I have given up on making the rumba work. I tried to add a pinda probe. Didn’t work. Tried to add a bltouch. Didn’t work. Now the rumba is not communicating with with my pc. So I have moved on to using a Rambo mini but the one drawback is that it only has one extruder capability. I would like to know if there is any way to add an extruder to the Rambo mini. Whether it be a separate board or soldering or something. I am open to anything.

I don't have one but looking at the specs you'll need:

• 2 pins for a stepper stick dir and step signals for E2 (the second expansion port may provide this, but you probably loose sd or lcd support, or use max end stop pins, you can make do with soft end stops, software based)
• 1 pin for controlling the heater cartridge and an external MOSFET board that can handle at least 50 watts. Something like a IRLB8743 would do nicely, it wouldn't even get warm.
• Change the firmware pin mapping manually, so a bit of changing values in the right places is required.
• And of course an extra stepper motor, extruder assembly etc and a x carriage that holds two hot ends (or one with a second input for filament), extra roll of filament, bowden tube if you use bowden.

You'll loose some of the x build space since you need to mount two hot ends next to each other (unless you use a single nozzle with two filament inputs). It depends how close together the nozzles are and if the x carriage covers more range than the width of the bed. When I did something similar there was about 20-25mm between the nozzles, and that's the amount you loose for a single extruder print, double that with dual extruder prints.

You'll have to decide whether you want two extruder motors on the x carriage or use two bowden tubes. The extra weight of a second stepper will reduce the speed and acceleration, slowing the printer down. Bowden removes that limitation but longer retraction and leaking will be added to the challenges list.

There's already a 3rd thermistor connector on the board so you don't need to free up a pin for that.

All in all it's probably much easier to get a Chinese RAMPS 1.4 board that has it all covered with 5 stepper sticks. You don't have to change the pin mapping manually in the firmware source code, just choose ramps with two extruders and heated bed (I think it's called EE. Ramps is more hackable (and a duet for that matter) since all pins are covered through expansion ports. The duet has the added bonus of being easier to configure without having to dive into its firmware, but it does cost a lot more.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Also really need 1 pin for stepper enable, you can leave it always on, but that wastes power and keeps the stepper energised

Good point! Probably you can tap that from any existing motor enable pin.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

I am going to try and use the p3 expansion pins so I can still have lcd and sd Sunday port