Episode 2: Cupcake155 prints with MK8 & RAMBo

The first phase of my 3D printing project was to get my machine’s motion resurrected.

The second phase, this phase, was to get it printing again; check.

Cupcake155 printing in 2015

Here’s proof that it’s working:

RAMBo Board

I picked up a RAMBo v1.1 board from RepRapElectro, after receiving a lot of very helpful general support from them over IRC.

I had to drill some new holes in Cupcake155 to mount it, that went just fine:

As I wired up, I rigged connectors to keep things generic. I made adapter cables so I have an easy road to my previous equipment.

It took me a while to work-out a suitable motor wiring. I didn’t realize that different stepper drivers produce different steps/rotation (though that seems obvious now). Anyway, I found many wiring combinations that work. Here’s what I went with in the long-run:

Wire Colour of Original MakerBot NEMA Motor
(as used with RepRap Gen3 Electronics)
MakerBot Motor Pin RAMBo board Wire colour RAMBo Stepper Pin
Orange X Red Y
Black X Green Y
Red X Yellow Y
Yellow X Blue Y

Here’s a close up of my final cable wiring, including .156 type connector


I conquered the mechanical installation of the Geeetech MK8 in Episode 1.

Now for hook-up. I tried various wiring combinations, and found that the MK8 stepper could just be one-to-one connected to the RAMBo board.

As the image to the right illustrates, here’s the motor wiring for Geeetech MK8 to RAMBo:

RAMBo Pin Geeetech MK8
Extruder Pin
Red Black
Green Green
Yellow Red
Blue Blue

Beyond the stepper was the thermister and the heater wire, these are near impossible to screw up, so.. Moving on..


Firmware: Marlin

As Marlin served me well in Episode 1, with my RepRap Gen3 motherboard, I figured it was only right to keep using it. Especially when considering that the RAMBo came with Marlin 1.0.0 preloaded, and I’ve made a tiny source code contribution to Marlin now too. 🙂

Configuring Marlin for my machine took me considerable effort, loads of careful empirical measurements with my calliper and an iterative approach (I often follow a TCP-inspired algorithm when searching for something optimal).

Here’s some key highlights:


#define TEMP_SENSOR_0 5

#define HEATER_0_MAXTEMP 260

#define  DEFAULT_Kp 13.24
#define  DEFAULT_Ki 0.46
#define  DEFAULT_Kd 95.97

#define X_MAX_POS 105
#define X_MIN_POS -15
#define Y_MAX_POS 90
#define Y_MIN_POS 0
#define Z_MAX_POS 120
#define Z_MIN_POS 0

//Cupcake155 (Rambo)
#define DEFAULT_AXIS_STEPS_PER_UNIT   {93.727842795, 93.727842795, 2548.8, 101.0869}  // default steps per unit for Cupcake155 (on RAMBo)
#define DEFAULT_MAX_FEEDRATE          {5000, 5000, 150, 5000/60}    // (mm/sec)    
#define DEFAULT_MAX_ACCELERATION      {900,900,10,10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot.

I’ve posted my Marlin configuration on github, here.



I’ll be tuning this machine for a while still I’m sure, but it would seem my first 5 days with it in operation have been fruitful.

I started to produce much improved prints once I discovered the gcode, M206 Z-1.0, to manually adjust my Z=0 position (as my Z-end stop fires too early). Also I was screwed a few times by snapping PLA lines during prints, which required a little re-thinking of my spool supporting method.

I’ll add that I ran in to trouble that I’m attributing largely to chasing perfection with my Z=0 location while having a non-level print-bed. My print bed is fairly level on its own, but that means there’s about a 0.2mm variance and well, that’s enough for me to feel, severely (as in-failed prints that could have hurt the printer)

Above is part of a model of the SpaceX Dragon Capsule. Epic. Just epic.


As text-objects, I’ve been printing lots of Z-stage C-clamps for my machine. I have far too many as it is, and will find other Cupcake parts to print when I have further testing/calibration to do.

Interestingly, I’ve only ever used my pliers to hold on to the nuts of these little M3 screws as I’ve worked on this machine. It dawned on me; hey I have a 3D printer now!..


Suffice to say, that little guy works great! 🙂

Oh… And here’s a link to my Photo Album for this episode.

The adventure continues in Episode 3.