assist bowden with second small stepper

Has anyone tried using a second small stepper, like a NEMA 8 or 11, just above the hot end to help with hysterisis and retraction?

the idea has been in my head for years., but i've never had a reason to go bowden so never investigated it. the introduction of elastic filament makes me think that others might be interested.

I'm assuming you'd need another stepper driver since the specs of the two motors will be so different. another option would be to use two equal but smaller steppers; you wouldn't have as much force but the combined force might be equal to a single NEMA17 while having better retraction/hysterisis control and would only require a single driver (albeit with the loss of torque that comes from that).

Cheers

It would seem you're potentially addressing one issue by signifiantly increasing the complexity of the system requiring additional electronics and synchronizing the two different types of motors, and in the process defeating the purpose of the bowden tube setup.

I'm doing no such thing. It's only an idea, after all.

And it is increasing complexity, from my way of printing at least. I've been printing on blue tape on an unheated bed, on a Sells Mendel derivative with only a single z motor. Most everything since 2011 is added complexity to me.

The question is whether it may produce better results for boden extruders, and whether the complexity is worthwhile. Furthermore, the question is whether anyone has tried it experimentally.

I had the same idea, but haven't got round to trying it. Seems like a worthwhile idea on paper. It's quite simple, and I don't see an issue with synchronization.

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I would just do 2x Nema 17 just like with the Z-axis. You can hook up two stepper motors to one driver and have them push and pull the filament working together. In my fantasy it would be that you replace the idler with the 2nd stepper motor, so instead of the filament having a filament driver on one side and a bearing on the other side, the filament is sandwiched inbetween two stepper motors that both spin the filament in the same direction.

The only advantage I see in this way of driving the filament, would be that the teeth gripping in the filament are on both sides, thus almost encapsulating the filament instead of grinding it just on one side. This will not be ideal with gears that are made with M3/M4/M5 threadmakers because it will cause the filament to twist continuously even more than when using only one.

I dont think it will help that much, Why add dual motors when you can just use one and dual hobbed bolts?
one nema motor is certainly strong enough

Quote
nechaus
I dont think it will help that much, Why add dual motors when you can just use one and dual hobbed bolts?
one nema motor is certainly strong enough

Ofcourse, one is strong enough, but why stick with the original idea? I like it when others wonder and develop new techniques And to me it seems that 2x NEMA17 would work better because like I explained, they can pull together and minimize wear & tear because the contact surface can be made much bigger.

When you use two hobbed bolts you get more mechanical friction, and thats not what happens when you add a 2nd NEMA17

That's not really the scope of this thread. The idea here is a large motor off the x carriage and a small motor on the x carriage. many designs can't fit one nema 17 on the carriage, let alone two(whether it be size and/or weight constraints). Those printers use a bowden-style extruder, which can have oozing issues and can't print certain materials, such as filaflex.

Oh yes, you're right, I was thinking Bowden... Talking about tunnel-vision

However, I've seen plenty of X-carriages sport a double-extruder without bowden on one X-carriage. However, it looks crappy.

Wow man... A few people missing the point here!

I had this exact idea the other day... I do have a bowden setup (RepRapPro Mendel) and it is great for large objects where quick moves are permissable but on smaller, finer objects it can be hard to fine-tune 'blobbiness'...

To combat this AND keep the weight of the X Carriage light, I was thinking if I have a NEMA 14 (the RRP stock extruder motor) on the extruder (mounted on the frame of the machine) it can be heavy because it's not moving AND it is strong enough to pull and feed filament.

There is hysterisis and in the stock setup it cannot be addressed. Because of compression over the length of filament in the bowden tube (around 500mm in my case, often longer) filaments such as filaflex are not able to be used.

Installing a very small stepper COULD possibly address the problem, while keeping the weight to a minimum (size of the stepper would be as small as possible while still having enough torque to "hold" and relieve the pressure from hysterisis and compression.) The only real issue I could see would be mechanically getting the filament drives synced. It's dead simple to synchronise stepper motors, but if the hobbed bolts (assuming these are used in this setup) are slightly different there could be potential problems. Perhaps this could be addressed by using a smooth shaft for the second motor to allow it to slip slightly? Or precision machined parts may do the trick? Bowden works on its own, it's a proven concept, that said, it can always be improved!!

I like the concept of a 'slave' stepper on the x carriage. I probably won't do anything about it, but I'd be interested to see someone elses results if someone else tries it! :-)

I'd be happy to help design and produce some precision rollers / feeders as a test if someone designs and tests something. (Have access to CNC machinery at the moment)

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Quote
Ohmarinus
I would just do 2x Nema 17 just like with the Z-axis. You can hook up two stepper motors to one driver and have them push and pull the filament working together. In my fantasy it would be that you replace the idler with the 2nd stepper motor, so instead of the filament having a filament driver on one side and a bearing on the other side, the filament is sandwiched inbetween two stepper motors that both spin the filament in the same direction.

The only advantage I see in this way of driving the filament, would be that the teeth gripping in the filament are on both sides, thus almost encapsulating the filament instead of grinding it just on one side. This will not be ideal with gears that are made with M3/M4/M5 threadmakers because it will cause the filament to twist continuously even more than when using only one.

Something like this?:



It worked better than the single drive extruder, but my hot-end still managed to jam, though less frequently.

You're all nuts... lol :-P

Coming from a bowden setup, seeing a (for want of a better word) monstrosity like that! That seems overkill!?!?

Surely you cannot print at a high enough speed with such a heavy x carriage that you NEED that much torque on your filament?




Regardless, THAT is kind of the design I was talking about, except with 400-500mm of bowden tube separating the steppers ;-)

And it's NOT really what Ohmarinus was saying, you have the steppers in series (ie, one after the other) where he was talking about parallel driving steppers (2 steppers, instead of an idler pressing the filament against 1 stepper, have 2 whole steppers)... I can't imagine what gains you would get from your style of system? What drove you to do that? Does it work well in practice?

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Could you have a little buffer spoil before the smaller hot end stepper?

Use the large Nema to get filament through long bowden where it then is real loosely coiled, maybe once or twice around a small spool, this way the smaller motor doesn't need to be so closely Synced to larger motor.

One thing you don't want to do is bend the filament by 'wrapping' it around a small spool! It would have to be a large spool which would defeat the purpose of the bowden in the first place which is to keep the mass low.

I really think it would just need to be an existing bowden setup, but modified from:

Bowden > Hotend

To:

Bowden > Micro extruder > Hotend

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