Author Topic: Best filament motion sensor? Design or buy?  (Read 5328 times)

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Offline mushroom

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Re: Best filament motion sensor? Design or buy?
« Reply #25 on: July 05, 2022, 12:54:58 pm »
There's hundreds of such designs on Thingiverse and other repos, some being 10 yo or so, some embeding over-engnineered electronics ; and many threads on RepRap forums. All are failed designs.
Filament springiness varies ; with "rigid" filaments, it's low at the begining, then becomes much higher in the end, due to the curvature radius and the way the filament is rolled up (outer vs inner filament). The filament is not a cylinder : it's a toroid with a variable diameter of revolution, and it makes a huge difference. Think of the filament as a spiral torsion spring you unroll : center is way stiffer. They are not constant springs, so there's no way to adjust the sensor.
It also depends on the material : TPU PETG nylon etc.
 

Online thm_w

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Re: Best filament motion sensor? Design or buy?
« Reply #26 on: July 05, 2022, 10:42:46 pm »
I know, 6 months...

The answer :

https://www.youtube.com/watch?v=cX-9fWV7gJY

https://github.com/yet-another-average-joe/The_Smart_Spool_Holder

Designed this a few years ago, still using it. Saved a print yesterday.
Not for all machines, but easy to redesign if needed.
Will not detect a clogged hotend, but will never fail in other situations (it just can't) : tangles, end of spool, broken filament.
Costs nearly nothing. No sensors that never work. Mechanical problem solved with a mechanical answer = simple design (didn't find how to make this work with one switch only, keeping the design simple).
If Marlin is properly configured, the print cannot fail : M600 -> replace filament and resume.

Good idea and video.
Simplicity of two microswitches  :-+

I wonder if its possible to do just the swinging outlet arm portion, with a switch on either side of it. But I suspect that would be less reliable than your method.
« Last Edit: July 05, 2022, 10:46:18 pm by thm_w »
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Offline mushroom

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Re: Best filament motion sensor? Design or buy?
« Reply #27 on: July 05, 2022, 10:48:39 pm »
I'm sorry, I don't see what you mean. Could you post some drawing ?
 

Offline Mechatrommer

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Re: Best filament motion sensor? Design or buy?
« Reply #28 on: July 06, 2022, 02:53:03 am »
tension problem is easy... just use PTFE tubing as a pathway of the filament... filament spool -> jam/broken sensor -> ptfe tubing (braced to something and to print head) -> printhead. please keep in mind printhead where the filament is inserted to is swinging around, so the curly filament will be swinging around too. you need engineering thought to deal with it. think of bicycle rear brake or car throttle cable.. thats how its properly done.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline mushroom

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Re: Best filament motion sensor? Design or buy?
« Reply #29 on: July 06, 2022, 12:32:08 pm »
You mean using some sensor that measures the filament length that goes througth the device after straightening it between two pieces of tubing ? And compare this measured length against the length calculated with the extruder steps ? The BTT Smart Filament Sensor works this way. It is a very old design (mouse wheels, etc.). Recommended settings (from BTT's user manual): FILAMENT_RUNOUT_DISTANCE_MM 7 ; 7mm is 16.84 mm3 for a 1.75mm filament ; or a 0.4 x 0.2 x 210.5mm printed line. In case of a tabgle or jam, the head moves 210.5mm printing thin air until it stops. Failed print. It's a scam.
If it is just a microswitch or some optical sensor, it can detect broken filaments, and end of filament if the end is not hooked to the spool. (last one on RepRap Forums 2022-06-28 : https://reprap.org/forum/read.php?424,889788 )
« Last Edit: July 06, 2022, 12:36:07 pm by mushroom »
 

Offline Mechatrommer

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Re: Best filament motion sensor? Design or buy?
« Reply #30 on: July 06, 2022, 01:19:39 pm »
You mean using some sensor that measures the filament length that goes througth the device after straightening it between two pieces of tubing ?
one piece of tube is enough..

The BTT Smart Filament Sensor works this way. It is a very old design (mouse wheels, etc.). Recommended settings (from BTT's user manual): FILAMENT_RUNOUT_DISTANCE_MM 7 ; 7mm is 16.84 mm3 for a 1.75mm filament ; or a 0.4 x 0.2 x 210.5mm printed line.
looking for BTT sensor keyword, yes thats what i'm talking about. now i dont have to reinvent the wheel.. it should work, if it isnt, i believe it can be fixed. ymmv.


Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline mushroom

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Re: Best filament motion sensor? Design or buy?
« Reply #31 on: July 06, 2022, 04:31:52 pm »
It "should" but it doesn't. This thing detects failed prints. Not prints that are about to fail. Except if you cut the filament.

It is a *VERY OLD* design, the Internet is full of variations around this idea. They just payed some youtubers, created the hype, and make money. The filament sensor is probably the very first accessory a beginner will add to his brand new printer. We all did it.

An example from 2016 (6 years old, just one among many others) : https://hackaday.com/2016/12/08/this-old-mouse-keeps-track-of-filament-usage/

Remember that the OP was asking about spool tangle detection. Not about detecting a filament that someone had the brilliant idea to cut using pliers. A solution that can save he's print. Not some gadget that phushes a button saying "you're f*cked").

Again, do the math. The head will move 210mm (1.75 filament 0.4mm line width, 0.2mm layer) until it reacts, according to BTT recommendations (triggers after 7mm). Too late. It is a failed print. Wasted money, wasted plastic, wasted time.

[EDIT] DOES MARLIN TAKES THIS DISTANCE INTO ACCOUNT BEFORE IT RESUMES ? I doubt it can do it as it would require to rewind the gcodes...

Have a look to the 3D printers these youtubers have all around, watching their next videos. Do you see this device on their machines ? No. Why ? Because it is useless. They took the money and throwed this crap away. Otherwise all their machines would be equiped. Some are 3D printing for a living. And you will never see these sensors demonstrated in real world situation. Just the cutting pliers trick.

I'd love to hear Thunderf00t talk about this device. I doubt he's interested in such obvious debunking.

The only real well engineered device would be something that compares the length that enters the extruder against what goes out, and is fully integrated. Extruding and retracting. Maybe it exist in the industry world...

Look at this video. I'm sure the author is trying not to laught while mounting the sensor the BTT way :

« Last Edit: July 06, 2022, 04:47:58 pm by mushroom »
 

Offline JohnG

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Re: Best filament motion sensor? Design or buy?
« Reply #32 on: July 06, 2022, 07:16:51 pm »
Quote from: mushroom

The answer :

[url=https://www.youtube.com/watch?v=cX-9fWV7gJY
[/url]

https://github.com/yet-another-average-joe/The_Smart_Spool_Holder


THANK YOU!
"Those who learn the lessons of history are doomed to know when they are repeating the mistakes of the past." Putt's Law of History
 

Online thm_w

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Re: Best filament motion sensor? Design or buy?
« Reply #33 on: July 06, 2022, 10:23:56 pm »
I'm sorry, I don't see what you mean. Could you post some drawing ?

Here is what I'm going to try:




Swinging arm will need to be tensioned down lightly with a spring or heavily weighted, when filament runs out it drops. This is the same as your design.
Normally the tension on the spool is very low, and freely turns. So if any resistance is encountered it should bump the arm up, and activate the adjustable upper switch.


Since the spool size changes, the upper switch may not work reliably, and be falsely triggered easily.
But worst case I get a working runout sensor, which I don't have yet.
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Offline mushroom

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Re: Best filament motion sensor? Design or buy?
« Reply #34 on: July 06, 2022, 10:59:24 pm »
So I understood what you were meaning !
It wouldn't work on mine because it's a bed slinger.
Yours is a CoreXY, isn't it ?
Definitely worth testing on a CoreXY (or similar).

Maybe you could make the design even simpler using one switch and a cam.



On mine, when moving up (Z axis), the arm is also moving up (I had to find the sweet spot for its axis and the max angle as it influences the force that pulls the rocker arm). The arm is also moving up and down when the filament is near the end : it unrolls like an helix.

 
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Online thm_w

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Re: Best filament motion sensor? Design or buy?
« Reply #35 on: July 07, 2022, 01:34:30 am »
Ah totally missed that the arm on yours was moving, as mine is corexy yeah.
I think if you had a really long PTFE tube going to the top, anchored to one spot, then it might have the same action. But at that point you'd have to build too much additional structure.

Good single switch design idea.
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Offline mushroom

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Re: Best filament motion sensor? Design or buy?
« Reply #36 on: July 07, 2022, 12:14:50 pm »
Yes, it's a Tevo Tornado (Creality CR10 clone), never converted to direct drive (parts are in the drawers, but always something to print...). In a near future, I plan to build a Voron or similar fast printer (tired with 30-50 mm/s and low jerk/accel). I will test your design.
Please test it with the very last meters of filament on a spool. This is where the problems occur, the filament going all over the place due to its small curvature and high springiness. (I had to tighten the nylock nut, adding friction, because the reel is pulled hard and triggers false tangle alerts). The arm moves up and down a lot, too.
 
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