…code, cg, electronics, 3d printing…

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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:
  • 
• 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:
  • 
• 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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May as well show the good stuff first:

Even though the electronics still look like a giant pile of spaghetti out the side of the bot, there wasn’t much left stopping me from actually printing something.  But, a few things still needed addressed:

• My build-platform wasn’t remotely level, it was drooping way too much on the front.  With the help of my wife and son, I loosened up all the bolts holding the cantilevered 20×40 beams to the Z-stage, had my son slightly lift up on the end of it, and I re-tightened everything while my wife helped hold a wrench on the rear of the nuts where needed:  That got me able to level it with some z-endstop adjustments.
• Based on where the hot-end homes, there’s a 2mm X & 25mm Y offset from the corner of the build platform (calculated my manually moving the toolhead on X&Y via the LCD to the corner of the build platform).  I couldn’t figure out where in Marlin to enter these values:  Obviously the head needs to move to this position from home and ‘start’ the print there, as 0,0,0.  I slice using Simplify 3D, and I finally found these offsets in the “G-Code” section of the Process window, under “Global G-Code Offsets”.

I also needed to configure Simplify 3D to actually recognize this machine:  Luckily version 3.0 came out just yesterday, and has a new machine ‘Configuration Assistant’ that made the process of ‘building’ my machine pretty easy.

From there, I imported a simple 1cm calibration cube, slapped some blue painters tape on my build platform, and fired it off.  It’ immediately started moving, but not extruding:  Come to find out, even though I had all my stepper wiring in the Rumba the same, I had to flip the harness on the Bowden extruder 180 to get it to extrude the direction.  With that resolved, take two worked flawlessly:  A few minutes later, a tiny 1cm cube appeared:

1st print!

This was printed with a 1.0mm E3d-v6 Volcano nozzle, at 500micron layer height.  Beefy!  Surprisingly using my calipers, it was within .02mm tolerance on all axes:  Not bad for a first print!

Safe to say I’m pretty happy that it ‘just worked’ on the first try.  Now that I know it works I’m going to clean up all the wiring next, then get into the print calibration phase.

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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.

After posting my z-stage problems to the C-bot forum, they suggested I try a couple things:  Loosen up the bolts on the ACME lead-screw blocks, and switch to using dual motor drivers, rather than one, like I’m currently doing.

I loosened things up, and it helped a negligible amount, but I was still unable to predictably raise the build platform.  So, I decided to dig into Marlin and enable dual-z-steppers.

Which I did, and then added an additional A4988 driver to the Rumba board to make use of it:

A4988 Drivers, with dual-z support.

I added the additional A4988 to the “Extruder 2” plug (on the far right), plugged the right z-stepper into it, and gave it a go:  The steppers would only lower, not raise.  NOW what?

Looking at the Marlin code, I noticed that the block I enabled (starting with ‘#define Z_DUAL_STEPPER_DRIVERS’) to support this looked different from the same block in the “Marlin Configurator“:  It appeared that it was also enabling “dual z endstops”, which I didn’t want to happen.  Rearranging the code resolved this, and now I have a bed that both lowers, AND raises.  Finally.  I was going to post this code-fix, but I diff’d the Configuration_adv.h file Mason had given me with the one I pulled down from GitHub, and that code section was radically different.  I’m not sure which is newer\older.  At least mine works now…

Now that I have the z-stage working, I decided to focus on the endstops:  I had mocked them up earlier, but didn’t have them wired properly… at ALL.  I spaced out and thought I only needed two wires (+-), but in reality you should also hook up signal, so the LEDs light up.  More splicing and crimping ensued, and I got the Geeetech v1.2 endstops wired up correctly, based on this great pic Mason pointed me to…

… living in this thread, that explains it pretty plainly.  Thus the end results:

From there, it’s getting them plugged into the Rumba correctly:

Note: Since I took this pic, I’ve changed my Y endstop so it is now Y-

Here’s the logic behind it:

• Looking down on the build platform, zero XYZ is in the bottom left corner. +X is to the right, +Y is towards the back, and +Z is up.
• The X-endstop is on the left side of the Y-gantry, that the extruder blocks hits when traveling left:  It is in the “negative” position, thus X-.
• The Y-endstop is mounted on the top-left-rear corner of the printer, and the Y-gantry hits it when it moves back in a ‘positive’ direction.  So it’s Y+.
  • Note: Since I authored this page I’ve moved my Y endstop to the top-left-front corner, so it’s really Y- now.
• The Z-endstop is mounted towards the top of the left rear leg of the printer, that the Z-stage hits when it lifts up.  Since when the build platform drops it’s going in a ‘positive’ direction (or, instead, imagine the build platform on the bottom of the printer, and the nozzle lifting up instead, which is effectively the same thing), it means it starts at the negative position, thus -Z.

Note: Since I took this pic, I’ve changed my Y endstop so it is now Y-, or on the front-left of the bot, rather than rear-left as in this pic.

Once the endstops were wired up, I was able to ‘auto home’ the whole system from the LCD, and… it worked.

Finally, no more blockers… next up will be calibrating the XYZ travel distances.

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