On 4/20/2012 6:29 PM, Scott Hasse wrote: > Unfortunately, this approach doesn't work well for things like plastic > extrusion where it can be difficult to control the extrusion rate precisely. > Repraps, etc are able to succeed in part because they take a very naive > approach to trajectory planning and can get away with it because of the low > moving mass. They basically try to fly around at a consistent speed > regardless, and extrude at a constant rate. Yes they have to maintain speed, because any speed change would create over/underdeposition because of the nozzle time constant/overpressure. But also it should be remarked, that Marlin uses up to 32 lines lookahead for which it processes acceleration curves in advance. There is a velocity magnitude, any change of the speed vector less than this velocity will be done without acceleration. Any breaking and accelerating is done so that one reaches this "jerk" velocity change is reached at corners. From what I understand, EMC would be much slower following a typical 3d-printing gcode than marlin, due to the 1-line lookahead. What however would be nice is blending, and arc step generation, to run through with even more constant velocity.
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