Re: This engineer claims 100 grams direct extruder. I want one March 22, 2016 08:48PM |
Registered: 13 years ago Posts: 33 |
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Koko76
Because moving the encoder further away in the chain from the source of motion makes it far harder to control. As I said in the post you quoted, modern machine tools still put the servo encoder on the motor shaft, not post gearbox, and not on the moving table. A simplified version of what will happen is that the motor will hunt back and forth through the lash present in the system to get to the commanded position. It becomes harder to damp, and the max velocity and acceleration go way down.Quote
jonnycowboy
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Koko76
Good luck Paul, I believe that you will find "closing the loop" to be more difficult than you think. Modern machine tools still keep servo encoders on the motor shaft instead of the moving table for very good reason, the same one which makes it difficult to close the loop here. Personally I think this is a dead end and I am working to make a lightweight direct solution. I think I can get pretty close to the proposed magic number.
Actually why do we care what speed the extruder motor is moving? What we really are interested in is the quantity of filament extruded (or retracted).
Thus:
Why not use a small motor such as the one linked above: similar to stratasys geared maxon motor and instead of an encoder on the motor, just use the mouse sensor to determine filament movement?
Lots of torque, easy to control, and very lightweight.
Servo systems are wonderful things, they can be very accurate and powerful when sized and above all tuned correctly. But getting them to that point is certainly more complicated than dropping in a stepper motor, especially with the power levels we are talking about. A DC servo system will be marginally cheaper but nowhere near as simple or adaptable to different builds, loading and other factors. It's not a worthless endeavor, but I fail to see exactly what problems this solves.
Re: This engineer claims 100 grams direct extruder. I want one March 22, 2016 09:55PM |
Registered: 9 years ago Posts: 1,873 |
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What this solution "solves" is the magical 100g flying hot end which will never be acheivable with a stepper based solution.
Re: This engineer claims 100 grams direct extruder. I want one March 23, 2016 04:39AM |
Registered: 9 years ago Posts: 5,232 |
Re: This engineer claims 100 grams direct extruder. I want one March 23, 2016 06:59AM |
Registered: 9 years ago Posts: 49 |
Re: This engineer claims 100 grams direct extruder. I want one March 23, 2016 08:01AM |
Registered: 9 years ago Posts: 916 |
Re: This engineer claims 100 grams direct extruder. I want one March 23, 2016 09:50AM |
Registered: 13 years ago Posts: 33 |
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JamesK
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What this solution "solves" is the magical 100g flying hot end which will never be acheivable with a stepper based solution.
Unless the stepper is at the other end of a bowden. I've never used a bowden arrangement, but it seems lots of people do - what is it about bowden that we are trying to avoid/improve on?
Re: This engineer claims 100 grams direct extruder. I want one March 23, 2016 04:35PM |
Registered: 14 years ago Posts: 268 |
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jonnycowboy
Thanks for your reply Koko.
What this solution "solves" is the magical 100g flying hot end which will never be acheivable with a stepper based solution. But yes a stepper will be easier to integrate.
Servos are not that difficult to control - a good PID and high resolution/accuracy and you're 90% of the way there. The rest is software tuning.
Re: This engineer claims 100 grams direct extruder. I want one March 24, 2016 05:43AM |
Registered: 9 years ago Posts: 49 |
Re: This engineer claims 100 grams direct extruder. I want one March 24, 2016 11:56AM |
Registered: 13 years ago Posts: 33 |
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to3dornottobe
About splitting the encoder from the motor; You can't compensate structural misses (play, backlash) with PID tuning. You need an intelligence that's capable of determining the difference between the input and the output. and store these differences to make it 'as close as possible' (stil, not ideal).. But this would require both an encoded motor and an encoded reader to determine the difference between both. (still, not ideal)
Re: This engineer claims 100 grams direct extruder. I want one March 24, 2016 12:10PM |
Registered: 14 years ago Posts: 268 |
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jonnycowboy
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to3dornottobe
About splitting the encoder from the motor; You can't compensate structural misses (play, backlash) with PID tuning. You need an intelligence that's capable of determining the difference between the input and the output. and store these differences to make it 'as close as possible' (stil, not ideal).. But this would require both an encoded motor and an encoded reader to determine the difference between both. (still, not ideal)
I understand PIDs well, I use them in my day job. For an extruder however play and backlack won't be critical however since the extruder is almost always running quasi-steady state. In the start/stop motion we don't care if there is some backlash since as soon as we start up again it will take up the backlash.
I agree for a servo motor on the movement axes it would not work so well.
Re: This engineer claims 100 grams direct extruder. I want one March 24, 2016 12:29PM |
Registered: 9 years ago Posts: 49 |
Re: This engineer claims 100 grams direct extruder. I want one March 25, 2016 05:29AM |
Registered: 9 years ago Posts: 5,232 |
Re: This engineer claims 100 grams direct extruder. I want one March 25, 2016 05:55PM |
Registered: 11 years ago Posts: 580 |
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to3dornottobe
In my opinion it's complete bullshit to add an encoder to the filament.
Re: This engineer claims 100 grams direct extruder. I want one March 26, 2016 04:43AM |
Registered: 9 years ago Posts: 49 |
Re: This engineer claims 100 grams direct extruder. I want one March 26, 2016 01:06PM |
Registered: 11 years ago Posts: 580 |
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to3dornottobe
Did you read the rest of my post? There are some viable facts in that post that are not a mere opinion.
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to3dornottobe
What do you do when the extruder simple is unable to push the filament through the hole? the closed loop compensates for that, no matter what x/y coordinate the machine is having, so it might be extruding at an XY position that really didn't need the extrusion.
Re: This engineer claims 100 grams direct extruder. I want one April 10, 2016 07:24PM |
Registered: 9 years ago Posts: 1,671 |
Re: This engineer claims 100 grams direct extruder. I want one April 11, 2016 01:44AM |
Registered: 9 years ago Posts: 72 |
Re: This engineer claims 100 grams direct extruder. I want one April 11, 2016 06:55AM |
Registered: 9 years ago Posts: 1,035 |
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toxuin
So did anyone experiment with their tiny motors? What are the results? Could you share extruder design? I happen to have some tiny motors lying around, but I suppose they're too tiny to work as any decent extruder.
One particular motor I could find a spec for is KP35FM2. Rated for 24V @ 500mA, it has holding torque of 700 g-cm (0.067 Nm). According to DC42's formula and my hobbed bolt diameter it could only do any good at 31.2A which would probably instantly evaporate it anyways. What are your motor specs, guys?..
Anonymous User
Re: This engineer claims 100 grams direct extruder. I want one April 11, 2016 12:02PM |
Anonymous User
Re: This engineer claims 100 grams direct extruder. I want one April 15, 2016 07:18AM |
Re: This engineer claims 100 grams direct extruder. I want one April 15, 2016 07:44AM |
Registered: 9 years ago Posts: 1,873 |
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MKSA
OK, I saw that the idea of using a flexible shaft like used for drill has already be done with the Flexidrive !
Definitively better than a Bowden system.
But is there a future for FDM, it is so god damn slow.
Re: This engineer claims 100 grams direct extruder. I want one April 16, 2016 03:34PM |
Registered: 8 years ago Posts: 62 |
Re: This engineer claims 100 grams direct extruder. I want one April 16, 2016 04:04PM |
Registered: 9 years ago Posts: 1,035 |
Anonymous User
Re: This engineer claims 100 grams direct extruder. I want one April 17, 2016 01:12AM |
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powdermetal
I gave the cycloidal gears a chance: Using an existing NEMA8 (4Ncm) with a 3D-printed 36:1 gearbox works quite well - extrusion rates and retracts are fine: Cyclo Extruder for a delta printer
Although being created on a well tuned and precise machine, I am probably lacking precision of the 3D-printed excenter, gears and the assembly: There is some waviness in surface appearance resulting from non-uniform extrusion - my old style bowden setup shows better quality.
Lets see, what we can do here...
Re: This engineer claims 100 grams direct extruder. I want one April 18, 2016 11:14AM |
Registered: 13 years ago Posts: 33 |
Re: This engineer claims 100 grams direct extruder. I want one April 18, 2016 04:14PM |
Registered: 8 years ago Posts: 62 |
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jonnycowboy
Powermetal, are your files available?
I'd like to rework it for the NEMA14 two-bolt stepper (50g only - 14HR08-0654S). With your solution we could bring the complete cold/hot end down to 100g combined with the new DeltaMini hot end.
Re: This engineer claims 100 grams direct extruder. I want one April 18, 2016 04:30PM |
Registered: 13 years ago Posts: 33 |
Re: This engineer claims 100 grams direct extruder. I want one April 18, 2016 05:54PM |
Admin Registered: 17 years ago Posts: 13,986 |
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powdermetal
Regarding precision: Is there anybody, who has access to a precise lasercutter or watercutter, who could cut properly toleranced gears from plastics to see, whether this concept is viable at all?
Re: This engineer claims 100 grams direct extruder. I want one April 18, 2016 06:36PM |
Registered: 10 years ago Posts: 425 |
Re: This engineer claims 100 grams direct extruder. I want one April 19, 2016 02:41AM |
Registered: 9 years ago Posts: 5,232 |
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Mutley3D
Tha above mentioned motor is 130g according to spec sheet?