Fan speed controlled by volumetric flow rate?
Would it be possible to control a part cooling fan based on the current volumetric flow rate? Basically instead of having the slicer choose a fan speed based on it's algorithm, let the Duet control it based on how much is being extruded. The way I see it, the higher the flow rate it, the larger the thermal capacity of the deposited plastic, and therefore the more cooling needed to solidify it in time.
Now I can already see times when this wouldn't be ideal, mainly times when the slicer is choosing a fan profile based on feature type rather than pure layer time, such as bridging, or overhangs, and possibly very small features. But even with small features, even though the flow is less and so the fan speed would be less, the time spent on the area is increased, and cooling is a factor of air temp and time spent.
Anyway, is this something the Duet and RRF can do predictively? Can the system know the flow rate early enough to modulate the fan PWM signal in time to sync with the area being printed. Blower fans have a lag time to get up to speed. Being able to compensate for that lag time would be ideal, and so some sort of look ahead would need to happen.
Anyway, do you think this idea has any traction, or am I just out the lunch?
It won't be easy. What do you expect to be the benefit of reducing the flow when the extrusion rate is low?
Really just came to me after fighting with cooling profiles in the slicer. I figured there has to be another way. No idea if that's a better one. Likely not.
As for the benefit, I guess I've just found layer adhesion and warping issues on small details because the print head is spending a lot of time in one area and it seems to cool off more than wanted. The slicer is only going by layer time.
In Cura you can force a fan speed at a layer height. I haven't checked yet but maybe you could use an infill mesh to modify fan speed in a section of the model.
I know the real solution is going to be in the slicer rather than firmware.