Posts Tagged ‘ extruder

Building the C-Bot 3D printer: Part 21 : Software Day 4: PID Autotune & start/end G-Code

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Total time : 2.5 hours

Even though I need to really un-spaghetti the machine and do the final wiring, I can’t help but want to print more, especially since I installed & tuned the DRV8825 stepper drivers:  I want to make sure they actually work!

Start & End G-Code

At the same time, I wanted to create better start & end G-Code for the bot:  I slice & print using Simplify 3D (S3D):  When you create a new custom printer profile, for the start G-Code, all it does is a G28:  Auto-home.  It seems to take care of the extruder and bed heating for you.

In addition, even though I’d previously figured out how in S3D you can set ‘global G-Code offsets’ in its G-Code tab, which lets you define the offset between home and the build platform, I thought it’d be better to set it in the start G-Code instead. I don’t know why, but it feels safer in there…

I’ve never done any start\end G-Code ‘programming’ before. The start/end G-Code for my Replicator1 was already setup.  So heading off to the ‘G-Code in Marlin‘ page, I researched what I wanted it to do on start:

  • Lower the bed a bit just in-case it hadn’t before
  • Home all axes
  • Warm up the extruder (and eventually heated bed)
  • Purge the nozzle
  • Move nozzle to edge of the bed and zero it (per the above paragraph).
  • Start print

And on end:

  • Turn off extruder and bed heating
  • Lower the z-platform slightly
  • Home XY
  • Disable motors

Another great resource is S3D itself:  Once you’ve connected to your machine, and are in the Machine Control Panel, any commands you issue show up in the Communication log:  So I set about doing each step manually, then creating the G-Code script for them.

What I came up with is currently below.  I’m sure this will change in the future.  But just in case my computer explodes I’ll have a backup here.  Note that [stuff in brackets] is S3D’s own internal syntax for embedding variables to help make the gcode more temperature agnostic.  Pretty nice.

Start G-Code:

G92 Z0 ; Set current z position to zero.
G1 Z20 ; Lower Z to be safe 20mm.
G28 ; Safe Homing of All Axes
M104 [extruder0_temperature] T0 ; Set extruder targe temp
M109 S[extruder0_temperature] T0 ; Wait for extruder current temp to reach target temp.
G1 E50.0 F600 ; Purge nozzle 50mm at 10mm/sec
G92 E0 ; zero extruder
G1 X2 Y26 ; Move nozzle to left front corner of build platform.
G92 X0 Y0 ; Zero X & Y here to start the build.

End G-Code:

M104 S0 ; turn off extruder
M140 S0 ; turn off bed
G92 Z0 ; Set current z position to zero.
G1 Z10 ; Lower Z to be safe 10mm.
G28 X0 Y0 ; Home XY
M84 ; disable motors

So I fired off my first print over USB, and ran into all sorts of weird problems over the next hour.  Long story short:

Gotchas:

  • Every time I change a setting in S3D and want to re-print, I need to turn my printer off and on.  I don’t know if this is a S3D bug, a Rumba bug, a Marlin bug, or what.  But if I don’t do this, the start G-Code won’t properly execute.  Side effects include it not heating and immediately starting a print, or heating up but then never beginning the print after it.
  • Once that was resolved, for the longest time I couldn’t get the filament to stick to the bed:  it would just curl up around the extruder.  I finally realized that a new profile I’d setup had my layer height set to 200 micron… printing with a 1mm wide Volcano nozzle:  Once I set that back to 500 micron the printing had no problems.
  • I really need to get a print-cooler fan installed:  I built a custom one for my Replicator 1 which has really helped.  When I finally got my printing working, and was working on a 2cm test cube, the sides looked pretty good for effectively my second print:
    • not too bad
  • But when it got to the top, the whole print was so hot that the extruded top layer filaments literally started grabbing & collapsing the side-walls.  Plus when I went to remove it when the print was done, it was soft like warm gummy bear:
    • aaaugh
  • Top priority: Get print cooler fan installed.  Or maybe a jet of liquid nitrogen…. :)

PID Autotune:


Update:  Since authoring this post I have switched my electronics to RADDS, and my firmware to Repetier.  See the “Part 31 post” for the latest on it.


 

While my extruder has been heating up fine, I noticed that as it approaches the target temp (say, 200c) it really slows down for the last few degrees, and takes a long time getting to the final temp.  I remember that when I switched my Replicator 2x to Sailfish firmware, the extruders stopped heating up correctly, and talking on the forums they told me I needed to update my PID settings.

PID stands for “proportional-integral-derivative“, something I did not learn about in math class.  But in a nutshell it’s a way via the maths to reach a target value smoothly and quickly, without banging/oscillating all over the place.  And luckily, Marlin comes with a PID autotune feature you can run as G-Code directly from S3D (or any software that can issue G-Code):

M303 E0 S200 C8

Fire that off when you extruder is cold, and a few minutes later it’ll spit out something that looks like this:

Recv:  bias: 213 d: 41 min: 199.38 max: 200.71
Recv:  Ku: 77.96 Tu: 13.40
Recv:  Classic PID
Recv:  Kp: 46.77
Recv:  Ki: 6.98
Recv:  Kd: 78.32
Recv: PID Autotune finished! Put the last Kp, Ki and Kd constants from above into Configuration.h

And those values you then enter back into Marlin’s Configuration.h file.

These were my original values when I authored this blog post:

#define DEFAULT_Kp 46.15
#define DEFAULT_Ki 5.10
#define DEFAULT_Kd 104.32

UPDATE (2016-01-13) :  But I found when my powerful 24cmf cooling fan would kick on to cool the Volcano nozzle, the temp would drop, and it would take a loooong time trying to catch back up.  So instead, I cranked my fan to 100% (255) and re-running the auto-pid gave me the values in the code snatch two paragraphs up.

I never timed the nozzle warmup before, my E3d-V6 Volcano now heats up from cold to 200c in 2min 10 seconds:  Not too bad.

I’ve still not got my heated bed soldered up yet (waiting on 10-gauge wire in the mail), but I’ll run this again on the bed when it’s ready.


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Building the C-Bot 3D printer: Part 2 : Extruder Assembly

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I chose a E3D-v6 Volcano as my printer head of choice:   Since the volume of my new printer will be so big, I need a nozzle that can keep up.  I’ve never used any of their products before, but have read many good things.  Purchased a ’12v, 1,75mm, Eruption – Full Hotend (Bowden)’ kit from Filastruder.  I should note they included surplus mounting hardware (washers, bolts, crimp-tubes, etc).  While I didn’t need them, I always appreciate the extras (including gummy-bears).

It happened to be one of the first things to show up, so that’s why it get’s blogged about first 😉

Links:

Notes on the build process:

The E3d-v6 Assembly Guide is well written:  I really only got hung up on the thermistor wiring:  When cutting and installing the ‘glass-fiber sleeving’, the ends constantly fray:  I found it quite difficult to get the thermistor + it’s sleeving shoved into the small hole on the heat-block successfully with the frayed ends: I had to enlist a sewing needle from my wife to aid shoving the ends in.  Later, installing the ferrule’s (crimp-tubing) proved even more difficult, since they wouldn’t want to slide over the frayed sleeving.  I persevered, but it was a huge time suck involving very tiny things my fingers didn’t like to grip.

The only other (very minor) issue was that the screws used to hold the cooling fan in were slightly too long: They’re sticking out a couple extra mm, I just couldn’t get them screwed in the whole way without stripping their heads.  If I get really OCD I may cut a bit off the end with my Dremel.

Overall, it took me around 2 hours, but I was really taking my time, and constantly getting up to get tools since I did it in my living room instead of my workshop, and was babysitting multiple prints going on my Rep1…

The final result:

e3d-v6_volcano  Beautiful!

Must remember to do the “Final Tightening” stage before my first print.


 

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