Help Please! - Replacing Extruder Motor With Non-Captive Version  

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

💡 the stepper drivers at our i3 MK2(s) control the current of the steppers. the prusa (without multi-material kit) will drive the extruder stepper with 450mA in "silent" and 500mA in "high-power" mode.
so the voltage rating is not really important. more important is the phase resistance. because the stepper drivers at the rambo use the +12V Vcc (provided by the psu) to feed the steppers, the resistance must be low enough that the high current could be provided.... so any 2-phase stepper (with 1.8° fullstep) below approx. 22 Ohm resistance will do the job. so from the electrical point of view, your linked device should work safely.

❓ but to be honest, i didn't get the point why you would use non-captive steppers for the extruder motor, which - in my mind - requires a captive axis.
these "non-captive" motors are designed for a z-axis, where the z-motors are moving up- and downwards with the x-carriage, while the spindles are fixed.

➡ just for information: in case of the multi-material kit, the currents range from 350mA to 700mA.

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

Hi Jeff,

Thanks for the help! Does that mean that if I buy a motor with anything above an 700mA rating that it will be ok if I also wanted to use it later as part of the multi-material print? What equation are you using to obtain the 22 Ohm resistance figure?

If you look at my attached image it will explain better what I am trying to do. By using the non-captive motor and lead screw I will use it as a piston otherwise to achieve the same wit ha captive motor I would require e.g. a worm drive and it would get large/heavy so by using a non-captive I'm avoiding this (I think).

Cheers,
Alex

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

... What equation are you using to obtain the 22 Ohm resistance figure?...
12 V / 0.5 A = 24 Ohm. it's sometimes called the ohm's law....

12V because that's the maximum voltage the stepper driver could provide.
0.5A because we're talking here about the i3 MK2 without the multi material upgrade kit.

next lower standard value will be 22 Ohm.... so you got about 2 Ohm "reserve" for the cables & connectors.

anyhow, even so that you've posted your picture: i didn't get the point what you're planning to do.
with the piston and the extruder needle it seems to be a device to produce your own filament.

but in my mind this requires a completely different approach, because you need to deal with the different densities of the stuff you like to print and you need a control loop to get a consistent diameter (the diameter is not only determined by the needle, velocity and viscosity plays a role as well).

furthermore i guess that you require much more power for extruding filament from raw material than simply "forwarding" filament into the hotend (even so it's "only" alginate, agar-agar and other viscious material).

and last, but not least, without a worm gear you need to reload your piston regulary which will interrupt the steady flow required for printing.

by the way, i've came across a filament extruding device a few weeks ago (filafab), but it costs above 600$US.

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

Ah of course, Ohm's law. My old school nemesis.

anyhow, even so that you've posted your picture: i didn't get the point what you're planning to do.
with the piston and the extruder needle it seems to be a device to produce your own filament.
Not at all, I'm simple 3D printing using a different material and a syringe/needle instead of the hotend/nozzle approach.

because you need to deal with the different densities of the stuff you like to print and you need a control loop to get a consistent diameter (the diameter is not only determined by the needle, velocity and viscosity plays a role as well)
It's my PhD project so yeah there will be quite a lot of work and yes I know all of the above needs to be considered 🙂 Lot's of refining methods to come...

furthermore i guess that you require much more power for extruding filament from raw material than simply "forwarding" filament into the hotend (even so it's "only" alginate, agar-agar and other viscious material).
The power is something I'm just hoping and praying works out to be honest... The current motor I am looking at has 28Ncm which I'll be using to drive a 20/60ml syringe of the material.

and last, but not least, without a worm gear you need to reload your piston regulary which will interrupt the steady flow required for printing.
The design is such that one print = one syringe so the refilling of the syringe won't be a problem although I am curious how a worm gear would be used in your mind to avoid this?

by the way, i've came across a filament extruding device a few weeks ago (filafab), but it costs above 600$US.
I've seen a few around too yeah but unfortunately name of the game is cost efficiency. A large amount of my work is based around economics, so buying an extruder for the same price as the printer wouldn't work out

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

Been reading this thread with interest...

Only thing I can see that you would need is a physical coupling between threaded rod and the syringe plunger so that you could "retract" - suck during moves. Obviously, this is something that could be easily printed, along with the replacement "extruder" parts (including a probe holder).

Peter

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

Update: The motor works very nicely, requires an extruder multiple of about x100 on filament settings in order to work at a reasonable rate for printing but very excited to put together the syringe holder now to mount it etc.

Only thing I can see that you would need is a physical coupling between threaded rod and the syringe plunger so that you could "retract" - suck during moves. Obviously, this is something that could be easily printed, along with the replacement "extruder" parts (including a probe holder).

Hi Peter,

Yeah I thought of that, it will probably be some sort of printed mechanism that will be glued onto the back of an ordinary syringe piston part which I'll have trimmed down, leaving just the rubber parts.

Also extruder parts with probe holder currently being designed 🙂

Cheers,
Alex

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

Also extruder parts with probe holder currently being designed 🙂

Please post your results to this thread. This is very interesting, and I would like to see your progress.

--ajs

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

...
Also extruder parts with probe holder currently being designed 🙂
...

any further intermediate results or news ?
just curious

Re: Help Please! - Replacing Extruder Motor With Non-Captive Version

Hi all!

I haven't forgotten about the interest on this thread at all and will be uploading files and details on how this goes when progress is made!

Currently I have successfully installed the non-captive motor and designed the parts in tinkercad to mount it and the syringe to! This is in fashion with the original prusa i3's bolts and screws setup to hold everything toether - annoyingly my order for these bits has been delayed by 6 weeks 👿

Within the coming weeks I should hopefully be able to do real testing of my design and report back to you guys with pics/vids and share the CAD files if you were interested!.

Best wishes,
Alex