Rods "Spaceship" Scratch built Plasma Cutter build

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23 Sep 2017 20:55 #99361 by rodw
rodw replied the topic: Rods "Spaceship" Scratch built Plasma Cutter build

robertspark wrote: --- presume you know that the eoffset_pid was updated 8 days ago (not sure that the change was though) but it may have been a tuning / bug fix if you've been busy with life + work.


Yes, I need to catch up before going further. See my comments above as to why.
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23 Sep 2017 22:02 #99364 by robertspark
robertspark replied the topic: Rods "Spaceship" Scratch built Plasma Cutter build
Ahh.... that explains it.... (sort of)

If you update the eoffset_pid, you probably want to reset the k factor to 10000, given it's now calculating / correcting for metric conversion
// Make pid gains settings comparable for either inch or mm
// machine-unit specification. With k=10000, 1 count is scaled
// by the axis.L.eoffset-scale == kreciprocal or: 1e-4in ==.00254mm
kfactor = kfactor / (25.4 * units_per_mm);
kreciprocal = 1/((float)kfactor);
dbg_state = the_state;
is_off = !is_on; // convenience pin
the_feedback = feedback;

or comment it out..... (if you're running an imperial machine)

Is there not a flag (setting / config setting) in linuxCNC that tells the machine if it's setup as metric or imperial? given linuxcnc uses G20/G21 I presume there must be a setting somewhere, Ii.e I would have thought that the HAL file would have used this as an input to toggle the scale factor if required (25.4 or 1) to be applied.
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23 Sep 2017 22:17 #99365 by robertspark
robertspark replied the topic: Rods "Spaceship" Scratch built Plasma Cutter build
If you have the time, there is a really good explanation of PID that was done for the development of the PID algorthm library for arduino here:
brettbeauregard.com/blog/2011/04/improvi...rs-pid-introduction/

One thing I suspect that the eoffset_pid will suffer from will be jerk if the setpoint is changed during the cut.... (whilst this may be unusual it is possible if you had a PMX45XP [of like I hope to hack my PMX45] be able to control the current setting on the fly so it may allow me to lower the current at the end of the cut or in the corners where I could slow the angular velocity down and therefore have less effect of centripetal acceleration ....

This is discussed here:
brettbeauregard.com/blog/2017/06/proport...easurement-the-code/
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