Sunday, July 18, 2010

Tweaking the extruder

Interesting developments this week, managed to get the extruder to extrude PLA at a consistant rate without stalling, but only through the host test extrude, still this is big step forwards.

I've also begun work on redoing the Z axis.

Before I get too far there is still one little thing that needs doing, setting the value of the extrusion rate in firmware for the motherboard, E_STEPS_PER_MM.
For the standard Mendel with a splined shaft this value is 0.706, while Adrian B. has set this to 2.0 for his geared extruder, though I found out last night that this number is wrong, its too low.
First I had read this blog post

After which I had to ask Adrian if this is equation he used, which it isn't, instead Adrian says that its

1 / (PI . Dpw / Stepper steps) x ((ratio of filament in to nozle dia or Fd / Nd)squared)

PI = 3.14159265
Dpw = 5mm
Stepper steps = 400
Fd = 3mm
Nd = 0.5mm
Comes to 0.707 which is wrong, so I fiddled the equation a bit to come to

((PI x Dpw / Stepper steps) x ((ratio of filament in to nozle dia or Fd / Nd)squared)) / 2

I get 0.706858, and the note in the firmware says its emperically adjusted, so by taking 3sf past the dp you get 0.706.

I don't know how correct this is yet, so i'll update the wiki later

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