defeating fillament unwinding defects by using 2 steppermotors

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ronka
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defeating fillament unwinding defects by using 2 steppermotors

Post by ronka » Tue Jul 11, 2017 6:26 pm

this is the problem: my bowden extruder is leaving thinspots in my print, i know that is the drawback of this type of extruder and after rigorous finetuning the webbing/blobbing is almost gone.(blue arrows indicating feed lagging after retract)

that left another piece of the puzzle open, the open grid that sometimes forms in the print.. (shown by the red arrows)
if you see the upper red arrow the next layer also had the grid making the print partial seetrough (this time not a desired effect :D )
after a lot of research i found the culprit to be the unwinding of the spool of fillament..
doing a test by releasing the stress of unwinding by the e-steppermotor the problem was solved..

manually unwinding is not realy doable if youre printing a few hours so my solution would be to use the steppermotor from my second extruder(wich i dont use anymore and have removed from the x carrier to make room for a cooling fan and webcam-mount ) to take the unrolling part and feeding it into the other motor thus creating a constant feed..

an option is to fysically connect the 2 motors onto 1 driver but that needs a rewire of the connector and adjusting the steppercurrent..
also making a friction free spoolreel is an option but a software solution would be a whole lot easier!! (and hey, the motor is currently doing noting anyway)

i searced the web but can't find anything for the E steppers (tons and tons of z steppers but thats NOT WHAT I'M SEARCHING GOOGLE :evil: )

now my question: how to alter marlin firmware so E1 stepper follows E0 stepper, any other thoughts would be appreciated..
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extruderproblem.jpg
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PartTimeRonin
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by PartTimeRonin » Tue Jul 11, 2017 6:33 pm

Can you show the pic of how the filament travel from spool into the extruder?
I used to use Bowden setup but didn't have that kind of problem.

ronka
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by ronka » Tue Jul 11, 2017 7:44 pm

hello PTR.

my workhorse: cheapo(ish) china prusa reprap aluminium..

blue line is the filamentroute now traveled, spoolholder rolls quite smooth on barrings, angle of feed reasonable straithtrough..
nice constant arc to hotend in any position of the carrage, no slipping or grinding of filament, or missing steps whatsoever.

red line is my proposed route, with al loop to compensate for over or underfeed from the second stepper..

(upper side upgraded display and on the lower leftside my added partcoolfan and vomit-cam that i took the photo above with 8-) )
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filament run.jpg
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chumm
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by chumm » Tue Jul 11, 2017 10:31 pm

I feel like this problem should be able to be solved another way at the spool level by adjusting the friction, but it is simple enough to run 2 motors at the same time.

I also think if you want to run 2 motors concurrently, it will be much simpler to connect them in series. Here's a good tutorial on an easy connector to make: http://www.instructables.com/id/Wiring- ... in-Series/ This will run then both identically, so if you wanted to run them at different speeds you would need to gear one up or down.

Still, if software is your preference, the most straightforward method would be to use some color mixing functions that are usually reserved for two extruder motors pushing filament at the same time. This is not possible in Marlin I think, but Repetier firmware can do it. Here's a post with some tips on how to make it work: http://forums.reprap.org/read.php?41,52 ... msg-529764

That post is referencing actual color mixing, but you could use the weight values to come up with a proportion that you want to move both motors. This would probably also involve having to change other settings to push proportionally more filament, since the firmware would believe it was getting filament from 2 sources instead of one. So if you were running both motors at 50% weight, for example, you'd need to double your extrusion to actually get one motor to extrude the full 100% amount. Overall I think this would really start to make a mess of your settings and you'd have to remember the weird tricks you had to do to make this work when trying to make any other adjustments.

The problem sounds more physical than software, so I think that's probably the most appropriate place to look to fix it.

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megamaking
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by megamaking » Wed Jul 12, 2017 4:31 pm

interesting idea. I think there are a few ways to address the issues without resolving into this... but i like the idea somehow. :D

1. adjusting the spool holder to a better position/setup so that less force is required to unwind the filament
2. increase the tension on the extruder and pump more current into the extruder?
3. extruder that is able to grip onto the filament better (bontech? e3d titan) ?
4. motorized the spool holder to unwind filament on demand (but i can see a problem, which is the turns needed to unwind N amount of filament is ultimately decided by how much filament is left (since the thickness/diameter of the winded filament reduces over usage).

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PartTimeRonin
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by PartTimeRonin » Thu Jul 13, 2017 12:45 pm

Maybe do a reverse bowden tube, run it from extruder to the front of filament spool. Add a fix point for bowden coupler.

ronka
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by ronka » Fri Jul 14, 2017 2:33 am

hi all..

i have meddled somewhat in the firmware but because marlin is kinda seriously complicated i didn't get closer to the software solution i wanted.
in ramps.h the pins used on my board are #defined so the simplest way seem to me to add the pinnumbers from e1 statements to e0 but marlin is not accepting this in the compiling stage.. maybe someone with more C++ knowledge could easily get around this but i cannot get it to function..

browsing thru the different library's i have seen shards of coding about colormixing but as chumm stated that would give hasseling mixratios and other boobytraps so i dont even bother on that route..

because im more the guy who rather works smart than hard i had hoped(against better judgement..) a software solution would be possible making hardware changes unnecessary..
so the path i now chose is the dirty one of wiring the 2 extruders to e0.. first trial is done on a breadboard as seen on the photo,
.
wiring.jpg
wiring.jpg (417.18 KiB) Viewed 1065 times
notice i didnt wire the motors in series against the advice of the link in the instructables (because i am like that 8-) )
after the alteration i boosted the Vref to get enough current for the motors.. and succes!!
.
extruders.jpg
extruders.jpg (223.24 KiB) Viewed 1065 times
both motors are working and feeding filament.. i havent come to test the setup yet in a print but that will be resolved in the upcomming days..
if all is well i'll try to tidy up the wires..
PartTimeRonin wrote:
Thu Jul 13, 2017 12:45 pm
Maybe do a reverse bowden tube, run it from extruder to the front of filament spool. Add a fix point for bowden coupler.
how should i see this, is it to get a constant loadpoint for the motor?
i can imagine it would be helpfull for eliminating the filament being pulled under various angles to the motor, thereby defeating most of the buildup of tension in the filament before suddenly unwinding to a tensionless state..
if my motorexperiment fails this is the next thing i'll try.

thanks for the input.. it helps when people are thinking along side..

in case your wondering (or not :ugeek: ) what's the big bolt doing on the side of my x-axis in the first photo..
thats my tensioning of the toothed belt for the x-axis..
i found that my printer made ridges in some corners of prints i made, afer some study it seems be the result of a slack toothed belt..
so after shortening the belt by a tooth (there was no fine-adjustment on this printer) the belt made a nice high pitched humm when played as a gitarstring.
but after a view prints the humm was gone and the rippeling effect had returned..
later found out the x-carrage smooth rods were sliding around in the printed parts of the machine so the belt was simply pulling the threaded rods together!!
what made it more difficult to find root of the problem was the inconsistance of the ripple;
when the x-carrage was pulled into the direction of the stepper the tention on the carrage was imidiate, making a nice start thus no ripple..
but the other way first the slack was taken out the long side of the belt followed by the bending of the rods..
result was the making of a double ripple very close to each other, the size of the ripple depended on the location of the carrage; getting bigger when closer to the x-stepper, getting smaller if the turn was further away from the stepper..

by tapping thread into the printed part and putting a bolt into it i now can tension the belt and make the threaded rods be parralel again..
the first runs i discovered that too much tension is visible in the prints as the tooth are pulled over the smooth bearing,
so i lowered it to a bass humm.. another improvement on the original china design!!

offtherails2010
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Re: defeating fillament unwinding defects by using 2 steppermotors

Post by offtherails2010 » Sat Dec 23, 2017 3:24 pm

i Love this !

also found an article on using 2 stepper motors with the same step inputs, been reading that it could overload the tiny driver/board so having two drivers share the load, would make the hardware last longer, theres 2 hacks, one to use in a pinch, which makes sense, and one that needs a new PCB to be made.

Image

well, i think ive read this correctly anyways, here's the link

https://hackaday.com/2016/07/06/build-a ... workhorse/

hope this is relevant to this project ;)

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