Can BBB drive real lathe?

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25 Jan 2014 01:18 - 25 Jan 2014 01:20 #43133 by eslavko
Hello...

In the future I wan't to fit linuxcnc to my minilathe (chinese 12")
Now I wonder if I can use BBB as computer? Can drive two steppers with fast step/dir?
Can manage thread cutting (the main reason to put CNC on this lathe)?

I see on video that BBB drive some repraps.. so something work but is it usable in real world?
Last edit: 25 Jan 2014 01:20 by eslavko.

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25 Jan 2014 01:51 #43135 by PCW
Replied by PCW on topic Can BBB drive real lathe?
It should be entirely possible.

Currently it may require a low resolution encoder on the spindle
to allow encoder reading in software, but this should be fixable
eventually by either a PRU encoder module or using one of the
hardware encoders built into the Sitara chip on the BBB

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26 Jan 2014 22:29 #43199 by eslavko
Replied by eslavko on topic Can BBB drive real lathe?
This type of lathe can reach 2500rpm. And as I know mostly use only one pulse as index/rpm and not some 100cpr encoders.
How fast thread PRU emulate? If I can reach result as with 15 to 20us base thread PC machine then should be nice...
And for lathe there are just two motors, two switches and spindle signal (I will keep lathe to be usable for manual working too).

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26 Jan 2014 23:24 #43206 by PCW
Replied by PCW on topic Can BBB drive real lathe?
I think the default PRU "thread" rate is 10 usec and
can likely go a fair amount faster.

I dont know if theres a encoder PRU "comp" yet.
If not, i'm sure there will be one eventually

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27 Jan 2014 02:08 #43212 by eslavko
Replied by eslavko on topic Can BBB drive real lathe?
10us is adequate..
But don't know abour encoder.
As lathe run at 2500rpm max that is aprox 42 RPS(Hz) or one pulse every 24 milisecond... So for this speed seems that even HAL encoder at servo-thread can manage to get all the pulses as at least 12 periods the pulse is high and 12 periods is low (if pulse is 50% duty)

Seems that I should setup that and test it. Need 26 hours per day to finish all.... :woohoo:

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