I've been playing with the Extruder Advance feature (EXTRUDER_ADVANCE_K parameter) in Marlin, trying to reduce over-extrusion at the corners. As far as I can tell, no one, including myself, has been able to use this feature successfully. Mostly, people just crank up the jerk and acceleration to reduce the deceleration at corners, but jerking your machine around seems like a rude way to deal with what is really a synchronization problem.
What I want to do is simply advance the extruder motion profile in time relative to the X-Y motion profile by some number of milliseconds to account for the time lag between when you move the extruder motor and when the nozzle actually responds. It seems like this would be a pretty easy approximation to dealing with the hysteresis. In other words, you'd use the same extruder motion profile and X-Y motion profile normally used, but you'd just start the extruder motion profile a few millisec. before starting the X-Y motion profile.
Theoretically, this could be done by post-processing the G-code file, but you'd have to duplicate all of the path planning that goes on inside the firmware. Conceptually, is seems like it ought to be an easy thing to stick into the firmware, but looking thought the Marlin source code makes my head swim. I have no idea of whether this would be an easy thing or not within the Marlin architecture. Are there any firmware wizards out there who can tell me if this would be a hard thing to do or not, and if it is feasible, where to even start? Many thanks.
