Add External Extruder to UM3

[Vince90 0]

Hello everybody!

just got my new UM3 couple of days ago!! For an academic project, we are trying to set up a 3D printer that can work just as a normal 3D printer but at the same time can also print different materials (i.e. very dense fluids) using an external extruder/spray. Imagine, for example, that you want to coat your 3D printed structure with a conductive layer. You could spray coat a conductive polymer onto your PLA structure.

In order to achieve this purpose, we've purchased an eco-PEN which can be controlled by an external controller. So far so good! The only problem is that since the external pen has a different controller than the UM3 when you load your STL the pen won't know its position. In other word the pen won't know whether to or not to print. This is our idea: use the signal that the UM3 sends to the second Extruder as controller for the external pen. When the UM3 board tells the second extruder to print we will turn ON our pen, while when the second extruder is off we will tell our pen to stop printing. Of course, you won't be able to use the second extrusion but you can gain a lot in the flexibility of your 3D printer.

This is what we were thinking of doing to achieve all of this:

1 - unplug the socket that connect the stepper motor of the second extruder from the UM3 controlling board.

2 - connect our detecting circuit to the same socket in order to detect when the second extruder of the UM3 is supposed to print. this circuit will basically sample the voltage across the H-bridges controlling the stepper motor and this signals will be send to our controller.

The question is: given your experience with the UM3, is this doable? I tried sampling the signal that the driver of the extrusion stepper motor sends and I can see when the motor is switched ON or OFF.

Have you heard of anyone trying to do the same?

My knoweldge about the internal circuitry of the UM3 is very limited especially because I couldn't find the schematic of the board anywhere.

Thanks for your help

Vince