Raspberry Pi 4 with Mesa 7c81

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06 Apr 2021 07:09 #205047 by JohnG
Replied by JohnG on topic Raspberry Pi 4 with Mesa 7c81
After looking at the .ini file again I did notice that the MAX_VELOCITY values for the x and y axis are different as follows

X
MAX_VELOCITY = 1.01666666667

Y
MAX_VELOCITY = 1.0

I don't think this could cause the problem...
The acceleration, ferror, and min_ferror are the same for all axis

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06 Apr 2021 13:58 #205112 by PCW
Replied by PCW on topic Raspberry Pi 4 with Mesa 7c81
I some was thinking mm instead of inches

Can you set ferror to .002 and min ferror to .0005
and try again?

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06 Apr 2021 16:25 #205142 by JohnG
Replied by JohnG on topic Raspberry Pi 4 with Mesa 7c81
Absolutely. Will try it shortly.

I spent a lot of time reading about ferror last night and don't completely understand how that works on an open loop system...

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06 Apr 2021 17:53 - 06 Apr 2021 17:53 #205154 by PCW
Replied by PCW on topic Raspberry Pi 4 with Mesa 7c81
Mesa (and I think Pico systems) stepgens are actually run in closed loop mode
though the loop is closed in hal. Basically the step generators run in velocity mode
and the local PID loop monitors the actual step count (and fractional step count)
and adjusts for minor deviations caused by differences in LinuCNC and the stepgens
clocks, lack of frequency setting resolution etc etc.
Last edit: 06 Apr 2021 17:53 by PCW.

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06 Apr 2021 18:14 #205160 by JohnG
Replied by JohnG on topic Raspberry Pi 4 with Mesa 7c81
It would appear that changing the ferror and min ferror values has solved the problem. I will run a few more tests to be confident. Much thanks again to PCW and andypugh! You guys are awesome!

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06 Apr 2021 18:15 #205161 by JohnG
Replied by JohnG on topic Raspberry Pi 4 with Mesa 7c81
Also thanks for that explanation of the ferror. Makes total sense now that you said it's closed in hal. That was the part I was missing!

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06 Apr 2021 18:18 - 06 Apr 2021 18:19 #205164 by PCW
Replied by PCW on topic Raspberry Pi 4 with Mesa 7c81
Changing the ferror limit will have no effect on the motion _except_
it will trigger a following error and fault if the hardware stepgen gets
out of sync with the commanded position by greater than the limits.
I suggested reducing them to guarantee that the stepgen is doing what
its told (if not it would fault and stop motion)
Last edit: 06 Apr 2021 18:19 by PCW.

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06 Apr 2021 18:45 #205170 by JohnG
Replied by JohnG on topic Raspberry Pi 4 with Mesa 7c81
After reading this I get the impression that this shouldn't have fixed it? Is this only for and error message generator or does this actually control the maximum allowable error?

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06 Apr 2021 18:52 #205172 by PCW
Replied by PCW on topic Raspberry Pi 4 with Mesa 7c81
FERROR and MIN_FERROR are only for generating faults
from following errors. Following error is the difference between
commanded position and the actual position.

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06 Apr 2021 18:55 #205173 by JohnG
Replied by JohnG on topic Raspberry Pi 4 with Mesa 7c81
Now Im even more puzzled! I will try to run some more tests later today

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