2 Extruders, same Driver?
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Hey, just considering adding a bit of a hack for TPU. I have a gravity feed as the extruder in my M2 does not work well with TPU. Yes, I could replace it with a setup that works better for TPU with dual gears. However, I have an extra extruder setup and was thinking about mounting it under the bearing supported gravity feed spool so it pulls the filament, then some slack and into the actual extruder.. The question is how do I drive this second motor so it is in sync with the one on the printer. Can it be run from the same driver? Or is there a way to map both drivers to be E0? If this is documented please point me to it.
Thanks! -
@airscapes Push-pull extruder arrangements have been done and it's quite easy if you have a spare stepper driver. Add the driver as a second extruder in M584 using a colon separator. So for example if your existing extruder is driver 4 on the main board and you want to use driver 5 as well use M584 .....E0.4:0.5. Set the drive direction using M569 (e.g. M569 P0.5 Sn)
Note that from now on, the extruder drives will be referred to as extruder 0, and extruder 1 and not by their physical driver numbers. So you'll need to configure micro stepping (M350), steps per mm (M92), instantaneous speed change (M566, maximum speed (M203) acceleration (M201) and motor currents (M906). In all of those cases, use the colon separator and use the same numbers as for you existing extruder (e.g M350 X16 Y16 Z16 E16:16).
Next you need change your tool definition to use both extruders. It might be more convenient to create a new tool just for TPU. So for example if you have tool zero defined M563 P0 D0 H1, then either amend this to be M563 P0 D0:1 H1 or create a new tool tool M563 P1 D0:1 H1. It depends on how to want to use the push-pull arrangement. If you want to use it for everything, then stick with one tool.
The final thing you need to do is enable mixing and in this case we want to use 100% of both extruders. So use M567 Pn E1.00:1.00 (where n is either 0 or 1 depending on whether you created a new tool or altered the existing one).
You'll likely have to play around with the steps per mm so that the filament between the two extruders is neither stretched too tightly nor forms a large loop over the course of a print. In theory, the steps per mm should be identical but the first extruder might stretch the TPU as it comes off the reel or it might leave "bite" marks which the second extruder will encounter.
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@deckingman Thanks so much for the highly detailed explanations! Yes, I assumed making the loop/slack just right so the X carriage can move from end to end without the filament binding or getting caught on something may be the tricky part. Will come back to this thread once I get to this portion of the project! This really does not look as difficult as I had thought.
Thanks again!
