[LinuxCNC/linuxcnc PR#462] Some more Python Interface doc cleanup

#1 – c-morley 于 2018-07-25

The description says units per mm or degrees – but isn’t it machine units (engineering units) ?

#2 – KurtJacobson 于 2018-07-26

@c-morley The joint units will be the same as machine units for a trivkins machines, and probably many others, but it is not guaranteed to be the same as machine units. I don’t fully understand it, but according to @rene-dev on IRC “non-triv machines can have different unis, like a robot. all joints are angular, but xyz abc is mm/deg”

#3 – c-morley 于 2018-07-26

@KurtJacobson: I agree that I am not up on non-triv at all and could be completely wrong but,
say for instance your machine is built completely in inches – It doesn’t seem right to say the joints will be in mm/degree. I would think it’s really joint units/degree, joint units being what ever is set in [JOINTS]. If it is actually mm then that would be the first time that I know of that linuxcnc used a specific unit internally.
But as I said this I am talking above my pay grade so could be absolutely missing something.

#4 – KurtJacobson 于 2018-07-26

@c-morley Now I understand your concern, I did not read your first comment properly! LinuxCNC does indeed use millimeter internally, and all other linear units are converted to millimeter. So, strange as it seems, the value of [JOINT]UNITS is the number of machine units that fit into one millimeter. For an inch machine the units value would be 0.03937in/mm, for a metric machine it would be 1mm/mm. For rotary axes the internal units is deg, so if you configure an axis in grad the units value would be 1.1111grad/deg etc. It took me quite some time to figure out was was going on, and that is what prompted me to try and clarify it in the docs.

#5 – c-morley 于 2018-07-31

@KurtJacobson just revisiting your comments.
I wonder if we should add your description of how to calculate joint units – I find it non-intuitive.?

#6 – KurtJacobson 于 2018-07-31

@c-morley it probably would be good to include a description of how the joint units are calculated, but I doubt anybody even used them, so it may not be worth the effort.

#7 – KurtJacobson 于 2018-07-31

Thank you @c-morley!