crazy idea: arm-mounting the extruder... for the Diamond Hotend nozzle

I have a general question about a design change I want to explore, and wanted to get an idea or some opinions on what I might want to accomplish with my design change. a little about my Kossel XL:

200x200mm, 420mm height 700mm full height.
1515 openbeam
T20 belt system
40mm gap between arms,
290mm rod length
176 horizontal length
65mm effector
current extruder: E3D lite6
NEMA 17 400 step motors, 67oz/in torque (17HM19-1684S)
Alligator board ARM based controller. 1/32 microstepping on arms, 1/16 on extruder
1.75 mm PLA @ 226C
~550mm Bowden tube

Prints like a charm.

my goal: add the Diamond head nozzle with 3 E3D lite 6 heat sinks and add 2 additional extruders. I bought into the kickstarter campaign, and I expect to have one at some time in June. I might get around to assembling it in July, but I'm sure others would benefit if they are watching..

so, my current mount option for my extruder is a side mount, about center height, and midway between one of the arms. I do not like this option at all, but, since I need to add 2 additional extruders, I was thinking about the possible addition of the actual extruders, to the roller carriages. on each arm.


now, my questions, should anyone think this idea through with me....I do have some thoughts about mitigating some items, but I need some additional input on my idea....

so, the thought that I had, was, these motors should be powerful enough to carry an extruder on the center effector, we have seen that design before, but there have been debates about how that might impact the resonance, perhaps things affecting precision and the jerk factor, but I had a different thought. What if the extruder connection was closer to the arm that was moving up and down, reducing the movement of the Bowden tube, and hysteresis, and enabling a 3 extruder system. I plan to include into my design O-rings for the motor and the screws, to help reduce overall vibration transfer (for whatever is left in my design)

What I can't seem to figure out with math in my head thus far, is can each arm's stepper motor handle the additional weight of a stepper motor and extruder assembly added to the weight of the arm, right at the point of the carriage? never mind the actual design (I got that in my head and will be building it later tonight), now, at this point....



besides telling me i'm either crazy or brilliant, what do y'all think? these motors should be strong enough to handle the weight, right? would there be additional motor resonance that I'm not taking into consideration? do you think there would ultimately be any affect on the prints by doing this? I take the consideration that other printer designs have something already similar and work hard to eliminate that motor's impact to the prints...Im unsure what that would mean here.

I think that's quite a neat idea! One extruder on each carriage, so that they all have the same mass.

At a print show recently I saw the Wasp printer, which has its single extruder suspended a few cm above the effector using elastic cords from the 3 carriages, then a short Bowden tube between the extruder drive and the hot end. It appeared to work well.

I can see the following issues with your idea:

1. To make this work well, you will need to use lighter extruder stepper motors. The 17HM19-1684S is way more powerful than you need. I had to turn mine down to 500mA current to prevent it chewing through the filament when the nozzle is blocked (using a RepRap Mini Geared Extruder and 1.75mm filament). So it's running at 30% of its rated current, which implies that a motor with about 0.13Nm holding torque would be sufficient. If you increase the gearing a little, slightly lower torque would suffice. You should be able to find a Nema 14 motor that will suffice. There are already extruder designs around using Nema 14 motors, e.g. [reprap.org].

2. When you power the machine off, the weight of the extruder drives may cause the carriages to descend and the effector to hit the bed. So you may need a solenoid-released brake on each belt or on each idler pulley.

3. The mass of the extruder and elasticity of the belt will form a resonant system. You will probably need to damp this. Mounting the extruder drives on the carriages via rubber shock absorbers may help.

4. The mechanism you use to run the carriages up and down the extrusions will need to cope with the extra torque produced by gravity acting on the extruder motors. For example, instead of wheels running in the side slots of the extrusions, it might be better to use wheels running in the front and rear slots. Or, if you use sliders or linear bearings, use longer ones.

5. I think your 1515 extrusions will be inadequate (1515 is OK for he Mini Kossel, but I wouldn't use it on anything larger) and you will need at least 2020.

Edited 1 time(s). Last edit at 05/28/2015 04:43AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Look up vibration isolation mounts on McMaster or whatever you may have in your locality if it's not the us. Much better for the purpose than orings. I have my extruder mounted t my frame with them. I use the ones with a groove and mount them in holes counterbored from both sides.

What about the filaments that feed the extruders? They will have to flex with an extruder that never sits still. That works on a cartesian but could be really awkward for a delta.