Small steppermotor for Direct Extruder

[isphording90 0]

Hi everyone,

I would like to build a direct extruder. I know that it would be good if things don't get too heavy. So my question is: Can I use other, smaller, stepper motors than the ones that are included with the ultimaker to save weight? And if yes, does anyone know which motors can be used?

 

[jonnybischof 60]

Your motor needs too be up to the task:

It needs enough torque to operate your extruder. I don't know how much that will be, but my guess is it can be much smaller than the big guys used in the UM axes...

Then, it must be compatible to your stepper drivers which means, it must have the same principle of operation (sorry this may be a strange formulation - I'm no native english speaker...).

There are several different types of stepper motors, like 2-phase or 5-phase. And motors may differ in step sizes.

Basically, if you want to drive your smaller stepper motor with the UM electronics, you need one that is the same as the stock UM motors but just smaller. In that case you can just use it without making any changes to the firmware.

You'll probably have to lower the driver current but afaik that's no problem. (My UM is still shipping...)

Then of course, with your new setup, you'll have a different extrusion speed because your setup will probably have a different gear transmission ratio. You'll need to recalculate that when setting up the new extruder. This shouldn't be much of a problem though, maybe contact Daid if there's a simple way to tweak that in Cura?

I'd have a look at these:

http://de.nanotec.com/produkte/250-st4118-schrittmotor-nema-17/

(These are industrial grade so they're not the cheapest, but they should do a good job)

I read somewhere the UM uses NEMA17 (or similar) motors. So they probably have a smaller size version of the same type which should work fine.

 

[isphording90 0]

Thanks for the tips.

If I have understood everything correctly: Can I use this motor?

http://www.stepperonline.com/9deg-nema-17-bipolar-stepper-12a-11ncm156ozin-17hm081204s-p-99.html

 

[isphording90 0]

Where can I find the specifications for the motors used in the ultimaker? I can't find the datasheet or a description in the wiki... :/

 

[Daid 306]

The one in the UM, with the 1:6 gear ratio is overpowered. You could go with less, if you keep the gear ratio. You'll have to experiment to know for sure.

 

[isphording90 0]

Thanks Daid, I will try.

So I need a stepper motor with these specifications:

2-2 Phase

Bipolar - Unipolar?

Each phase draws current 1A / 1.2A at 3.5V / 3.6V

Steps / Step-Angle is important for accuracy (I believe the stock ultimaker motors have 200 steps?)

Is that correct, or is there more?

 

[jonnybischof 60]

At least the current draw is similar - so you probably won't need to make any changes to the stepper driver.

I don't know about the step size, maybe there's something at the RepRap wiki...

2-Phase, bipolar is correct. That makes 4 wires. Unipolar should be 6 wires and is less effective, less popular (I believe I have never seen an unipolar stepper motor before...).

Don't know about the driver's voltage, but as they're current controlled, that shouldn't be an issue. They just need to be able to supply 3.6V at 1.1 A. The larger motors should have the same or higher specs (given they're bigger and stronger) so that should be fine.

It's not necessarily a problem if your motor has a different step size than the original one - that just adds another factor to your motor speed equation. And of course yes, the more steps, the more accuracy. And less maximum possible speed (not an issue on the extruder...).

About the software stuff:

What I wrote before was assuming that the calculations for the motor driver are made in Cura (or whatever other PC software you use) and not inside the Marlin Firmware. That's probably wrong because these programs aren't machine specific so they can't know what the actual equation for the motor speed is.

So probably the PC software just gives a command like "go at 50mm/s" and the Marlin FW does all the calculations. Then you will have to change the firmware OR do the calculations yourself and enter the result in your PC software.

- But those are still only assumptions, I don't know the UM firmware...

 

[illuminarti 18]

...

So probably the PC software just gives a command like "go at 50mm/s" and the Marlin FW does all the calculations. Then you will have to change the firmware OR do the calculations yourself and enter the result in your PC software.

- But those are still only assumptions, I don't know the UM firmware...

 

The gcode specifies the amount of filament to be fed into the printer for each printing head move. Based on the speed and distance for the move, the firmware determines the rate per second at which the filament has to be fed in, and the steps-per-e setting determines the rate at which the firmware has to fire the stepper to achieve it. So, no firmware change should be necessary, if the motor is connected in the same way as the original, to the same pins etc.

The steps-per-e can be set in Cura, so that it gets specified in each print via a gcode command in the header, or it can be stored in EEPROM using the Ulticontroller, or other gcodes.

Note that the number of steps per e - which is a function of the steps-per-revolution of the motor, the microstepping setting, and the gearing for the extruder - does affect performance in a couple of ways. Firstly, for retraction, speed is currently limited by Marlin's limit of 40,000 steps per second (which limits the standard extruder to a speed of about 48mm/s - which is probably more than anyone needs with that design, but in an ideal situation, higher speeds might be beneficial). Lower steps-per-e would help with this.

On the other end, especially with 3mm filament, slow/fine printing requires very small rates of infeed. For this, a very high number of steps-per-e is beneficial, since it allows finer grained control over the amount of filament being fed in. So it's a balancing act between the two use cases. However, with a Bowden-less set up, retraction may be less demanding.

 

[jonnybischof 60]

Well there's still gonna be a bowden tube, isn't it?

Just the extruder will pull the filament out of the boweden tube instead of pushing it into it..

You may also have the same issues with the filament getting stuck in the tube, but at least it'll hardly pop out with your setup

[illuminarti 18]

There will still be a tube of some sort, I presume, but since it's not between the drive and the head, there's a lot less plastic under tension, less variability in the energy in the system, and probably you can get away with shorter retraction distances, as you don't need to worry about taking slack out of the filament in the tube.

 

[jhertzberg 19]

illuminarti, what does a tube do for you in this case?

It seems that the primary problem with a head mounted extruder is the aggregate weight of the motor and the gearing, and of the two, the motor weight is the more difficult to reduce. I wonder about the possibility of using either a flexible drive shaft or a sliding square rod to connect a rear mounted stepper to extruder gearing on the head.

 

[illuminarti 18]

Well, you need some way to get the wiring and the filament to the extruder head without it getting in the way... the current arrangement doesn't seem like too bad of a way to do that.

 

[jhertzberg 19]

I meant the bowden tube specifically. I wouldn't want a bowden adding any friction to retraction if the drive motor was downsized severely, so something with at least a 4mm ID would be a minimum. For the electronics, a lightweight sleeve or coil that stays out of the way seems sufficient. If the extruder gearing is on the head, it may make filament swaps easier to separate the electronics from the filament, or just feed the filament naked to the head.

What do you think of using a flexi-shaft to transmit mechanical energy from a motor mounted on the frame to the head? Do you think that given the torque and low speed that there would be much hysteresis or backlash? There was a RepRap forum thread on this, but it petered out inconclusively, and someone posted a rough design in Feb 2011 as http://www.thingiverse.com/thing:6653

Under the "so crazy it just might work" category, I wish I had the parts to try a sliding square shaft like here http://garyhodgson.com/reprap/2012/01/experimental-off-carriage-extruder-motor/ but with the extruder motor mounted behind a pivot at the right rear corner, the shaft cantilevered in front of the pivot, and the sliding shaft coupler on the head similarly able to pivot. The coupler could potentially bind, but the arc is less than 90 degrees, so perhaps not.

[chopmeister 0]

The flexshaft won't work so don't bother trying. I'm developing a small direct drive extruder for around a year now and I've tried many power transmission types. Sometime last year I tried out a flexshaft based extruder. Everything worked, except the flexshaft itself. The hysteresis causes very very bad walls because of the constant fluctuation of extrusion.

Bear in mind while doing all this that a single NEMA17 motor is much heavier than the whole UM printhead. And that's without a hobbed bolt and all other parts. So if you don't have an effective way of keeping the weight down, you are basically sacrificing all that makes UM faster and more precise than other printers. You get a bit less oozing and retraction problems, but you lose speed and precision.

 

[nick-foley 5]

Agreed. The only real reason I see to make a direct extruder would be printing in highly compressible filaments like TPE, which I haven't tried, but seem like they would bunch up in the bowden tube and have a very long lag time between desired extrusion rate changes.

Nylon does this to some extent because the filament is very soft. The lower speed of a heavy print head wouldn't be a huge problem because I'm getting my best results printing nylon at 30-40mm/s anyway...

 

[jhertzberg 19]

Thanks, chopmeister, for confirming my worry regarding flexshafts. My reason for exploring direct extruders is to come up with a more elegant design for paste extrusion than all of those designs where filament is used to push a syringe plunger or whatnot.

Another design that I have been mulling would be to:

 

1. mount the extruder motor at the top-right-rear above the case,
   
2. which drives a splined shaft running right-rear to right-front,
   
3. which drives bevel gears mounted on the right y sliding block
   
4. which drives a second splined shaft mounted onto and above the y sliding blocks, crossing above the head,
   
5. which drives an extruder assembly mounted on the head.
   

I figure that that even when well lubricated, this assembly adds enough carriage weight and friction that I wouldn't want to even try this without first switching to snowygrouch's direct drive mod. An alternative to splined shafts would be square rods with captured square linear bearings, except that square linear bearings are so expensive in comparison to splined shafts.

 

[nick-foley 5]

Well, if that's your goal, why not just use compressionless housing from a bicycle and make a "reverse bowden" - that acts in compression instead of tension, with a metal or aramid wire rope running down the center - which is compressing a plunger when pulled - and is getting wound up onto a spool by a stepper motor on the back of the Ultimaker.

Or, if you're trying to get away from the plunger entirely, you could probably use two compressionless tubes and power your paste-pushing mechanism by wire drive with the stepper still on the back of the machine.

 

[jhertzberg 19]

Yes, I'm trying to get away from the plunger entirely. I don't want to drag around 60cc of material that may be as heavy as precious metal clay, and I want a more continuous printing process than syringes would allow.

I do like the idea of using two bike bowden cable housings to constrain wire drive cables! I plan on feeding the paste to the head through tubing under pressure, but I want to finely control the feed rate with a small moineau pump on the head, and a wire drive would turn the rotor rather nicely. That's so much easier to provision, build and maintain than the Rube Goldberg contraption that I was coming up with. Thank you!

I apologise for hijacking isphoarding90's thread, but it seems that your solution may serve him as well. Only one question: How would one best cleanly splice the wire (or synchromesh cable) into a closed loop after feeding it through the compressionless tubes?

 

[nick-foley 5]

Hmm, yeah, that's an interesting problem. I'm sure it has been solved by some industry... but my first thought would be to use a braided aramid, like this 2mm spectra: http://www.backpackinglight.com/cgi-bin/backpackinglight/aircore_1_spectra_cord.html#.UfsW55K1Gzk

and then splice it together with some old school rope technique. They actually describe doing this on the product page. Could work well.

 

[ayahoo 0]

Hi guys, nice work you've done here, please have a look at my idea here: (regarding direct extruder)

http://umforum.ultimaker.com/index.php?/topic/3199-crazy-idea-about-feeder/

thanks

 

[yewufakou3 0]

On 7/26/2013 at 5:37 AM, isphording90 said:

Thanks for the tips.

If I have understood everything correctly: Can I use this motor?

http://www.stepperonline.com/9deg-nema-17-bipolar-stepper-12a-11ncm156ozin-17hm081204s-p-99.html

 

 Hi there, can i use this one instead?

https://www.oyostepper.com/goods-64-Nema-17-Stepper-Motor-Bipolar-09-deg-46Ncm-651ozin-2A-28V-42x42x48mm-4-Wires.html

[gr5 2,176]

9 years later!  wow.  That stepper looks good to me but I don't know a lot about steppers.  The most concerning thing is that it mentions 2.8V.  2.8V??  UM puts out 24V to the steppers.  But I think it's the right kind of stepper.  I believe "hybrid" is correct.  And the amperage looks correct.  Everything looks right except that 2.8V.

[gr5 2,176]

I saw another one that was 12V.  Maybe 2.8V *is* a problem?  I don't understand how they can have 2 steppers with the same torque but one says 2.8V and the other says 12V and they both take about 2 amps.  It doesn't make sense to me.

 

Perhaps these are maximum DC voltages that the steppers can handle.  But stepper drivers don't do that they put out sine waves of voltage and current and power.

 

I suspect that stepper will work fine but I'm not a stepper expert.

[gr5 2,176]

Okay I just read this:

Quote

All recent stepper controllers use a current-limiting design. Because of this, the resistance (ohms, Ω) of the coils doesn't matter, as long as it is low enough for the current to rise fast enough for the current-limiting design to come into play. If the resistance is too high (i.e. 24 V steppers) the current simply doesn't raise enough. For this reason, stepper motors rated for 3-5 V and 1-1.5 A are generally recommended, as these motors will perform near their peak torque with a current-limiting stepper controller (such as a Pololu A4988).

 

So I think the stepper is fine.  UM stepper drivers can put out 2Amps but I think they can overheat if they put out more than around 1.2 to 1.5 amps for very long.  The UM2 has software controllable current limiting (which limits the power of the stepper).  If the drivers overheat they shut off for a moment (usually less than a second but the stepper loses position).

 

Only putting out 1 amp is fine as long as you don't try to get too much torque out of the stepper.  If the torque gets too high and the current is limited then you lose a step (the motor "slips").

 

No physical damage is done - it's absolutely fine to do this - but you get underextrusion.  Also you can hear the "click" when the stepper jumps back.