet firmware modules have the DPLL and it can be added to PCI firmware
with the DPLL even 500 usec or so of latency is fine, as long as you can reliably service
the card at 1 KHz, all is fine.
The DPLL module reduces the sampling jitter to the ns region even with 100s of usec
of access jitter
Servo thread jitter will cause some velocity noise if more than say 100 usec latency
if this is an issue you can use a firmware config with a DPLL module and enable it
All Ethernet firmware modules have the DPLL and it can be added to PCI firmware
with the DPLL even 500 usec or so of latency is fine, as long as you can reliably service
the card at 1 KHz, all is fine.
The DPLL module reduces the sampling jitter to the ns region even with 100s of usec
of access jitter
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- Moronicsmurf
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11 Jan 2017 20:21 #85623
by Moronicsmurf
Replied by Moronicsmurf on topic MESA stepper cards.
That's interesting. I have been fiddling with getting linuxcnc working on a "Lattepanda".. and the latency is well not the best.. around 390usec. So what you are saying running steppers on this card should be fine tho or at least in the application i consider it for (Plasma table). =)
Thanks this answers as a question that comes up on a swedish forum im active on where they basicly think u need 5usec on everything or it will fail. (yeah exagerated) ;D
Thanks this answers as a question that comes up on a swedish forum im active on where they basicly think u need 5usec on everything or it will fail. (yeah exagerated) ;D
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- tommylight
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11 Jan 2017 22:21 - 11 Jan 2017 22:31 #85627
by tommylight
Replied by tommylight on topic MESA stepper cards.
I have plenty of smal machines working from laptops with latency of 300.000 directly driving L298 from parallel port, they work nicely. Although they never do the same job twice, they do pictures on granite.
Latency is not a big problem as some tend to make it, check latemcy, edit ini file to a bit more than that, check how fast you cam push the drives/motors. On slow machines that works out perfectly, but not on fast moving machines, that requires way less lag.
Easy math: base thread of 300.000 so to be safe say 500.000 makea for 2000 pulses per second if a pulse per cucle used or 1000 pulses normaly, on a full step drive that is 5 RPS or 300RPM, 1/4 miceostepping stil makes 75 RPM, still usable speed for a lot of aplications.
That is all nice and dandy, but when it comes to quality, Mesa is the way to go, and from extencive experience i can conclude: for stepper systems Mesa 7i76E with some Lam Technologies drives is the best combo money can buy.
Latency is not a big problem as some tend to make it, check latemcy, edit ini file to a bit more than that, check how fast you cam push the drives/motors. On slow machines that works out perfectly, but not on fast moving machines, that requires way less lag.
Easy math: base thread of 300.000 so to be safe say 500.000 makea for 2000 pulses per second if a pulse per cucle used or 1000 pulses normaly, on a full step drive that is 5 RPS or 300RPM, 1/4 miceostepping stil makes 75 RPM, still usable speed for a lot of aplications.
That is all nice and dandy, but when it comes to quality, Mesa is the way to go, and from extencive experience i can conclude: for stepper systems Mesa 7i76E with some Lam Technologies drives is the best combo money can buy.
Last edit: 11 Jan 2017 22:31 by tommylight.
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21 Jan 2017 03:26 #86334
by steveb48
Replied by steveb48 on topic MESA stepper cards.
Does LinuxCNC offload the step / dir generation to the mesa card? I can't find a place in the docs that says that. My system uses micro steppers which was overkill. It really taxes the computer creating the pules out of the parallel port. I'm wondering if using a mesa board would solve that. I'd replace the steppers and drivers but they are pretty nice units.
Steve
Steve
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21 Jan 2017 04:59 #86340
by rodw
Replied by rodw on topic MESA stepper cards.
My understanding is that the Mesa stepgen is told to generate steps at a given frequency until it is told to change the frequency or stop. Mine comfortably does 25x microstepping on ordinary stepper motors at up to about 650 rpm. You only run the servo thread and my latency is quite high.
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22 Jan 2017 22:52 #86441
by andypugh
Yes.
Replied by andypugh on topic MESA stepper cards.
Does LinuxCNC offload the step / dir generation to the mesa card?
Yes.
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