Rotational Axis (ABC) Limits Behaviour

DocTrucker

Morning,

Looking at something akin to a clay syringe printer. The nozzle axis will be declined from the z-axis and the orifice will always be pointing backward while printing. I will be using an additional axis to rotate the deposition nozzle in order to keep the deposition axis, and printed vector in the same plane.

Ideally there would be no limits to the rotationsl travel in either direction. What is the formal way to clear axis limts from the axis maxima and minima?

If a continuous rotation can't be achieved then the rotation in either direction will be limited to a fixed angle in each direction. If I subsequently set the machine on a vase print then at some point the head will wind up to its limit. Are the limits on rotational heads treated different to XYZ? Does the machine stop briefly rewind to a set value, and then continue? Guess there would be a good call for look ahea here to ensure it wound back the best amount?

Thanks.

Phaedrux

@DocTrucker said in Rotational Axis (ABC) Limits Behaviour:

Ideally there would be no limits to the rotationsl travel in either direction. What is the formal way to clear axis limts from the axis maxima and minima?

The most recent 3.2 firmware has rotational axis built in. They default to ABC axis. release notes will tell you more.

DocTrucker

~~No mention of ABC in the gcode guide for G1 G0? Assume they can be addressed directly?~~

~~A|B|C not available on second generation firmware?~~

"UVW available in RepRapFirmware 1.16 and later"

"UVWABC available in RepRapFirmware 1.19 and later"

"UVWABCD available in RepRapFirmware 3.0 and later"

https://duet3d.dozuki.com/Wiki/Gcode#Section_M584_Set_drive_mapping

DocTrucker

Looks like the documentation for setting up UVWABC is not at a consistent level for jerk, acceleration, dimensional limits, motor currents, microstepping.

DocTrucker

Total search hits about the ABCD rotation axis in the Changelog is:

"When new axes are created using M584, if no R parameter is specified then the default for axes ABCD is now rotational. Use the R0 parameter if you want them to be linear."

Expanding the search to rotational gives:

"M584 has a new S parameter which specifies whether new axes created in the command are to be treated as linear (S0) or rotational (S1) for the purpose of feedrate calculation. This is separate from the R parameter, which specifies whether new axes are rotational or not. The default is to treat linear axes as linear and rotational axes as rotational. You only need to provide the S parameter if you want to change the way that the feed rate is applied."

"Feed rate calculations did not confirm to the NIST standard when the Z axis and one or more rotational axes were moving, but not X or Y. This affected CNC machines with rotational axes, and OpenPnP."

https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x

I've seen mentioned in this forum that the rotational axis are not kept in sync with the linear motions?

How is a rotational and linear axis treated differently?

How do you define an axis as limitless? A belt printer would raise a similar question?

Edit: If you have a limitless rotational head, four parts with three external contours the cumulative angle could reach over 3 million with 0.2mm layers on a 200mm build. Will overrun on the data type be a likely issue?

DocTrucker

Here is the NIST standard referenced in the documentation commantary on M584

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=823374#G5.1010695

So angular feedrate is F, if only the rotational axis are moving. Not sure how to specify angular rate if a linear axis is moving. Will the move be completed in the time it takes to travel the linear distance from start to finish of the G1 command and the rotational speed set to achieve this? I assume if a rotational axis becomes a limiting factor then the whole move will be slowed rather than having a XYZUVW motion pause at the end of the G1 vector while the ABCD axis catch up?

Edit:
In other words ABCD behaves very similarly to E, including how solo moves alter the interpretation of F? So there are three stores of F values; linear feedrate, solo extrusion feedrate, and solo rotational feedrate?

Presume this line from the G0/1 doc:

"Not all parameters need to be used, but at least one of XYZEF must be used"

...should read as follows?

"Not all parameters need to be used, but at least one of XYZUVWABCDEF must be used"