Pressure advance M572

Hello. I have a corexy running on duet 0.6 and dc42's latest firmware. I have an approx 500mm Bowden tube and am using retraction and coast in S3D to manage ooze, blobs and stringing. The discussion on this thread [forums.reprap.org] has got me interested in trying out the pressure advance feature. I have a few questions about this.
- It seems that all I need to do is add M572 D0 S0.1 in config.g to tell the printer to use this. Is there anything else I need to do?
- Does this change slicer settings in any way? I'm particularly confused because Slic3r has an option to enable pressure advance but S3D has none.
- How does one figure out the optimal parameter for S in M572
- Is there anywhere I can read up about what exactly pressure advance is doing. The actual algorithm being used would be especially interesting

That's basically correct. You can send the M572 command at any time. However, you may need to reduce the amount of retraction you use, because pressure compensation will itself cause some retraction at the end of an extruding move if the S parameter is high enough, and some hot ends (e.g. E3Dv6) tend to jam if you use excessive retraction.

To tune the S parameter I suggest you try printing top solid infill with various settings. The longer the Bowden tube, the greater the S parameter needs to be. You may also need to increase the allowed extruder jerk speed to avoid slowing down the print.

What the algorithm does is to adjust the extruder drive position by a term proportional to the extrusion speed. The assumption is that the nozzle back pressure is proportional to extrusion speed, and the springiness of the filament in the Bowden tube requires extra movement to achieve the desired pressure.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hello. I have implemented M572 D0 S0.1 and there has been an incredible improvement in the quality of prints right out of the box. I can't even begin to understand what exactly is going on. I now just get a few tiny blobs on the outer perimeter after a sharp corner. Extruder is calibrated just right. Was wondering if I can tune these blobs out by changing the S parameter of M572. In other words is there some simple intuition like "increasing S0.1 to S0.11 will reduce blobs but also reduce print speed"?

Thanks in advance.

Increasing the S parameter may reduce those blobs. Most people with Bowden extruders seem to find that a value between 0.1 and 0.2 works best. If increasing S slows the print down, you can try increasing extruder jerk (M566 E parameter).

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].